Vector control practices and strategies against West Nile virus.
Date: 2020-11-28
Institutions: European Centre for Disease Prevention and Control, European Food Safety Authority
Subjects: disease prevention, health control, infectious disease, public health

TECHNICAL REPORT

Vector control practices 
and strategies against
 West Nile virus

www.ecdc.europa.eu

ECDC TECHNICAL REPORT 

Vector control practices and strategies 
against West Nile virus 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
      
 
 
 
This report was commissioned by the European Centre for Disease Prevention and Control (ECDC) Specific contract 
No 1 ECD.9918 implementing the joint ECDC and European Food Safety Authority (EFSA) inter-agency framework 
contract for services No ECDC/2019/020, coordinated by Olivier Briët. 

Authors 

Alexandra Chaskopoulou, European Biological Control Laboratory, USDA-ARS, Greece; Marieta Braks, National 
Institute for Public Health and the Environment, the Netherlands; Wim Van Bortel, Institute of Tropical Medicine 
Antwerp, Belgium. 

Acknowledgements 

We would like to thank ECDC National Focal Points for Emerging and vector-borne diseases for their participation in 
the survey. 

We would also like to thank the following: Celine Gossner, Agoritsa Baka, Ines Reulet, Tamas Bakonyi, ECDC; 
Vincent Delvaux, Georgios Gkinis, and Ludovic Chatelin, DG SANTE E4; Willy Wint, Environmental Research Group 
Oxford; Luz Maria Robles, Sacramento-Yolo Mosquito & Vector Control District; Michael Miaoulis, European 
Biological Control Laboratory-USDA-ARS. 

This report was thoroughly reviewed by Paula Macedo, Contra Costa Mosquito & Vector Control District, Roxanne 
Connelly, Centres for Disease Control and Prevention and Francis Schaffner, Francis Schaffner Consultancy. 

Suggested citation: European Centre for Disease Prevention and Control. Vector control practices and strategies 
against West Nile virus. Stockholm: ECDC; 2020. 

Stockholm, November 2020 

ISBN 978-92-9498-523-1 
doi: 10.2900/827636 
Catalogue number TQ-02-20-917-EN-N  

© European Centre for Disease Prevention and Control, 2020 

Cover picture © Guy Hendrickx/ECDC 

Reproduction is authorised, provided the source is acknowledged 

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TECHNICAL REPORT 

Vector control practice and strategies against West Nile virus 

Contents 

Abbreviations ............................................................................................................................................... iv
Glossary ....................................................................................................................................................... iv
Executive summary ........................................................................................................................................ 1
1. Background ............................................................................................................................................... 2
2. Methods .................................................................................................................................................... 3
Survey ..................................................................................................................................................... 3
Literature review ...................................................................................................................................... 3
3. Results ...................................................................................................................................................... 5
The survey ............................................................................................................................................... 5
Section 1. EU/EEA countries....................................................................................................................... 7
Section 2. EU Enlargement and ENP partner countries................................................................................ 13
Literature review .................................................................................................................................... 17
Review of the case studies....................................................................................................................... 19
4. Discussion ............................................................................................................................................... 31
West Nile virus vector surveillance and management capacities in Europe .................................................... 31
West Nile virus vector management - what is the evidence of effect on epidemiological parameters? ............. 33
Limitations of the methodology ................................................................................................................ 34
5. Conclusions and recommendations ............................................................................................................ 35
References .................................................................................................................................................. 36
Annex 1. Questionnaire for the survey ........................................................................................................... 38 

Figures 

Figure 1. Methodological process for presenting information retrieved from the literature review........................... 3 
Figure 2. WNV risk level for EU/EEA, EP, ENP countries, 2019 ............................................................................ 5 
Figure 3. WNV surveillance implementation and funding sources ........................................................................ 7 
Figure 4. WNV surveillance methods among EU/EEA countries ........................................................................... 7 
Figure 5. WNV vector control implementation and funding sources among EU/EEA countries ................................ 8 
Figure 6. Vector control capacities among EU/EEA ............................................................................................ 8 
Figure 7. Constraints and limitations relating to implementation of adulticiding methods among EU/EEA countries .......... 9 
Figure 8. Constraints and limitations relating to implementation of larviciding (biological, chemical), source 
reduction and community outreach campaigns among EU/EEA countries .......................................................... 10 
Figure 9. WNV surveillance implementation and funding sources among EP/ENP countries ................................. 13 
Figure 10. WNV surveillance methods among EP/ENP countries ....................................................................... 13 
Figure 11. Vector control implementation and funding sources among EP/ENP countries .................................... 14 
Figure 12. Vector control capacities among EP/ENP countries ........................................................................... 14 
Figure 13. Constraints and limitations relating to the implementation of adulticiding methods ............................. 15 
Figure 14. Constraints and limitations relating to implementation of larviciding (biological, chemical), source 
reduction and community outreach campaigns ............................................................................................... 16 
Figure 15. Maps depicting number of WNV vector surveillance and control methods applied per country .............. 32 

Tables 

Table 1. Summary of questions asked in the survey .......................................................................................... 4
Table 2. Participating countries in the survey per group ..................................................................................... 6
Table 3. Percentage of EU/EEA countries implementing specific vector control in response to four different triggers ........... 9
Table 4. Percentage of countries implementing specific control in response to four different triggers ................... 14
Table 5. Overview of the case studies included in the analysis of this report ...................................................... 18 
Table 6. Detailed information on WNV vector management experience presented by case study ......................... 29 

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Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

Abbreviations 

Bti 

Bacillus thuringiensis israelensis 

US CDC  United States Centers for Disease Control and Prevention 

ECDC 

European Centre for Disease Prevention and Control 

EU/EEA  European Union/European Economic Area 

ENP 

European Neighbourhood Policy 

IRR 

Incidence rate ratios 

IVM 

Integrated vector management 

LV 

Low volume 

MLE 

Maximum Likelihood Estimates 

ULV 

Ultra-low volume 

WNV  West Nile virus 

Glossary 

Biological larviciding = control of mosquito larvae by introducing natural enemies/predators and/or microbial agents 
applied in the air and on the ground. 

Chemical larviciding = control of mosquito larvae using chemical larvicides applied in the air and on the ground. 

ULV adulticiding = ultra-low volume (ULV) application involves applying low rates of insecticides (with active 
ingredients that degrade rapidly in the environment) in the form of a fine aerosol spray, using an efficient droplet 
size range to target the flying adult vector in outdoor settings. This method is applied in the air and on the ground. 

LV surface spray adulticiding = low volume spraying of insecticides (with long residual effect), applied directly onto 
surfaces/refugia where adult mosquitoes rest. This method is applied on the ground. 

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TECHNICAL REPORT 

Vector control practice and strategies against West Nile virus 

Executive summary 

West Nile virus (WNV) is a vector-borne virus maintained and amplified in nature in an enzootic cycle between 
birds and mosquitoes which, under certain conditions, can spill over to humans and equines. To mitigate the risk of 
WNV being transmitted to humans and animals, European countries have been investing significant resources in 
vector surveillance and control interventions, but with little common knowledge on their effectiveness and no EU-
wide strategy or technical guidance to properly apply these methods and evaluate their efficacy. To help address 
these gaps, ECDC has conducted a survey to collect information on the current WNV surveillance and control 
capacities across European Union/European Economic Area (EU/EEA) countries, European Neighbourhood Policy 
(ENP) partner countries1 and EU candidate/potential candidate countries2 to identify the major challenges faced by 
public health authorities when implementing WNV control strategies. In addition, ECDC has also carried out a 
scoping literature review to collate existing knowledge and operational experience on the effectiveness of vector 
control practices in reducing WNV risk. 

Eighty-three percent of the EU/EEA countries, ENP partner countries and EU candidate/potential candidate 
countries have implemented at least one method of WNV surveillance. The most common passive WNV surveillance 
method for all countries is the detection of human cases, followed by surveillance of dead animals. The most 
common method of active WNV surveillance is mosquito screening, followed by sentinel bird screening and sentinel 
equid screening for EU/EEA countries, ENP partner countries and EU candidate/potential candidate countries. The 
majority of the countries conduct routine vector surveillance (abundance monitoring). However, less than 15% of 
the EU/EEA countries, ENP partner countries and EU candidate/potential candidate countries perform pesticide 
resistance testing, and even in those countries that do, this is not implemented systematically. The majority of the 
EU/EEA countries that do not implement vector control have no history of autochthonous WNV human cases. 
Among countries that implement vector control (58%), the most widely-adopted methods are biological larviciding 
and public education, while the least widely-adopted method is source reduction through environmental 
management. Among ENP partner countries and EU candidate/potential candidate countries, the most widely-used 
methods are public education, followed by biological larviciding, chemical larviciding and low volume (LV) surface 
spray adulticiding. A substantial number of countries include adulticiding in their vector management response 
strategies, including ground-level ultra-low volume (ULV) space spraying, aerial ULV adulticiding and ground-level 
LV surface spraying. EU/EEA countries apply larviciding interventions (in any form) in response to WNV vector 
abundance (larval density) data, however the most important trigger by far for any ULV adulticiding treatment is 
the occurrence of autochthonous WNV human cases. In ENP partner countries and EU candidate/potential 
candidate countries, all available vector control tools (including adulticiding) are routinely implemented in response 
to vector abundance data. 

The scoping literature review targeted published, peer-reviewed manuscripts on controlled studies assessing the 
impact of operational WNV vector control strategies using entomological indicators (adult vector abundance and 
WNV prevalence in mosquitoes), and/or veterinary indicators (enzootic circulation in sentinel/wild animals), and/or 
assessing the impact of vector control directly on human cases. Twelve studies were identified that satisfied the 
above criteria, the majority of which were conducted in the United States. According to the available scientific 
evidence, aerial ULV adulticiding is currently the only method directly linked to (a) reduction in WNV circulation 
levels using entomological/veterinary indicators, (b) interruption of WNV enzootic amplification in a natural-wetland 
environment and (c) interruption of WNV transmission in urban areas resulting in fewer human cases. Source 
reduction (when feasible) and larviciding interventions are justifiably the first and most important step in reducing 
and sustaining vector populations at low levels. There is, however, a critical absence of evidence linking the impact 
of preventive intervention (such as larviciding) to reductions in WNV circulation and transmission levels. 

In general, survey participants identified limited availability of insecticidal active substances, lack of long-term 
registration for products/methods, a complex regulatory framework for the use of biocidal products, and lack of 
EU-wide technical guidelines as significant barriers to effective vector control operations. To address the above 
issues, the first and most important step is to increase communication between all relevant stakeholders. Moreover, 
studies are needed on the impact of vector control measures in order to better inform public health policy decisions 
on strategies for WNV management. 

1 The European Neighbourhood Policy partner countries are: Algeria, Armenia, Azerbaijan, Belarus, Egypt, Georgia, Israel, Jordan, 
Lebanon, Libya, Moldova, Morocco, Palestine*, Syria, Tunisia and Ukraine. 
*This designation shall not be construed as recognition of a State of Palestine and is without prejudice to the individual positions 
of the Member States on this issue. 
2 Under the terms of the EU enlargement policy, the EU candidate countries are Albania, Republic of North Macedonia, 
Montenegro, Serbia and Turkey and the potential candidate countries are Bosnia and Herzegovina and Kosovo† 
†This designation is without prejudice to positions on status and is in line with UNSCR 1244 and the ICJ Opinion on the Kosovo 
Declaration of Independence.  

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Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

1. Background 

West Nile virus (WNV) infection represents a serious burden to human and animal health worldwide because of the 
capacity of the virus to disperse quickly and adapt to a large variety of environments, causing large epidemics. In 
Europe, the virus was detected for the first time in 1958 in Albania and sporadically recorded until 1996, when a 
major outbreak of infection occurred in Romania, characterised by a high fatality rate (10%) with 393 confirmed 
cases [1]. Since then there has been a continuous increase and spread of reported WNV cases in humans and 
horses across Europe. This can partly be attributed to improved surveillance and diagnostic capacities, but also to 
the introduction and establishment of WNV lineage 2 strains which have been responsible for major outbreaks in 
central European and eastern Mediterranean countries, such as Greece, Serbia, Italy, Hungary and Austria [2]. In 
2018, an extraordinary increase in human cases of WNV across the EU/EEA and neighbouring countries was 
observed, with the total number of human infections (n=2 083) far exceeding the total for the previous seven 
years (n=1 832) [3]. Furthermore, the distribution of the virus expanded northwards, with the first equine 
outbreak reported in Germany in 2018, followed by autochthonous human cases in 2019 [3,4]. This unprecedented 
rise in disease incidence, combined with the rapidly growing geographic expansion of the virus indicates the urgent 
need for an increased capacity to address and contain the threat across Europe. 

In 1999, WNV invaded the United States (USA) and within four years spread rapidly across the country, despite 
intensive organised vector control efforts to prevent invasion [5]. A total of 51 747 WNV human cases and 2 381 
deaths (as of January 2020) have been recorded since the introduction of the virus, which is currently considered 
to be the leading cause of mosquito-borne disease in the continental USA [6,7]. Significant research efforts have 
been dedicated to deciphering the complex ecology of the virus in order to better predict and contain outbreaks, 
while significant improvements have been made to vector surveillance and control programmes across the country. 
However, the primary factors preventing the reduction of WNV in the USA have been identified as the uneven 
distribution of adequate surveillance and control capacities (leaving gaps in preparedness and response) [8], 
inconsistent vector surveillance activities and delays in acting upon surveillance indicators [9]. 

There is a plethora of laboratory-based and small-scale field studies demonstrating the impact of vector control 
methods on the abundance of WNV vectors. However, controlled, large-scale, operational studies assessing the 
impact of control methods on vector abundance, while making the link between entomological efficacy and 
epidemiological impact, are scarce. Moreover, the vast majority of these studies have been conducted in the USA 
[10]. Such studies are very demanding in terms of resource requirements (technologies, tools, expertise), 
committed funding and interdisciplinary collaboration (entomologists, epidemiologists, regulators, physicians and 
vector control professionals in academia, state institutions, industry and the private sector). The knowledge and 
experience accumulated in the USA from these few studies is valuable. Nevertheless, it is important to understand 
the operational context of vector control studies in order to properly relate, compare and interpret them within a 
European context. The operational context takes into account the environmental, financial, regulatory and societal 
parameters defining a specific region. The impact of any vector control tool applied at an operational level, even 
when it is applied by the most experienced professionals with the best available technologies, is always limited by 
the following factors: 

 

 
 

environmental (i.e. a treatment can only be effective if it reaches the target at the effective dose and physical, 
or other obstructions commonly prevent homogeneous treatments); 
financial (i.e. treatment cost and budget availability directly affects the scale and frequency of interventions); 
regulatory (i.e. legislation can restrict access to larval habitats, or limit frequency of treatments), and societal 
(i.e. societal acceptability of methodologies). 

European national (country-based) and local (region/municipality-based) public health agencies are important 
actors in the defence against mosquito-borne disease. National and regional WNV surveillance and response plans 
are in place in some countries [11-13], with a variety of WNV risk mitigation strategies and vector control 
interventions. 

This report aims to identify and evaluate the operational challenges each country is facing in implementing vector 
control and to prioritise the needs to be addressed in order to facilitate national public health authorities in 
developing and/or enhancing their national WNV response capacities. In addition, existing knowledge and 
operational experience on the effectiveness of vector control practices in reducing WNV risk was collated through a 
scoping literature review. This review aimed to identify, present and discuss studies on applied aspects of vector 
control under specific operational scenarios of WNV management, to establish what worked, where and why, and 
equally, to ascertain what did not work and why. 

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TECHNICAL REPORT 

Vector control practice and strategies against West Nile virus 

2. Methods 

Survey 

The survey was administered online via the EU Survey tool and targeted all EU/EEA countries (n=31), EU candidate 
and potential candidate countries (n=7) and ENP partner countries (n=16). The survey was distributed via the local 
focal points of ECDC’s Emerging and Vector-borne Diseases (EVD) network and representatives from the ENP 
partner countries and EU candidate and potential candidate countries. The focal points were responsible for 
reaching out to national vector control authorities and assembling the information requested by the survey. Where 
applicable, sub-national/regional representatives also completed the survey. The survey consisted of 13 questions 
(Table 1) addressing four main topics:  

  WNV surveillance capacities (vector abundance, WNV surveillance through mosquito and sentinel animal 

screening, dead animal surveillance, human case detection, pesticide resistance testing);  

  WNV vector control capacities;  
 
challenges and constraints relating to vector control implementation. 

criteria for implementing WNV vector control; 

The last question (number 13) was a general open question, allowing respondents to elaborate on their general 
experience in relation to WNV vector management in their countries or regions. For the complete questionnaire, 
see Annex 1. 

Table 1. Summary of questions asked in the survey 

WNV status 

1 

What is the current WNV risk level applied to your country/region? 

Surveillance 
2 

Is WNV surveillance conducted at national, regional or local level? 

3 

4 

5 

Who conducts surveillance in your country? 

Who funds WNV surveillance in your country? 

Which WNV surveillance activities are performed in your country? 

Vector control 
6 

Who conducts vector control in your country? 

7 

8 

9 

10 

Guidelines 
11 

Who funds vector control in your country? 

What specific control measures are implemented, depending on different risk levels? 

What are the most important constraints for implementing each vector control measure? 

Vector control methods: evaluation 

Do you need technical guidelines for WNV mosquito vector surveillance? 

12 

Do you need technical guidelines for WNV mosquito vector control? 

Open question 
13 

Additional information issues/challenges. 

Literature review 

The scoping review focused on peer-reviewed, controlled studies published within the last two decades. The 
following inclusion criteria were used: (a) studies assessing the impact of operational WNV vector control strategies 
using entomological indicators (adult vector abundance in parallel to WNV prevalence in mosquitoes); (b) studies 
assessing the impact of operational WNV vector control strategies on enzootic circulation of WNV (sentinel/wild 
animals); (c) studies assessing the impact of operational WNV vector control strategies on human cases. Only 
studies applied under field conditions  defined as any community or environment where WNV vectors naturally 
occur with ongoing WNV transmission  were included. Due to the limited studies available in Europe 
demonstrating the impact of vector control on WNV circulation levels, an additional search was conducted for 
studies with efficacy estimates solely based on entomological outcomes in the European region, demonstrating the 
impact of larviciding/adulticiding methods against adult Culex populations under operational settings. Non-
operational studies, or studies assessing the impact of control methods based solely on larval density (without 
making a link to the impact on adult vector populations) were excluded. The most recent effort to review WNV 
vector control measures in Europe was published in 2014 [14], covering studies published until 2011 and our 
efforts therefore focused on the post-2011 period. 

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Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

A literature review was performed by searching bibliographic databases (PubMed), Internet sources (Google 
Advanced search) and the websites of relevant public health and vector control authorities  i.e. US CDC, ECDC, 
the European Mosquito Control Association (EMCA), the American Mosquito Control Association (AMCA), ministries 
of health/local departments of public health, mosquito and vector control districts  to identify studies evaluating 
WNV vector control practices. Studies (including review articles) found were also used to identify other relevant 
studies and websites. The searches were limited to the English language and combined the concepts within the 
scope of this project: WNV vector management strategies, specific control methods/tools (e.g. larviciding, 
adulticiding) and their impact on WNV circulation levels. Search terms were in three main groups: disease-relevant 
terms, vector-relevant terms and intervention-relevant terms. For the disease group, the terms were ‘West Nile 
virus’, ‘West Nile fever’ and ‘WNV’. For the vector group the terms were ‘Culex’ and ‘Culex pipiens’. For the 
intervention category the terms were ‘integrated vector management’, ‘larviciding’, ‘adulticiding’ and ‘source 
reduction’. To increase the focus on Europe, the above terms were combined (through the AND operator) with 
specific European countries having a long history of WNV outbreaks: Italy, Greece, France and Serbia.  

The manuscripts that satisfied the inclusion criteria were further categorised into ‘case studies’ based on the 
geographic location of the interventions (more than one manuscript fitting the criteria could apply to one case 
study) (Figure 1). For each case study, an additional literature search was conducted to retrieve information on the 
history of WNV transmission, ecological parameters related to WNV transmission (environment, climate, vectors) 
and vector control capacities (resources, budget) associated with the specific geographical region. All relevant 
information was presented in the following format: study site, land area and population, climate (e.g. temperate, 
arid), environment (e.g. urban, agricultural), vector species targeted (e.g. Culex pipiens), budget of organised 
vector control programmes (where applicable), vector control methods applied (e.g. larviciding, adulticiding), WNV 
surveillance methods applied, timing of interventions (before or after human cases, or both), 
assessment/evaluation of efficacy (mosquito infection rates, and/or sentinel animal seroconversions, and/or impact 
on human cases, all of the above) and main conclusions. Where necessary, WNV management experts involved in 
the selected case studies were approached to provide additional information or clarifications relating to their 
research. 

Figure 1. Methodological process for presenting information retrieved from the literature review 

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Vector control practice and strategies against West Nile virus 

3. Results 

The survey 

Participating countries 

In total, 47 responses were received (39 from national authorities, eight from regional authorities) from 25 EU/EEA 
countries, six ENP partner countries and six EU candidate/potential candidate countries (Table 2). Two of the 
participating countries submitted two questionnaires each at national level, however only one questionnaire per 
country was included in the analysis. One questionnaire form was only partially completed (responses provided for 
Questions 1, 11, 12) and therefore excluded from the analysis of the remaining questions. Data were analysed 
separately in two groups – one for EU/EEA countries and one for ENP partner and EU candidate/potential candidate 
countries, and the results are reported in two sections accordingly. For all questions, results are presented at 
country level (except for Questions 8 and 9 where responses from the eight regional authorities were included in 
the analysis). 

Table 2. Participating countries in the survey per group 

European Union/EEA 

EU Neighbourhood Policy 

EU Enlargement Policy 

Albania 
Bosnia Herzegovina 
Kosovo 
Montenegro 
Republic of North 
Macedonia 
Serbia 
Turkey 

√ 
√ 
√ 
√ 

√ 

√ 

Algeria 
Armenia 
Azerbaijan 
Belarus 

Egypt 

Georgia 
Israel 
Jordan 
Lebanon 
Libya 
Moldova 
Morocco 
Palestine  
Syria 
Tunisia 
Ukraine 

√ 

√ 

√ 

√ 

√ 

√ 

Austria 
Belgium 
Bulgaria 
Croatia 

Republic of Cyprus 
Czech Republic 
Denmark 
Estonia 
Finland 
France 
Germany 
Greece 
Hungary 
Ireland 
Italy 
Latvia 
Lithuania 
Luxembourg 
Malta 
Netherlands 
Poland 
Portugal 
Romania 
Slovakia 
Slovenia 
Spain 
Sweden 
Iceland (EEA) 
Liechtenstein (EEA) 
Norway (EEA) 
United Kingdom 
(former EU member) 

√ = responded 

√ 
√ 
√ 
√ 

√ 

√ 

√ 
√ 
√ 
√ 
√ 
√ 
√ 
√ 
√ 
√ 
√ 
√ 

√ 
√ 
√ 

√ 

√ 
√ 

√ 

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TECHNICAL REPORT 

WNV risk level of participating countries (Question 1) 

According to the responses received from 25 EU/EEA countries, 40% reported at least one WNV human case 
(according to EU case definition) in 2019 (risk level 5 according to ECDC’s WNV risk assessment tool, Figure 2). In 
12% of the countries there is past evidence of WNV circulation (risk level 2), while in 48%, risk level 1 is applicable 
(ecological conditions suitable but no historical transmission). 

Four EU candidate/potential candidate countries declared that they had WNV circulation during 2019. Two of those 
countries declared detection of at least one human case (risk level 5), one declared WNV detection in horses (risk 
level 4) and one declared evidence of WNV circulation in mosquitoes or birds (risk level 3). Among the participating 
ENP partner countries, one reported at least one human case during 2019 (risk level 5). Four countries declared 
past evidence of WNV circulation (risk level 2) and one declared risk level 1 as being applicable (ecological 
conditions suitable but no historical circulation). 

Figure 2. WNV risk level for EU/EEA, EP, ENP partner countries, 2019* 

*The risk levels are defined in accordance with ECDC’s WNV risk assessment tool available at: 
https://www.ecdc.europa.eu/sites/default/files/media/en/publications/Publications/west-nile-virus-risk-assessment-tool.pdf 

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Vector control practice and strategies against West Nile virus 

Section 1. EU/EEA countries 

WNV surveillance implementation and funding (Questions 2, 3 and 4) 

WNV surveillance is implemented by the state, academia, and private sector. In 54% of responses, the state is 
involved in surveillance implementation, followed by academia and the private sector (25% and 17%, respectively). 
In most countries, surveillance activities are funded by national and/or regional sources (54% and 33%, 
respectively). In 25% of the countries, academia is involved in funding surveillance (Figure 3). 

Figure 3. WNV surveillance implementation and funding sources (N=24) 

WNV surveillance capacities (Question 5 & 11) 

Most countries (83%) implement at least one method of active or passive WNV surveillance (Figure 4). The most 
common passive WNV surveillance method is the detection of human cases (75%), followed by surveillance of 
dead animals (55%). The most common method of active WNV surveillance is mosquito screening, followed by 
sentinel bird screening and sentinel equid screening. The percentage of countries that implement routine mosquito 
surveillance (mosquito abundance monitoring) is 65%. Human WNV infection surveillance is performed in 75% of 
the EU/EEA countries. Only 15% of the countries perform pesticide resistance testing. Sixty-eight percent of the 
countries indicated that there is a need for technical guidelines on WNV surveillance. 

Figure 4. WNV surveillance methods among EU/EEA countries (N=24) 

Left panel: Percentage of countries that implement at least one surveillance method.  
Right panel: Percentage of adoption  surveillance methods among countries implementing surveillance. 

WNV vector control implementation and funding (Questions 6 & 7) 

In the EU/EEA, 58% of countries implement at least one vector control method. Vector control activities are funded 
and implemented by a combination of state (national, regional) and private institutions (Figure 5). In 21% of the 
countries vector control is conducted and funded exclusively by the state, whereas in 8% of the countries vector 
control is conducted exclusively by the private sector. 

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Figure 5. WNV vector control implementation and funding sources among EU/EEA countries (N=24) 

WNV vector control capacities and implementation triggers (Question 8) 

The most common control methods in EU/EEA countries are biological larviciding (86%) and public campaigns 
(79%), followed by ground ULV adulticiding (43%), application of water surface films (43%), aerial ULV 
adulticiding (36%), ground LV surface sprayings (36%), chemical larviciding (36%) and source reduction (36%, 
Figure 6). In total, 84% of respondents agreed that vector control guidelines were needed. 

Figure 6. Vector control capacities among EU/EEA (N=24) 

Left panel: Percentage of countries implementing vector control.  
Right panel: Percentage of adoption  vector control methods. 

For any adulticiding treatment (ground ULV, aerial ULV or ground LV), the most important trigger by far is the 
detection of WNV human cases, followed by the detection of WNV-positive mosquitoes/birds and a high adult 
vector population (Table 3). 

Larviciding by chemical, biological, or mechanical means (water surface films) is applied in response to high vector 
abundance (larval indices) by 71%, 83%, and 83% of the countries/regions (Table 3). All larviciding methods are 
intensified in response to WNV human cases. Larval source reduction is a strategy adopted by 90% of the 
countries/regions in response to high vector abundance (Table 3). Community outreach interventions become 
progressively more intensive as the WNV risk level increases; 60% of the countries/regions routinely perform 
community outreach activities in response to high vector populations and intensify their efforts depending on the 
WNV risk level (100% of the countries/regions perform community outreach in response to WNV human cases). 

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Vector control practice and strategies against West Nile virus 

Table 3. Percentage of EU/EEA countries implementing specific vector control in response to four 
different triggers 

Vector 
control 
target 

Adults 

Immature 
stages 

Vector control 
intervention 

Aerial ULV 
Ground ULV 
Ground LV 
Chemical larviciding 
Biological larviciding 
Water surface films 
Source reduction 
Community outreach 

Trigger for vector control implementation 

High vector 
population 

50% 
33% 
58% 
83% 
71% 
83% 
90% 
60% 

WNV-positive 
mosquitoes or 
birds 
50% 
33% 
58% 
92% 
76% 
83% 
80% 
80% 

WNV-positive 
horses 

WNV human 
cases 

17% 
17% 
50% 
83% 
71% 
75% 
90% 
73% 

100% 
100% 
100% 
92% 
82% 
100% 
100% 
100% 

Constraints and limitations relating to vector control (Question 9) 

Question 9 aimed to identify the specific constraints/challenges (such as regulatory constraints, limited availability 
of products, operational capacity, cost) faced by each country/region in implementing the various WNV vector 
control methods. The respondents were asked to rate the constraints associated with each method from one to five 
(with five being the strongest level of constraint, and one being the weakest). If the participants had no experience 
of the method, they were asked to leave it blank. 

More than 40% of the respondents declared lack of knowledge relating to the constraints or limitations in 
implementing all vector control methods. More than 40% of the respondents agreed that the most important 
challenges for adulticiding are regulatory constraints, limiting either the frequency of the treatments or the size of the 
treated areas (Figure 7). Product availability, followed by high cost are also considered to be important constraints for 
the application of aerial and ground ULV adulticiding in some countries. For chemical and biological larviciding the 
most important constraints are product availability and a limited number of products with long residual activity (Figure 
8). High cost appears to be a more important constraint for biological larviciding than chemical larviciding (on average 
18% of the respondents declared cost to be a concern for biological larviciding compared to 7% for chemical 
larviciding). Operational capacity followed by community acceptance, are the most important limitations to the 
implementation of larval source reduction and communication outreach/education campaigns. 

Figure 7. Constraints and limitations relating to the implementation of adulticiding methods among 
EU/EEA countries 

9 

 
 
 
 
 
Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

Figure 8. Constraints and limitations relating to the implementation of larviciding (biological, 
chemical), source reduction and community outreach campaigns among EU/EEA countries 

10 

 
 
 
 
 
 
TECHNICAL REPORT 

Vector control practice and strategies against West Nile virus 

Additional issues/challenges relating to WNV surveillance and control 
(Question 13)  

In the last survey question, the respondents were asked to provide any additional information on issues or 
challenges that they are facing in WNV vector surveillance and control in their countries/regions. Among the 20 
responses from EU/EEA countries, at least half were clear and detailed enough to provide insight on how certain 
issues affect surveillance and vector control at local level. The most frequently recurring issues are summarised 
below. 

Regulatory constraints 
Regulatory constraints were brought up repeatedly in many of the responses. Issues that were reported include 
limitations on the application parameters for the larvicides currently available, preventing areas from being treated, 
or receiving sufficiently frequent treatment. Large areas of natural wetlands may be excluded from treatment 
because of their protected status. Restrictions on application parameters of biological larviciding with Bacillus 
thuringiensis israelensis (Bti) (applications restricted to every 10 days and no more than eight applications per 
season) prevent the effective implementation of vector control programmes in some countries. 

‘The current regulations for larviciding exempt large productive areas from being treated (NATURA). These 
areas are productive in WNV vectors and in proximity to residential areas. More than 20 000 hectares of 
productive natural wetlands are found in our region.’ 

‘Current regulations for Bti limit the number and frequency of applications. We can only make eight 
applications per area with a 10-day interval. Our needs are much greater than this, especially during the 
months of July and August when re-application is required every five days in some regions.’ 

Restrictions on adulticiding treatments are also mentioned. Respondents reported that the current regulatory 
framework limits aerial ULV adulticiding treatments to 2 km buffer zones from residential areas. Buffer zones also 
apply to ground ULV adulticiding treatment in some countries (100 m from residential areas). The respondents 
were concerned that these restrictions were affecting the efficacy of the treatment and also expressed their doubts 
about the scientific merit of these decisions. 

‘Current regulations for aerial ULV (a very effective method in reducing Cx. pipiens abundance and WNV 
infection rates) limit the applications to 2 km distance from residential areas - thus decreasing the impact 
this method can have near people who are at risk of WNV infection.’ 

‘The current regulations for ground ULV applications are being restricted to 100 m from residential areas. 
We do not understand how these buffer zones are chosen, looks like a completely arbitrary decision.’ 

One respondent commented that the current regulatory framework is inflexible and does not account for 
environments with a high level of complexity and vector abundance, underlining the fact that all available vector 
control methods are needed in order to overcome the challenges in the field. 

‘Dense vegetation and lack of access may prevent areas from being treated effectively with larvicides. ULV 
space sprays are susceptible to weather conditions and are affected by densely populated areas (tall, dense 
buildings) that may obstruct the treatment. It becomes clear that the challenges in the field (practical 
challenges) are such that they require a diverse set of methods and products. Also, realistic regulations are 
needed to facilitate the application of all available methods.’ 

Biocides availability 
Concerns about the restricted number of registered products (larvicides and adulticides) and their limitations in 
efficacy were raised. For a wide range of very productive larval habitats, such as rice-fields and natural wetlands, 
the only registered product is Bti, which is known to be less effective in rich organic environments. Concerns about 
the development of pesticide resistance development, especially to pyrethroids, are also expressed, emphasising 
the need for a wider range of products and active ingredients to cope with this.  

‘The most important challenge for us is the current regulatory framework that limits the number of products 
available for vector control. For example, we have only one product (Bti) available for larviciding.’ 

11 

 
 
 
Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

‘The field context often limits the efficacy of the various control methods. For example Bti is not as effective 
in a heavily organic environment against Cx. pipiens.’ 

‘For our adulticiding treatments we only have one group of chemicals (pyrethroids). With this limited 
number of active ingredients we are concerned about the development of insecticide resistance. We need a 
wide range of products that would allow for rotations to help prevent the development of resistance.’ 

Constraints related to budget and expertise 
The issue of lack of funding was raised in multiple questionnaires. Some countries consider WNV 
surveillance/control not to be a high priority and therefore no investment is made in this area. Comments were also 
provided regarding the lack of expertise in the entomological and vector control sector. 

‘(WNV) is not seen as a public health issue by many health authorities.’ 

‘In our opinion, the main constraints for implementing a complete surveillance system on WNV are the lack 
of funding, alongside the shortage in human resources.’ 

‘Limited local expertise, limited human resources, no local entomologists.’ 

‘Lack of a network of entomologists with responsibilities for vector surveillance and control.’ 

Vector control budgeting issues were also identified by respondents and attributed to the low number of larvicides 
available on the market. In particular, the only product currently registered for use in natural wetlands and rice fields 
is costly and has a short residual effect, requiring recurrent application. This may have a significant effect on the 
sustainability of the larviciding programmes. Concerns were also raised about the creation of a ‘monopoly’ in Europe’s 
biocide market. 

‘This product has a short residual impact (24 hours in liquid form) and re-application is needed, significantly 
raising the cost of our programme.’ 

‘We are also concerned about the creation of a monopoly in the field of public health and we are worried for 
the ramifications this may have for the future of vector control in our country.’ 

Societal constraints 
The unwillingness of the community to cooperate was identified as an important constraint. Difficulties in gaining 
access to private houses and reluctance to follow instructions provided by vector control personnel were reported. 

‘An important source of Cx. pipiens breeding sites are private houses – we spend significant resources to 
access private property and educate citizens, however often no access is granted to our personnel and also 
citizens often do not cooperate, despite receiving information and educational material about reducing 
vector breeding sites. We need to find a way to compel citizens to take action.’ 

‘Even though we perform regularly door-to-door educational campaigns it is often difficult to gain access in 
private property. Also, bad practices in agriculture (e.g. intentional flooding for animal grazing) further 
increases the complexity of vector control.’ 

‘Another challenge is raising public awareness and enthusiasm about domestic source reduction and 
personal protective measures.’ 

12 

 
 
 
 
TECHNICAL REPORT 

Vector control practice and strategies against West Nile virus 

Section 2. EU Enlargement and ENP partner countries 

WNV surveillance implementation and funding (Questions 2, 3 & 4) 

WNV surveillance is implemented by the state, academia and the private sector (Figure 9). In 83% of cases the 
state is involved in surveillance implementation, followed by the private sector (25%) and academia (8%). 
Surveillance activities are funded exclusively by national and/or regional sources (83% and 17%, respectively). 

Figure 9. WNV surveillance implementation and funding sources among ENP partner countries and 
EU candidate/potential candidate countries (N=12) 

Who conducts surveillance

Who funds surveillance

0%

25%

50%

75% 100%

0%

25%

50%

75% 100%

Government

83%

National Gov

83%

Academia

8%

Regional Gov

8%

Private

25%

No response

17%

None

17%

WNV surveillance capacities (Questions 6 & 7) 

Most countries implement at least one method of active or passive surveillance (83%, Figure 10). The most 
common passive WNV surveillance method is the detection of human cases (90%), followed by surveillance of 
dead animals (30%). The most common method of active WNV surveillance is mosquito screening, followed by 
sentinel surveillance of equids (30%) and sentinel surveillance of birds (10%). Eighty percent of the countries 
within this group implement routine mosquito surveillance. Pesticide resistance testing is performed in 10% of the 
countries (Figure 10). All twelve countries in this group indicated a need for technical guidelines on WNV 
surveillance. 

Figure 10. WNV surveillance methods among ENP partner countries and EU candidate/potential 
candidate countries (N=12) 

Left panel: Percentage of countries that implement at least one surveillance method.  
Right panel: Percentage of adoption of surveillance methods among countries implementing surveillance. 

WNV surveillance implementation 
percentage

Percentage of adoption of surveillance methods

17%

83%

0%

25%

50%

75%

100%

Routine mosquito surveillance

80%

Mosquito WNV screening

50%

Sentinel Birds WNV screening

10%

Sentinel equids WNV screening

Passive Surveillance dead
animals

30%

30%

Human cases

90%

EP/ENP Countries that implement WNV Surveillance

Pesticide resistance testing

10%

EP/ENP Countries that don't implement WNV Surveillance

WNV vector control implementation and funding 

Vector control is conducted by the state in 83% of the countries, whereas the private sector is involved in 25% of 
cases. Vector control is funded by national and/or regional sources in 75% and 33% of the countries, respectively. 
In two countries, vector control is funded by academia, and in another two countries it is funded by the private 
sector (Figure 11). 

13 

 
 
 
 
 
 
Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

Figure 11. Vector control implementation and funding sources among ENP partner countries and EU 
candidate/potential candidate countries (N=12) 

Who conducts vector control

Who funds vector control

0%

25%

50%

75% 100%

0%

25%

50%

75% 100%

Government

83%

National Gov

75%

Private

25%

None

17%

Regional Gov

33%

Academia

Private sector

8%

8%

None

17%

WNV vector control capacities and implementation triggers 

Eighty-three percent of the ENP partner countries and EU candidate/potential candidate countries implement at 
least one vector control methodology (Figure 12). The most common vector control method is communication 
campaigns (60%), followed by chemical larviciding (50%), biological larviciding (50%) and ground LV surface 
spraying (50%). Aerial ULV adulticiding, ground ULV adulticiding, application of water surface films and larval 
source reduction are implemented in 40% of the countries. Eleven of the twelve countries confirmed the need for 
vector control guidelines.  

Figure 12. Vector control capacities among ENP partner and EU candidate/potential candidate countries (N=12)  

Left panel: Percentage of countries implementing vector control.  
Right panel: Percentage of adoption  vector control methods. 

Vector control implementation percentage

Percentage of adoption of vector control 
methods 

0%

25% 50% 75% 100%

0%

25% 50% 75% 100%

EP/ENP Countries that
implement vector control

83%

EP/ENP Countries that don't
implement vector control

17%

Ground LV surface sprayings

Ground ULV adulticiding

Aerial ULV adulticiding

Chemical larviciding

Biological larviciding

Water surface films

Source reduction

Community education

50%

40%

40%

50%

50%

40%

40%

60%

Larviciding using chemical or biological means, larval source reduction and communication campaigns are 
performed in response to high vector abundance in all countries (100%, Table 4). Ground LV, aerial ULV and 
ground ULV adulticiding treatments are triggered in response to high vector population in 80%, 75% and 67% of 
the countries, respectively. All vector control interventions appear to be applied routinely on the basis of high 
vector abundance, irrespective of the WNV risk level. 

Table 4. Percentage of countries implementing specific control in response to four different triggers 

Vector 
control 
target 

Adults 

Immature 
stages 

Vector control 
intervention 

Aerial ULV 
Ground ULV 
Ground LV 
Chemical larviciding 
Biological larviciding 
Water surface films 
Source reduction 
Community outreach 

Trigger for vector control implementation 

High vector 
population 

75% 
67% 
80% 
100% 
100% 
75% 
100% 
100% 

WNV-positive 
mosquitoes or 
birds 
25% 
67% 
40% 
50% 
25% 
50% 
50% 
33% 

WNV-positive 
horses 

WNV human 
cases 

25% 
33% 
20% 
25% 
25% 
25% 
25% 
17% 

25% 
67% 
40% 
50% 
25% 
50% 
50% 
33% 

14 

 
 
 
 
 
 
TECHNICAL REPORT 

Vector control practice and strategies against West Nile virus 

Constraints and limitations relating to vector control (question 9) 

More than 60% of the respondents declared a lack of knowledge relating to the constraints or limitations on 
implementing all vector control methods. Twenty-five percent of the respondents agreed that the most important 
challenge for both ground and aerial ULV adulticiding is high cost, limiting either the frequency of the treatment or 
the size of the treated areas (Figure 13). Furthermore, regulatory constraints are considered to be an important 
factor limiting the application of aerial ULV adulticiding in some countries. For chemical and biological larviciding 
the most important limitations are regulatory constraints and high cost, respectively (Figure 14). High cost and 
operational capacity are the most important limitations in the implementation of larval source reduction and 
communication outreach/education campaigns, respectively. 

Figure 13. Constraints and limitations relating to the implementation of adulticiding methods 

Aerial ULV adulticiding 

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

High cost that limits application frequency

High cost that limits coverage

Operational capacity

Product availability

Regulatory constraints that limits application frequency

Regulatory constraints that limits coverage

8 

8 

25 

17 

17 

8 

8 

8 

8 

8 

8 

8 

17 

17 

17 

8 

25 

Community acceptance

8 

17 

8 

8 

67 

58 

58 

83 

67 

50 

58 

*

**

***

****

*****

Don't know

Ground  ULV adulticiding

0%

20%

40%

60%

80%

100%

High cost that limits application frequency

8 

17 

High cost that limits coverage

17 

17 

25 

8 

17 

Operational capacity

8 

17 

17 

8 

Product availability

17 

17 

Regulatory constraints that limits application frequency

25 

Regulatory constraints that limits coverage

Community acceptance

17 

17 

8 

8 

8 

8 

8 

8 

8 

50 

50 

42 

67 

67 

58 

58 

*

**

***

****

*****

Don't know

Ground LV residual adulticiding

0%

20%

40%

60%

80%

100%

High cost that limits application frequency

High cost that limits coverage

Operational capacity

Product availability

No/limited products with long residual efficacy

Regulatory constraints that limits application frequency

Regulatory constraints that limits coverage

8 

8 

8 

8 

17 

17 

17 

25 

25 

Community acceptance

*

**

***

33 

****

8 

8 

17 

8 

8 

17 

17 

17 

8 

8 

8 

8 

67 

67 

67 

67 

58 

58 

58 

58 

*****

Don't know

15 

 
 
 
 
 
 
 
Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

Figure 14. Constraints and limitations relating to the implementation of larviciding (biological and 
chemical), source reduction and community outreach campaigns 

Chemical larviciding

0%

20%

40%

60%

80%

100%

High cost that limits application frequency

High cost that limits coverage

Operational capacity

Product availability

No/limited products with long residual efficacy

Regulatory constraints that limits application frequency

Regulatory constraints that limits coverage

Community acceptance

8 

8 

8 

17 

17 

8 

17 

17 

17 

17 

17 

8 

8 

8 

-

8 

8 

8 

8 

17 

8 

8 

8 

8 

8 

8 

67 

67 

67 

67 

67 

67 

67 

58 

*

**

***

****

*****

Don't know

Biological larviciding

0%

20%

40%

60%

80%

100%

High cost that limits application frequency

High cost that limits coverage

Operational capacity

Product availability

17 

17 

25 

25 

8 

17 

17 

8 

8 

No/limited products with long residual efficacy

17 

8 

Regulatory constraints that limits application frequency

Regulatory constraints that limits coverage

Community acceptance

8 

8 

8 

17 

17 

17 

58 

67 

67 

67 

75 

75 

75 

75 

*

**

***

****

*****

Don't know

16 

 
 
 
 
 
 
 
 
TECHNICAL REPORT 

Vector control practice and strategies against West Nile virus 

Literature review 

Search results 

A total of 389 manuscripts were identified from the databases and websites. After removing manuscripts which 
were outside the scope of WNV vector management (n=332), 57 manuscripts remained for closer analysis. The 
majority of these were laboratory based/semi-field studies, larviciding efficacy studies demonstrating impact solely 
on larval mortality, WNV control review documents and WNV vector surveillance studies. An additional two 
manuscripts were identified from the reference list for these manuscripts. One operational study in the EU was 
identified [15] during the post-2011 period demonstrating the impact of larviciding and adulticiding methods 
against adult Culex populations. The study was primarily designed to target Aedes albopictus and although efficacy 
against adult Cx. pipiens populations was reported, there was no link to or assessment made of the WNV 
transmission risk. In total, twelve manuscripts satisfied all inclusion criteria. These were divided into eight case 
studies, according to their geographical regions. Seven of the regions are in the USA (California, Louisiana, Texas, 
Georgia, Colorado, and Illinois) and one is in Europe (Greece) (Table 5). 

 
 
 
 
 
 
 
 

Case study 1. St. Tammany Parish, LA [16] 
Case study 2. Sacramento-Yolo Counties, CA [17-20] 
Case study 3. Coachella Valley, CA [21] 
Case study 4. Central Macedonia Region, GR [22] 
Case study 5. North Central Texas, TX [23,24] 
Case study 6. City of Chicago, IL [25] 
Case study 7. Atlanta, GA [26] 
Case study 8. Fort Collins, CO [27]. 

In case studies 1-4, WNV vector management interventions were conducted under the umbrella of a centralised, 
organised vector control programme. For case studies 5-8, surveillance and/or control interventions were 
supported by city or municipality-based health departments. Table 5 below summarises the experiences gained 
from these eight separate case studies in relation to WNV management. 

17 

 
 
 
Vector control practice and strategies against West Nile virus  

TECHNICAL REPORT 

Table 5. Overview of the case studies included in the analysis of this report 

Case study 

Land 
area* 
(km2) 

Population* 

Climate 
(Köppen 
classification) 

Environment 

Research 
manuscripts 
identified 

WNV vector 
species targeted 

Treatments were 
conducted under the 
umbrella of a centralised 
state funded vector 
control programme 
(annual budget 
provided)** 
USD 8 100 000 (2017)a 

Vector control 
funding per 
capita/per km2 

USD 31.38/3 702 (2017) 

USD 15 060 623 (2018)b 

USD 8.55/2 940 (2018) 

USD 10 849 764 (2019)c 

USD 27.98/6 279 (2019) 

EUR 2 700 000 (2019)d,e 

EUR 1.73/144 (2019) 

N/A 

N/A 

N/A 

N/A 

1. St. Tammany 
Parish, LA, USA 

2. Sacramento and 
Yolo Counties, CA, 
USA 

3. Coachella Valley, 
CA, USA 

4. Central 
Macedonia Region, 
Greece 

5. North Central 
Texas (Collin, 
Dallas, Denton, 
Tarrant Counties) 
TX, USA 
6. City of Chicago, 
IL, USA 

7. Atlanta (Dekalb 
and Fulton 
Counties), GA, USA 
8. Fort Collins, CO, 
USA 

2 188 

258 111 

5 122 

1 760975 

Humid-sub-
tropical 

Mediterranean 
hot summer 

1 728 

387 737 

Hot semi-arid 

18 811 

1 564 736 

Mediterranean 
hot summer 

8 943 

6 586 913 

Humid-sub-
tropical 

Urban/rural, natural 
wetlands (swamps, 
salt marshes, ponds) 
Urban/rural, 
agricultural (rice 
fields), natural 
wetlands associated 
with river deltas 
Urban/rural, 
agricultural, natural 
wetlands associated 
with the Salton sea 
lake 
Urban/rural, 
agricultural (rice-
fields), natural 
wetlands associated 
with river deltas 
Urban/rural 

[16] 

[17-20] 

[21] 

[22] 

Cx. pipiens s.l. 
Cx. salinarius 

Cx. pipiens s.l. 
Cx. tarsalis 

Cx. pipiens s.l. 
Cx. tarsalis 

Cx. pipiens s.l. 
Cx. modestus 

[23,24] 

Cx. pipiens s.l. 

N/A 

588 

2 705 994 

2 054 

1 807 000 

Monsoon 
influenced sub-
arctic climate 
Humid-sub-
tropical 

Urban (roadside 
ditches, catch basins) 

Urban (roadside 
ditches, catch basins) 

141 

167 830 

Cold semi-arid 

Urban/rural 

[25] 

[26] 

[27] 

Culex spp. 

Culex spp. 

Cx. tarsalis 

N/A 

N/A 

N/A 

* Information on land area and population estimates for 2019 were retrieved from https://www.census.gov/quickfacts/fact/table/US/PST045219 (for USA) and 
https://www.statistics.gr/el/demographic-data for Greece (2011 census data); **Information on budget was retrieved from official resources available online: 
a https://app.lla.state.la.us/PublicReports.nsf/11F8F448A601D7F2862582DB005B5770/$FILE/0001A355.pdf 
b https://www.fightthebite.net/wp-content/uploads/2019/10/symvcd-18ar.pdf 
c https://www.cvmosquito.org/sites/indiocacvm/files/uploads/2019_annual_report_final_0.pdf 
d http://www.pkm.gov.gr/default.aspx?lang=el-GR&page=160&proclid=2143 
e http://www.pkm.gov.gr/default.aspx?lang=el-GR&page=160&proclid=2142 

18 

 
 
TECHNICAL REPORT  

Vector control practice and strategies against West Nile virus 

Review of the case studies 
1. St. Tammany Parish case study 

Background 
St. Tammany Parish is located in the south-eastern corner of the state of Louisiana, USA, on the north shore of Lake 
Pontchartrain and is characterised by a humid sub-tropical climate. It comprises 2 190 km2 and has a population of 258 111. 
There are four major mosquito-producing habitats in the region: brackish and freshwater marshes, roadside ditches, woodland 
sloughs and creek beds, and thousands of artificial containers [16]. The first organised mosquito control efforts in the region 
began in 1968 and have expanded over the years to form what is known today as St. Tammany Parish Mosquito Abatement 
District (STPMAD). The district uses an integrated mosquito management plan with an annual budget of approximately USD 
8 000 000, involving mosquito surveillance activities, arbovirus surveillance, ground and aerial larviciding (biological, chemical), 
ground and aerial adulticiding, source reduction and public education. WNV was first detected in the region in 2002, resulting in 
increased enzootic transmission and human cases (40 cases in total by the end of the 2002 transmission season). In 
anticipation of the virus, the district decided to intensify surveillance and control measures and assess the impact of those 
measures in reducing WNV transmission intensity. This was done in collaboration with Tulane University of Tropical Medicine. 
Specific information on the methodology, results and conclusions of these studies is summarised below. 

Research objectives 
The objective of the study was to assess the impact of intensified larviciding and adulticiding vector control activities by 
surveying Culex spp. abundance, mosquito positive pools and sentinel chicken seroconversions for the 2002 WNV transmission 
season. Links with human cases were also made and compared with other regions in the state and previous years. 

Was WNV anticipated and what WNV surveillance methods were applied (if any)?  
The STPMAD performs routine WNV vector surveillance which includes (a) weekly/twice a week monitoring for mosquito 
abundance and WNV screening, (b) weekly monitoring of sentinel chicken seroconversion for WNV virus, and (c) wild bird 
surveillance. In 2002, WNV was anticipated in the study area and WNV activity was recorded in late May with the detection 
of a positive dead crow. Soon after the first human case was reported in early June, in parallel with the first positive 
mosquito pool, the virus spread rapidly throughout the region within a month, as evidenced by positive sentinel chickens, 
positive mosquito pools, dead bird reports and human cases. 

What WNV vector control interventions were applied?  
The St. Tammany Parish applied routine vector control activities and intensified the frequency of those activities in all regions 
in response to the elevated WNV transmission levels. Specifically, ground larviciding to roadside ditches was increased by 
46% compared to the 5-year average; ground and aerial ULV adulticiding treatments were increased by 63% and 450%, 
respectively, compared to the 5-year average. Ground ULV treatments were conducted with pyrethroid-based products, 
whereas aerial ULV treatments were conducted with an organophosphate-based product. 

Application timing of WNV control interventions (in response to WNV vector surveillance indicators, or/and 
in response to human cases) 
WNV management interventions were conducted and adjusted (intensified) in response to elevated vector abundance, 
clusters of dead American crows, elevated WNV mosquito infection rates, and human cases. The parish intensified their 
efforts in mid-March and sustained their larviciding activities for roadside ditches throughout the season. Following the first 
human cases and positive mosquito pool in June, ground ULV adulticiding and aerial ULV adulticiding were initiated and 
intensified for the remainder of the season. Ground ULV treatments targeted all accessible residential areas weekly, whereas 
locations for aerial ULV adulticiding were chosen based on positive mosquito pools, sentinel chicken seroconversions, dead 
bird reports and human cases. 

Efficacy evaluation of interventions 
The impact of ground and aerial adulticiding interventions was assessed by comparing weekly/monthly Culex abundance, 
and monitoring WNV in mosquito pools and sentinel chicken seroconversion across the 2002 season, before and after the 
onset of adulticiding treatments. Larval abundance indices were also calculated to assess the impact of larviciding 
interventions throughout the 2002 season. Furthermore, monthly adult and larval Culex abundance means from 2002 were 
compared with the five-year abundance mean for that period. 

Summary of outcomes 
Even though larviciding operations were intensified starting mid-March, WNV activity levels increased in early June and spread 
rapidly through the region. The intensive adulticiding treatments, following the first human case in June, in combination with the 
continuation of larviciding treatments resulted in a 10-fold reduction in Culex abundance between May and August. This 
reduction in abundance was not observed in the previous five years where no intensive interventions were applied (in contrast 
to the five-year monthly abundance means which remained fairly constant). Similarly, larval indices for the 2002 season showed 
an eight-fold decline, compared to the two-fold decline for the five-year average. The authors concluded that this rapid and 
widespread reduction in vector abundance contributed to a reduction in WNV transmission levels to humans, as evidenced by 
the subsequent reduction of human cases in August (this reduction was not observed in other parts of the state where 
transmission continued until December and where no intensified vector control was implemented). 

Strengths and limitations of research 
Vector control interventions were applied over large areas following standardised operational procedures. Use of both 
intervention and control (untreated) areas. Impact of treatment was assessed using multiple indicators (including mosquito 
infection rates and sentinel birds). Even though a reduction in human cases was observed in the region exposed to intensive 
interventions, this was not supported by statistical analysis.  

19 

 
 
 
Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

2. Sacramento-Yolo case study 

Background 
Sacramento and Yolo are two neighbouring counties located in the state of California in the middle of the Central 
Valley – the state’s single most productive agricultural region with a large variety of crops, including 46 000 acres = 
18 600 hectares of rice fields (P. Macedo, personal communication, 2 March 2020). The counties cover 5 122 km2 
and support a human population of 1 760 975. A major inland river delta formed by the Sacramento and San 
Joaquin Rivers is located on the south-west arm of Sacramento County, serving as an important habitat for 
important wildlife, such as native and migrating birds. The climate is Mediterranean, characterised by mild wet 
winters and hot dry summers. Mosquitoes have historically been a problem in the region due to the prolific water 
sources and suitable climate. For this reason, a state-funded vector control programme at district level was 
established in the area in 1946 and has been growing in resources and technical/scientific capacities since then. 
Currently, the district runs a contemporary integrated vector control programme throughout the year (2018 annual 
budget = USD 15 060 623), with a diverse and intensive vector surveillance network and a wide variety of vector 
control methods and products, while investing in operational research partnering with local universities and 
research institutes [28]. WNV was first detected in the counties in 2004 with low-level transmission to humans and 
horses. In 2005, a major outbreak occurred with 177 human infections, 40 equine cases, 16 900 dead birds, and 
53% seroconversion rate in sentinel chickens. WNV was anticipated in Sacramento County in 2005 and the district’s 
sensitive surveillance capacities allowed for early detection in birds and mosquitoes with subsequent interventions, 
depending on the response level designated by the California Mosquito-Borne Virus Surveillance and Response Plan 
[29]. The efficacy of those interventions was assessed by a team of researchers from different disciplines 
(entomology, veterinary medicine, public health, environmental science) from a large variety of institutes 
(Sacramento-Yolo Vector Control District, California Department of Public Health, Montana State University, 
University of California) and was described in two different manuscripts [17,18]. An additional assessment was 
conducted during the 2006 and 2007 WNV transmission seasons to provide additional data on control efficacy 
[19,20], as well as an assessment of the human health risk of adulticiding interventions [20]. Specific information 
on the methodology, results and conclusions of these studies are summarised below. 

Research objectives 
The objectives of the studies were to assess the impact of vector control applications in reducing incidence of 
human disease [17], abundance of Culex spp. and WNV infection rates [18] for the 2005 season. These two 
studies were conducted in parallel; one study assessed the impact on human disease and the other assessed the 
entomological impact of the same interventions on abundance and infection rates. Research was repeated in the 
same region during the 2006 [19] and 2007 WNV transmission seasons [20] when, in addition to assessing 
treatment effect on mosquito abundance and WNV infection rates, an assessment of the risk to human health of 
adulticiding was also conducted [20]. 

Was WNV anticipated and what WNV surveillance methods were applied (if any)? 
The Sacramento-Yolo mosquito control district performs routine WNV vector surveillance which includes (a) weekly 
monitoring for mosquito abundance and WNV screening, (b) weekly monitoring of sentinel chicken seroconversion 
for WNV virus, and (c) wild bird surveillance [28]. In 2005, WNV was anticipated in the study area and elevated 
WNV activity was detected before the onset of human cases in the form of clusters of dead birds, positive mosquito 
pools and chicken seroconversions. The same happened during the 2006 and 2007 season. The district had 
coordinated with aerial contractors in advance, and all administrative and regulatory processes were in place for 
immediate aerial adulticiding interventions in the event of elevated WNV transmission risk. 

What WNV vector control interventions were applied? 
The Sacramento-Yolo mosquito control district applied a sequence of control methodologies from their IVM plan 
[28] which included larviciding (biological, microbial and chemical), public education, and ground and aerial 
adulticiding treatments (ULV space sprays) with pyrethrin/pyrethroid based insecticides. 

Application timing of WNV control interventions (in response to WNV vector surveillance indicators, 
or/and in response to human cases) 
WNV management interventions were conducted and adjusted (intensified) in response to elevated vector 
abundance, clusters of dead American crows, elevated WNV mosquito infection rates and human cases. The 
combination of methods chosen and the intensity of their application (frequency, area coverage) were dependent 
on the risk level assigned to the region according to the state and local vector control plan. The district intensified 
their activities in March and sustained their larviciding and public education activities throughout the season, 
followed by ground ULV adulticiding efforts spot-treating regions with elevated mosquito infection rates. Despite 
the intensive larviciding, public education and ground adulticiding efforts, the district reached epidemic levels in 
late July/early August (the same pattern was observed in 2005, 2006, and 2007). The onset of human cases 
triggered the application of aerial ULV adulticiding using pyrethrin/pyrethroid-based insecticides over specific urban 
areas of the counties. Aerial treatments were conducted by professional contractors using modern aerial spray 
guidance technologies and a spray drift modelling system coupled with real-time weather recording for appropriate 
offset calculations. Despite a 60-year history of the aerial application of mosquito control products in California, this 
was the first instance in the state of aerial adulticiding over a large urban area. 

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Efficacy evaluation of interventions 
Larviciding, public education and ULV ground adulticiding were routinely conducted throughout the county in areas 
where virus activity was detected. In addition, aerial adulticiding ULV treatments were conducted in specific 
designated blocks, leaving plenty of unsprayed regions that could serve as control areas and allow for direct 
comparisons between treated and untreated regions. For this reason, all studies only allowed quantitative analysis 
of the aerial ULV adulticiding methodology. Carney and colleagues [17] quantified the impact of operational, large-
scale, aerial ULV interventions on human cases by comparing the proportion and incidence of cases in the treated 
(two treated blocks, North and South block) and untreated areas of Sacramento (the remainder of the county) in 
2005 before and after aerial treatments. Simultaneously that same year, Elnaiem and colleagues [18] quantified the 
impact of the same aerial treatments by comparing Cx. pipiens and Culex tarsalis abundance and WNV infection 
rates between treated (North Block) and untreated areas (the remainder of the county), before and after aerial 
treatments. In addition to pre- and post-trapping they used sentinel caged mosquitoes deployed within the spray 
zone under open field, semi-open field, and dense vegetation conditions to assess the efficacy of the treatment 
across different levels of exposure to the insecticide. Macedo and colleagues [19,20] repeated the evaluation of 
aerial ULV interventions during the 2006 and 2007 transmission season, applying the same evaluation approach 
followed by Elnaiem and colleagues [18], while further optimising the number and placement of trapping stations. 

Summary of outcomes 
During all three seasons (2005, 2006 and 2007) [18-20] aerial adulticiding interventions significantly reduced 
abundance (Cx. pipiens population reduction ranged from 40.8175%), and WNV infection rates in Culex spp. 
mosquitoes within the treatment areas. No such reductions were observed in untreated control areas where, on 
the contrary, an increase in abundance and infection rates was recorded. The assessment of the same 
interventions on human cases conducted by Carney and colleagues in 2005 [17], indicated that adulticiding 
reduced the number of human cases within the treatment sites compared to the untreated area of the county and 
that the odds of infection after spraying were six time lower in the treated areas than the treated ones. Barber and 
colleagues [30] conducted an economic cost analysis of the 2005 WNV outbreak in Sacramento county and 
concluded that only 15 WNV neuroinvasive cases would have to be prevented to make the emergency spray cost-
effective. The entomological line of evidence produced by Elnaiem and colleagues [18], together with the 
epidemiological line of evidence produced by Carney and colleagues [17] (two independent groups of researchers 
with different scientific backgrounds), confirm the conclusion that the aerial ULV adulticiding interventions were 
effective in disrupting the WNV transmission cycle and reducing human illness. The fact that these interventions 
were replicated for an additional two years with similar entomological outcomes (reduction in abundance and WNV 
infection rates) is strong evidence that, if applied appropriately, aerial ULV can measurably reduce the 
entomological indicators of WNV transmission activity, as well as the number of human WNV cases. Based on the 
risk assessment study, human risk from exposure to the ULV adulticiding applications was below regulatory levels 
of concern, and the risks from aerial ULV adulticiding are lower than those for ground (truck-mounted) ULV 
adulticiding [20]. 

Strengths and limitations of research 
Vector control interventions were applied over large areas following standardised operational procedures. Use of 
both intervention and control (untreated) areas. Impact of treatments was assessed using multiple indicators 
(including mosquito infection rates, sentinel birds, incidence of human cases). In addition to trapping in order to 
monitoring the abundance of wild mosquito populations, caged sentinel mosquitoes were used for direct 
assessment of insecticide toxicity and spray coverage. Observations were made over several seasons and 
experiments were replicated by different groups of researchers. In addition to efficacy, the human health risk of 
spraying interventions was also assessed. No major limitations were identified.  

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3. Coachella Valley case study 

Background 
Coachella Valley, characterised by a semiarid climate, is 25 km wide and extends north-westwards for 70 km from 
the Salton Sea (a shallow saline lake) through Riverside County to the San Gorgonio Pass, Southern California, 
USA. The Coachella canal, built in 1949, provides irrigation to approximately 388 km2 of productive agricultural 
land. The construction of the canal brought an abundance of water to the valley and benefitted the agricultural 
economy immensely, but at the same time resulted in the formation of mosquito larval habitats as a result of 
irrigation run-off. Due to the increasing mosquito nuisance and public health concerns, a mosquito control 
department was formed for the first time in 1951 to combat mosquitoes, in addition to the already active 
programmes for combatting eye gnats (Diptera: Chloropidae). Currently, vector control activities are conducted by 
the Coachella Valley Mosquito & Vector Control District with an annual budget of USD 10 849 764 (2019). Similar to 
Sacramento-Yolo, the district runs a contemporary integrated vector control programme throughout the year with a 
diverse and intensive vector surveillance network and a wide variety of vector control methods and products, while 
investing in operational research partnering with local universities and research institutes. Low level WNV enzootic 
transmission, but no human cases, was first detected in the valley during 2003 and seemed confined to the rural 
areas in the lower valley at the Salton Sea. The small wetlands associated with the north-eastern shore of the 
Salton Sea seem to be the early transmission/amplification foci for WNV, as well as other viruses (St. Louis 
encephalitis, Western equine encephalitis) in the region, with subsequent dispersal northward and upland away 
from the Salton Sea. In 2004, it was anticipated that WNV would occur in the region and this was detected during 
the district’s arbovirus surveillance activities. The unique topography of the region – with Salton Sea (early WNV 
transmission focus) at the extreme south-east corner of the valley (lower valley) and only one narrow corridor of 
wetlands and agriculture connecting this area to the rest of the valley (upper valley) – provided an opportunity to 
investigate whether intensive early mosquito control interventions, targeting early season virus amplification, could 
interrupt or delay amplification by limiting dispersal and subsequently prevent outbreaks of disease. To test this 
hypothesis, the University of California Davis, in collaboration with Coachella Valley Mosquito & Vector Control 
District, conducted a longitudinal study over three years (2004, 2005 and 2006) applying different strategies for 
vector control intervention [21]. Specific information on the methodology, results and conclusions of these studies 
is summarised below. 

Research objectives 
The objective of the study was to assess the impact of early season and late season vector control strategies on 
Culex spp. abundance, WNV infection rates and sentinel chicken seroconversions for the 2004, 2005 and 2006 
WNV transmission seasons. 

Was WNV anticipated and what WNV surveillance methods were applied (if any)? 
The Coachella Valley Mosquito & Vector Control District performs routine WNV vector surveillance which includes 
(a) weekly/bi-weekly monitoring for mosquito abundance and WNV screening, (b) bi-weekly monitoring of sentinel 
chicken seroconversion for WNV virus (discontinued as of 2016), and (c) wild bird surveillance (because of the low 
number of corvids present in the region very few birds are tested annually). In 2004 WNV was anticipated in the 
study area and WNV activity was detected before the onset of human cases through positive mosquito pools and 
chicken seroconversions, primarily confined to the lower valley near the Salton Sea. The same happened during the 
2005 and 2006. 

What WNV vector control interventions were applied? 
The Coachella Valley Mosquito & Vector Control District applied routine vector control activities, such as larviciding 
(biological, chemical), and public education. The arrival of WNV necessitated enhanced suppression, leading to 
ground and aerial adulticiding treatments (ULV space sprays) with pyrethroid insecticides reported in the study by 
Lothrop and colleagues [21]. Although larviciding operations were applied simultaneously at the study sites 
(including larviciding over the Salton Sea wetlands), the suppression levels achieved by those treatments alone was 
insufficient to prevent amplification and dispersal of the virus. 

Application timing of WNV control interventions (in response to WNV vector surveillance indicators, 
or/and in response to human cases) 
The study investigated the efficacy of single and combination adulticiding operations applied reactively (after the 
onset of human cases) and pro-actively (before the onset of human cases). Other routine vector control activities 
(i.e. larviciding) were conducted throughout the study region. Three vector control scenarios were tested across 
the three seasons, as described below.  

1.   In 2004, the virus was first detected in April, routine vector control was in place, and in addition, intensive 

ground ULV adulticiding treatment was conducted one month after initial detection of WNV.  
In 2005, the virus was detected in May – one month later than in 2004 – and spread rapidly across the valley. 
Routine vector control was in place, and in addition, ground and aerial ULV adulticiding was conducted in 
response to the elevated and widespread WNV transmission in May and June, respectively. 
In 2006, the virus was detected in April and, unlike the previous seasons, ground and aerial adulticiding was 
conducted almost immediately after first detection starting in late April and continued with consecutive 
treatments until early June (the emphasis was on aerial ULV with ground ULV filling in some limited areas). 

2. 

3. 

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Vector control practice and strategies against West Nile virus 

Efficacy evaluation of interventions 
The impact of ground and aerial adulticiding interventions was quantified by comparing Cx. pipiens and Cx. tarsalis 
abundance and WNV infection rates for treated and untreated (control) areas, before and after adulticiding 
treatments (sentinel mosquito cages and droplet spinners for collecting droplets were also used to monitor spray 
coverage). The wetland region on the southern shore of the Salton Sea was chosen as a control (untreated) area. 
Furthermore, vernal geometric means of Cx. tarsalis abundance were compared across the four years (20032006) 
with different vector control strategies. Application parameters of aerial adulticiding treatments (flight path and 
flight height) were improved in 2006, based on the knowledge gained in 2005, for better spray coverage and 
treatment precision. 

Summary of outcomes 
In 2004, despite the additional intensive ground adulticiding treatments in early spring (May), virus dispersal could 
not be prevented and eventually WNV was detected throughout the valley in positive mosquito pools and through 
chicken seroconversion, with human cases recorded in the urbanised upper valley. In 2005, the virus spread fast 
and could not be contained, but researchers were able to test and optimise the application parameters of ground 
and aerial adulticiding. Tests with caged sentinel mosquitoes indicated that landscape and wind can significantly 
affect the efficacy of these treatments on mosquito mortality and therefore repeated treatments are needed to 
overcome possible gaps in efficacy. In 2006, the almost immediate application in mid-April – upon detection of the 
first positive mosquito pools – of aerial adulticiding targeting the early transmission focus of Salton Sea resulted in 
a reduction of Cx. tarsalis abundance and WNV activity, as evidenced by the reduced WNV infection rates in 
mosquitoes and seroconversion rates in sentinel chickens. This reduction apparently delayed virus amplification and 
prevented tangential transmission in the urban areas of the upper valley, as evidenced by the absence of WNV 
detections by the human WNV surveillance network, and the absence of human cases. Furthermore, during 2003, 
2004 and 2005, without intensive adult control Cx. tarsalis vernal geometric means were significantly higher than 
in 2006, when intensive early adulticiding was conducted. These patterns were not observed in Cx. tarsalis 
populations from the control area, where Culex spp. abundance and WNV activity was greater in 2006 than in 
previous years. 

Strengths and limitations of research 
Vector control interventions were applied across large areas following standardised operational procedures. Use of 
both intervention and control (untreated) areas. Impact of treatments was assessed using multiple indicators 
(including mosquito infection rates and sentinel birds). In addition to trapping to monitor the abundance of wild 
mosquito populations, caged sentinel mosquitoes were used for direct assessment of insecticide toxicity and spray 
coverage. Observations were made over several seasons. This is the only study identified where aerial ULV 
adulticiding was applied proactively (before the onset of human cases). Even though no human cases were 
reported during the year of early and intensive interventions (compared to the previous years), this was not 
supported by statistical analysis.  

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4. Central Macedonia Region, Greece case study 

Background 
In 2010, a major WNV outbreak occurred in Central Macedonia, northern Greece. This was the first outbreak of 
WNV in the country and the second largest outbreak in Europe, with 197 neuroinvasive WNV disease cases and 25 
fatalities. The epicentre of the outbreak was located in the agricultural region of West Thessaloniki (the regional 
capital of Central Macedonia, with a population of 1.5 million people). This region is characterised by a 
Mediterranean climate and comprises significant natural wetlands, rivers, and ~20 000 hectares of rice-fields with 
prolific mosquito larval habitats [31]. Local vector control programmes funded by the state have been implemented 
in the region since 1997 (2019 annual budget = EUR 2 700 000). Before the introduction of WNV in the region, the 
only vector control approach targeting Culex populations was larviciding. As a result of the WNV threat, an 
exemption was issued for the first time in 2010 by the Ministries of Agriculture and Health to allow for aerial and 
ground ULV adulticiding using a pyrethroid-based product. The aerial ULV treatments were optimised locally for 
efficacy, precision, and non-target effects in a three-year longitudinal study (20082010) prior to receipt of the 
registrations [31,32]. During 2011, in anticipation of WNV, a group of scientists from European and US research 
institutes, in collaboration with local vector control authorities, set up a WNV vector and sentinel chicken 
surveillance network in the region to gauge virus activity and provide timely guidance and assessment of vector 
control interventions [22]. Specific information on the methodology, results and conclusions of these studies is 
summarised below. 

Research objectives 
Chaskopoulou and colleagues [22] aimed to evaluate the usefulness of a newly-established WNV surveillance 
network in providing early warning indicators for WNV activity and to assess the efficacy of vector control measures 
applied in response to those indicators. 

Was WNV anticipated and what WNV surveillance methods were applied (if any)? 
WNV was anticipated in the region and a WNV surveillance network was activated during 2011 using weekly 
mosquito trapping (for abundance indicators and WNV mosquito screening) and weekly monitoring of enzootic 
transmission through sentinel chicken seroconversions. 

What WNV vector control interventions were applied? 
The local vector control plan involved aerial larviciding (targeting rice-fields/flooded fields and natural wetlands), 
ground larviciding (targeting irrigating canals and other residential/urban breeding sites), and ground residual 
adulticiding with pyrethroid-based products (targeting public residential areas with high abundance of resting adult 
mosquitoes). In addition to these routine measures, an exemption was given in 2011 to allow for aerial ULV 
adulticiding applications in areas of increased WNV circulation. Aerial guidance technologies incorporated with 
spray fate/drift models were transferred from the US to allow for precise coverage of the target sites. 

Application timing of WNV control interventions (in response to WNV vector surveillance indicators, 
or/and in response to human cases) 
Routine larviciding and public outreach activities targeting agricultural, suburban and urban areas of the 
Thessaloniki region were initiated in May. Despite the routine vector control activities, WNV circulation levels 
increased significantly, leading to the first positive mosquito pool and chicken seroconversions in late June and the 
first reported human cases in late July. Decisions to apply aerial adulticiding were only made after the onset of 
human cases and treatments were conducted in August over the agricultural region of West Thessaloniki where 
high WNV activity was recorded across all surveillance systems. 

Efficacy evaluation of interventions 
Efficacy of aerial adulticiding treatments was evaluated by comparing Culex spp. abundance and sentinel chicken 
seroconversions before and after the treatments for treated (rural agricultural areas of West Thessaloniki) and 
untreated areas (rural areas of East Thessaloniki). 

Summary of outcomes 
Aerial ULV adulticiding interventions significantly reduced Culex spp. abundance (80% population reduction after 
treatments) and sentinel chicken seroconversion rates in the treated areas. No such reductions were observed in 
the untreated areas of the city, where, on the contrary, an increase in abundance was observed during the same 
period (44% increase), followed by an increase in chicken seroconversions. Culex spp. infection rates were too low 
to allow for comparisons. 

Strengths and limitations of research 
Vector control interventions were applied over large areas following standardised operational procedures. Use of 
both intervention and control (untreated) areas. Impact of treatment was assessed using multiple indicators 
(including mosquito infection rates, sentinel birds). Prior to operational treatments, spray applications were tested 
for efficacy and non-target impact in a three-year longitudinal study. Unfortunately, due to the low number of 
positive mosquito pools, impact on vector infection rates could not be determined.  

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Vector control practice and strategies against West Nile virus 

5. The North-Central Texas case study 

Background 
During 2012, Texas, USA, experienced a major WNV outbreak, with neuroinvasive disease incidence at least 1.6 
times higher than any previous year since WNV disease cases were first reported in the state in 2002. Forty-two 
percent of the reported cases was concentrated in four adjacent Texas Counties: Collin, Dallas, Denton and Tarrant 
(an area 7 112 km2 with a population of 5 700 000). The climate of the area is humid and sub-tropical and the 
2012 epidemic year was considered a high outlier in terms of winter temperature, total rainfall in winter and early 
spring, and summer heat. There is no centralised county-based vector control at district level; nonetheless, 
surveillance and contract-specific vector control operations are conducted in coordination with local health 
departments and municipalities. In response to the outbreak in these four counties, surveillance and control 
activities were stepped up. The surveillance efforts and efficacy assessment of these interventions is described in 
two different manuscripts [23,24]. The impact of aerial adulticiding applications on the incidence of emergency 
department visits in Dallas (main concerns: skin rash and respiratory distress) was also assessed [24]. Specific 
information on the methodology, results and conclusions of these studies is summarised below. 

Research objectives 
The objective of Ruktanonchai and colleagues [23] was to assess the impact of vector control applications in 
reducing incidence of human disease using data from all four counties. Chung and colleagues [24], in parallel with 
Ruktanonchai and colleagues [23], closely monitored WNV transmission activity in vectors in one of the four 
counties (Dallas), with the aim of investigating whether a vector index could be used to predict the onset of human 
cases. Furthermore, the impact of aerial adulticiding on human health was evaluated in Dallas [24]. 

Was WNV anticipated and what WNV surveillance methods were applied (if any)? 
WNV activity has been recorded in the region since 2002 and activity was expected. A dense WNV vector 
surveillance network, with weekly trapping of adult mosquitoes, was put in place from May until December in 
Dallas County. No information on the other three counties is reported in the published manuscripts. 

What WNV vector control interventions were applied? 
In response to increased WNV transmission levels, ground larviciding and ground ULV adulticiding were conducted 
in July. Due to the continuous increase in human cases, a decision was made to perform aerial ULV adulticiding in 
August. 

Application timing of WNV control interventions (in response to WNV vector surveillance indicators, 
or/and in response to human cases) 
All vector control activities were conducted in response to human cases. A significant increase in vector index was 
recorded in Dallas County early in the season, but adulticiding interventions were conducted and intensified only 
after the increase in human cases. 

Efficacy evaluation of interventions 
 Efficacy of aerial adulticiding interventions, conducted in two out of the four counties, was evaluated by calculating 
incidence rate ratios (IRRs) in treated (Dallas and Denton) and untreated (Collin and Tarrant) counties by 
comparing incidence before and after aerial spraying. 

Summary of outcomes 
 Aerial ULV adulticiding implemented for WNV control was associated with a reduction in WNV neuroinvasive 
disease. WNV neuroinvasive disease incidence before and after spraying was 7.3/100 000 population and 
0.28/100 000 population, respectively; the IRR was 26.42. In untreated areas, the before and after incidence was 
4.8/100 000 population and 0.45/100 000 population, respectively; the IRR was 10.57. As expected, given that 
aerial spray events were conducted late during the outbreak, disease incidence decreased during the post-spray 
period in both treated and untreated areas. However, the relative change was significantly greater in areas sprayed 
aerially. Furthermore, aerial ULV adulticiding was not associated with increases in emergency department visits for 
respiratory symptoms [24]. 

Strengths and limitations of research 
Vector control interventions were applied over large areas following standardised operational procedures. The 
direct efficacy of insecticide interventions in reducing incidence of human disease was assessed by comparing 
clinical case distribution within treated and untreated control areas. However, the impact of interventions on vector 
population was not assessed. 

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6. Chicago case study 

Background 
WNV cases were first reported in the state of Illinois, USA, in 2002, with 884 human cases [6], 80% of which were 
reported from the Chicago metropolitan region in seven urban counties: Cook, DuPage, Kane, Kendall, Lake, 
McHenry, and Will. Transmission continued in the following years, and from 2002 through 2009, a total of 321 
human cases were reported in the city of Chicago (urban environment, monsoon influenced sub-arctic climate, 
population of 2 716 000). In anticipation of WNV transmission in 2005, the city of Chicago responded with ground 
ULV adulticiding applications, targeting areas with high mosquito infection rates [25]. Specific information on the 
methodology, results and conclusions of these studies is summarised below. 

Research objectives 
To assess the impact of ground ULV adulticiding applications during the 2005 WNV transmission season by 
monitoring abundance and WNV infection rates of Culex spp. before, during and after adulticiding treatments in 
Cook County, Chicago. The authors investigated whether sequential adulticiding treatments had an additive effect 
and compared efficacy depending on the number of treatment rounds, ranging from zero to four treatment rounds. 

Was WNV anticipated and what WNV surveillance methods were applied (if any)?  
WNV was anticipated and WNV vector surveillance was in place, with weekly trapping of adult Culex spp. from April 
until September. 

What WNV vector control interventions were applied? 
Ground ULV adulticiding treatments with pyrethroid insecticides were conducted by professional contractors. Large 
blocks (80.9159.4 km2) in northern and southern parts of the county received treatments. Four sequential 
treatment rounds were applied across the season. Non-sprayed areas of the county were used as control sites. 

Application timing of WNV control interventions (in response to WNV vector surveillance indicators, 
or/and in response to human cases) 
Measures were applied in response to Culex spp. abundance and infection rates. Study sites were chosen on the 
basis of persistent WNV-positive mosquitoes. 

Efficacy evaluation of interventions 
Efficacy was assessed by comparing mosquito density changes and WNV infection rates in mosquitoes pre and post 
treatments and across treated and control areas. 

Summary of outcomes 
Significant Culex population reductions were observed post ULV treatments. Specifically, two sequential ULV 
treatments decreased mosquito abundance by 54%, whereas mosquito abundance increased by 153% in the non-
sprayed areas. Overall, the highest reduction in mosquito populations was observed at sites receiving four 
sequential treatments. However, Maximum Likelihood Estimates (MLE) of WNV minimum infection rates varied 
widely across treated and untreated areas and no evidence of a significant effect of adulticide treatments on 
minimum infection rates was found. 

Strengths and limitations of research 
Vector control interventions were applied over large areas following assessment using multiple indicators (including 
mosquito infection rates). Different treatment scenarios (single versus serial applications) were tested. According to 
the authors, the study was conducted during an unusually hot and dry summer season that may have lessened the 
impact of the treatments.  

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7. Atlanta case study 

Background 
Since the introduction of WNV in Georgia, USA, in 2001, a total of 473 humans cases have been reported [6]. In 
Atlanta, the capital and most populated city in the state, WNV cases are uncommon, nonetheless surveillance and 
control activities in response to WNV are most intensely conducted in the most epidemiologically relevant counties, 
of Dekalb and Fulton (population of 1 807 114, humid sub-tropical climate). Vector surveillance and control services 
are provided by local health departments and/or private contractors. The main vector control strategy applied in 
both counties is larviciding treatments on roadside catch basins from late June until October in an attempt to 
control WNV transmission. When WNV positive pools are detected, neighbourhood outreach campaigns are 
performed near the detected infections and larviciding is intensified within a buffer distance around the WNV 
infection location. Neither county has budget to monitor efficacy of larviciding operations in larval or adult 
populations. To address this knowledge gap, McMillan and colleagues [26] performed a study to assess the impact 
of these strategies on WNV transmission level during the 2015 and 2016 season. Specific information on the 
methodology, results and conclusions of these studies is summarised below. 

Research objectives: Given the lack of information about the population-level impact of larviciding, McMillan and 
colleagues [26] aimed to quantify the impact of larviciding catch basins on Culex spp. adult female abundance and 
WNV infection prevalence in urban environments of Atlanta, Georgia. 

Was WNV anticipated and what WNV surveillance methods were applied (if any)?  
WNV was anticipated in the region and WNV vector surveillance activities were in place via weekly trapping 
(starting April/March and continuing for the duration of the study) to calculate Culex spp. abundance indices and 
WNV infection rates. 

What WNV vector control interventions were applied?  
Larviciding applications targeting catch-basins were the only method applied. A combination of larviciding products 
were used in accordance with label instructions. 

Application timing of WNV control interventions (in response to WNV vector surveillance indicators, 
or/and in response to human cases) 
Two different application timing scenarios were tested across the two consecutive years. (1) In 2015, larvicides 
were applied during the epidemic period of WNV (JulySeptember) following larviciding timing similar to routine 
spray applications of Fulton and DeKalb. (2) In 2016, larvicides were applied at the beginning of Culex spp. 
breeding season in Atlanta (MarchMay). Larvicides were applied weekly or bi-weekly according to manufacturer’s 
label instructions for each product. 

Efficacy evaluation of interventions 
Four sites (urban parks) were used for the analysis (two were assigned as treatment sites and two as untreated 
control sites). Efficacy of treatments was assessed by (a) comparing abundance of larvae, pupae and resting adults 
associated with a sub-set of the treated catch basins before, during and after the applications in comparison with 
abundance data from an equivalent sub-set of untreated (control) catch basins; (b) comparing abundance of Culex 
spp. trapped in treated versus untreated areas before, during and after the applications, in an attempt to link larval 
productivity to adult population collections, and (c) comparing WNV minimum infection rates in adult Culex spp. 
(from both catch basins and traps) in treated and untreated areas before, during and after treatments. 

Summary of outcomes 
Larviciding in catch basins resulted in more than 90% reduction in larval/pupal collections in treated sites. Even 
though larvicides were effective in suppressing larval and pupal populations, no significant reduction was observed 
in adult Culex spp. collected with traps in the proximity of the treated catch basins or in adults collected resting in 
catch basins. In addition, WNV infection prevalence between treated and untreated sites was similar. The authors 
conclude that, on the scale and frequency applied in this study (0.210.37 km2 study sites, spray periods 814 
weeks), larval control alone may not lead to meaningful reductions in adult populations and WNV prevalence. 

Strengths and limitations of research 
Vector control interventions were applied following standardised operational procedures. Use of both intervention 
and control (untreated) areas. Impact of treatments was assessed using multiple indicators (including mosquito 
infection rates). Observations were made over several seasons. Despite the fact that the control strategy followed 
by the authors was pre-specified in terms of spatial extent and approach to mimic operational interventions, a 
larger spatial coverage would have possibly resulted in greater impact. 

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8. Fort Collins case study 

Background 
WNV cases were first reported in the state of Colorado, USA, in 2002 and since then human cases have been 
reported every year, accumulating to a total of 5 526 cases as of 2018 [6]. Fort Collins serves as the seat of 
Larimer County, which is one of the counties with consistent WNV circulation. In 2017, a team of researchers from 
USA and European institutions developed and tested under laboratory conditions an endectocide-treated feed as a 
systemic endectocide (an antiparasitic drug that is active both against endoparasites and ectoparasites) for birds to 
target blood-feeding Cx. tarsalis [27]. Ivermectin was the most effective endectocide and showed strong potential 
in laboratory studies. In order to assess the potential of the treatment under field conditions, the authors 
performed a small-scale field study in urban and suburban areas of Fort Collins during the 2017 WNV transmission 
season [27]. Specific information on the methodology, results and conclusions of the field study is summarised 
below. 

Research objectives 
The efficacy of the new IVM-treated bird feed in reducing Culex abundance and WNV infection rates was tested 
under field conditions. Furthermore, the impact of the treatment on the health of the local fauna was investigated. 

Was WNV anticipated and what WNV surveillance methods were applied (if any)? 
WNV was anticipated and a WNV surveillance network with weekly monitoring of vector abundance and infection 
rates had been in place since 2006. 

What WNV vector control interventions were applied?  
Field sites in areas with historically high WNV circulation levels were treated with ivermectin-treated bird feed 
stations. The ivermectin-treated bird feed was used at a concentration that proved to be the most effective 
(greater than 80% mortality on Cx. tarsalis mosquitoes) and safe under laboratory conditions (chickens and wild 
Eurasian collared doves exhibited no signs of toxicity when feeding on this concentration). Six sites were chosen in 
suburban/urban open areas of east Fort Collins (three treated and three untreated control sites). At each site, an 
array of three bird feed stations was placed in an approximately triangular pattern around a mosquito trap at a 
distance of 50 m. The feed was changed daily to account for any ivermectin degradation effects due to 
environmental exposure. Motion-activated trail cameras were used to document bird visits to the feeders, and 
blood samples from wild birds were collected for ivermectin detection and quantification. 

Application timing of WNV control interventions (in response to WNV vector surveillance indicators, 
or/and in response to human cases) 
Field treatments commenced in early June and lasted until early September in areas with high WNV circulation. 

Efficacy evaluation of interventions 
The efficacy of the ivermectin-treated bird feed stations in reducing WNV transmission levels was evaluated by (a) 
comparing Culex abundance between control and treated sites; (b) comparing Culex abundance between treated 
sites and historical data from the same sites for the period 20062016 (years without treatment), and (c) 
comparing WNV infection rates and the number of WNV-positive pools between treatment and control sites. 

Summary of outcomes 
Nearly all birds captured and tested around the treated bird feeders had detectable levels of ivermectin in their 
blood (87% of the tested sera was positive for ivermectin). However, entomological data showed that WNV 
transmission was not reduced around the treated bird feeders. Culex spp. abundance was similar between treated 
and untreated sites and between treated and untreated seasons. No significant difference was observed in the 
number of positive mosquito pools. 

Strengths and limitations of research 
This a proof of concept study assessing the impact of a novel control approach against vector abundance and 
infection rates. Although the scale of field interventions may have been too small to have an effect on vector 
abundance and infection rates, given the pilot nature of the study, this information will be valuable in informing 
future large-scale trials.  

28 

 
 
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Table 6. Detailed information on WNV vector management experience presented by case study 

Timing of interventions 

Efficacy evaluation (Culex spp.) 

Impact on WNV circulation levels 

Case 
Studies 

1. St. 
Tammany 
Parish, LA, 
USA [16] 

Types of 
interventions 

Intensive larviciding in 
combination with 
ground and aerial ULV 
adulticiding 

2. 
Sacramento 
and Yolo 
Counties, CA, 
USA [17-20] 

- Intensive larviciding 
and public education. 

- Ground ULV 
adulticiding. 

- Aerial ULV 
adulticiding. 

2002 season 

- Intensive larviciding since March (46% 
increase compared to the five-year 
average). 

- Initiation of ground and aerial ULV 
adulticiding in June following the first 
human case (63% and 450% increase, 
respectively, compared to the five-year 
average). 

- Comparing adult mosquito abundance, infection 
rates, chicken seroconversions before and after 
adulticiding treatments across the season. 

- Comparing mosquito larval abundance before and 
after larviciding treatments across the season. 

- Comparing monthly adult and larval mosquito 
abundance means from 2002 with the five-year 
abundance average for that period.  

2005, 2006, 2007 seasons 

2005, 2006, 2007 seasons 

- Intensive larviciding and public education 
since March. 

- Initiation of ground ULV adulticiding 
June-July (in response to infection rates). 

- Aerial ULV adulticiding late July-August 
(in response to human cases). 

- Mosquito abundance, infection rates and chicken 
seroconversions were used to monitor overall 
efficacy of control operations across the season. 
For larviciding/public education no control area was 
available (all areas with WNV activity were treated). 
Non-treated areas were available for aerial ULV 
adulticiding treatments, allowing for additional 
comparisons between treated and untreated blocks 
(pre- and post-trapping, sentinel cages). 

2005 season 

- Aerial ULV adulticiding impact on human cases 
was quantified by comparing proportion and 
incidence of human cases between treated and 
untreated blocks. 

- Comparing adult mosquito abundance and WNV 
infection rates between treated and untreated 
(control) areas, before and after ground and aerial 
ULV adulticiding treatments. 

- Geometric means of adult mosquito abundance 
were compared across four years (20032006) 
with different vector control strategies. 

3. Coachella 
Valley, CA, 
USA [21] 

- Routine larviciding. 

- Ground ULV 
adulticiding and aerial 
ULV adulticiding 
(singly or in 
combination). 

- Routine larviciding was conducted for all 
three seasons from early spring. 

- 2004 season: intensive ground ULV 
adulticiding started in June. 

- 2005 season: ground and aerial ULV 
adulticiding started in June and July, 
respectively, in response to human cases. 

- 2006 season: Early (April) aerial ULV 
adulticiding (with some spot ground ULV 
treatment) in response to positive 
mosquitoes. 

(circulation in mosquitoes, enzootic circulation, human cases) 

- Despite the early intensification of larviciding operations in March, WNV 
circulation levels increased in early June and spread rapidly across the region. 

- Larval abundance indices showed an eight-fold decline against the five-year 
average two-fold decrease. 

- Adulticiding treatments in combination with larviciding treatments resulted in a 
10-fold reduction in Culex abundance from May to August. This reduction was not 
observed in the five-year average abundance curves, which in contrast remained 
constant. 

- Rapid decrease in human cases in August followed the rapid decline of Culex 
populations (this pattern was not observed in other regions of the state). 

- Despite the intensive larviciding, public education and ground adulticiding efforts 
(for three consecutive years) the district reached epidemic levels in late July/early 
August (as evidenced by high infection rates, chicken seroconversions and human 
cases). 

- Evidence for all three seasons (2005, 2006, 2007) indicated that aerial 
adulticiding interventions significantly reduced abundance, WNV infection rates 
and positive mosquito pools of Culex spp. mosquitoes within the treatment areas. 

- Evidence from the 2005 season indicated that aerial ULV adulticiding reduced 
the number of human cases within the treatment sites compared to the untreated 
sites and that the odds of infection after spraying were six times higher in the 
untreated areas compared to the treated ones. 

2004 season: Despite routine larviciding and additional intensive ground 
adulticiding treatments in early spring, WNV dispersed throughout the valley as 
evidenced by positive mosquito pools, chicken seroconversions and human cases. 

2005 season: Interventions were conducted late and virus could not be contained 
but allowed for optimisation of aerial adulticiding methods. 

2006 season: 

- Aerial ULV adulticiding treatments resulted in significant reductions of adult 
abundance and WNV activity, as evidenced by the reduced WNV infection rates in 
mosquitoes and seroconversion rates in sentinel chickens post-treatment. 

- Geometric abundance means in 2006 were significantly lower than in 2003, 
2004, and 2005 seasons when early adulticiding was not conducted. 

These patterns were not observed in adult mosquito populations from the control 
area, where Culex sp. abundance and WNV activity was greater in 2006 than in 
previous years. 

29 

TECHNICAL REPORT 

Vector control practice and strategies against West Nile virus  

4. Central 
Macedonia 
Region, 
Greece [22] 

5. North 
Central Texas 
(Collin, 
Dallas, 
Denton, 
Tarrant 
Counties) TX, 
USA [23,24] 
6. City of 
Chicago, IL, 
USA [25] 

7. Atlanta 
(Dekalb and 
Fulton 
Counties), 
GA, USA [26] 

Case 
Studies 

Types of 
interventions 

Timing of interventions 

Efficacy evaluation (Culex spp.) 

Impact on WNV circulation levels 

- Routine ground and 
aerial larviciding 
targeting 
urban/suburban and 
rural/agricultural 
areas, respectively. 

- Aerial ULV 
adulticiding. 

- Ground larviciding 
and ground ULV 
adulticiding. 

- Aerial ULV 
adulticiding. 

2011 season 

- Routine control treatments were initiated 
in May. 

- Despite the detection WNV circulation in 
late June (mosquitoes, sentinel chickens) 
aerial ULV was conducted in August in 
response to human cases. 

2012 season 

- Ground larviciding and adulticiding were 
applied in response to increased WNV 
circulation in July. 

- Aerial ULV adulticiding was applied in 
response to human cases in August. 

(circulation in mosquitoes, enzootic circulation, human cases) 

- Comparing adult mosquito abundance and 
sentinel chicken seroconversions before and after 
the treatments between treated (rural areas of 
West Thessaloniki) and untreated areas (rural 
areas East Thessaloniki). 

- Aerial ULV adulticiding interventions significantly reduced Culex spp. abundance 
and sentinel chicken seroconversion rates within the treatment areas. 

- No such reductions were observed in the untreated areas of the city where, on 
the contrary, an increase in abundance was observed immediately post-treatment 
followed by an increase in chicken seroconversions. 

- Aerial ULV adulticiding impact on humans cases 
was evaluated by calculating incidence rate ratios 
(IRRs) in treated (Dallas, Denton) and untreated 
(Collin, Tarrant) counties by comparing incidence 
before and after aerial spraying. 

- Aerial ULV adulticiding was associated with a reduction in WNV neuroinvasive 
disease. Given that aerial spray events were conducted late during the outbreak, 
disease incidence decreased during the after spray period in both treated and 
untreated areas. However, the relative change was significantly larger in areas 
sprayed by air. 

Ground ULV 
adulticiding (single, 
versus sequential 
applications) 

2005 season 

- Treatments were conducted in July-
August in areas with high WNV infection 
rates in mosquitoes. 

- Comparing adult mosquito abundance pre and 
post treatments and across treated and control 
areas. 

Larviciding applications 
targeting catch-basins. 

Two different timing scenarios were 
tested: 

- 2015 season: larvicides were applied 
during the epidemic period of WNV 
(JulySeptember). 

- 2016 season: larvicides were applied at 
the beginning of Culex spp. breeding 
season (MarchMay). 

- Comparing abundance of mosquito larvae, pupae 
and resting adults associated with treated catch 
basins before, during and after treatments in 
comparison with abundance data from untreated 
(control) catch basins. 

- Comparing adult mosquito abundance trapped in 
treated versus untreated areas before, during and 
after the applications, in an attempt to link larval 
productivity to adult population collections. 

- Comparing WNV infection rates in adult 
mosquitoes (from both catch basins and traps) in 
treated and untreated areas before, during and 
after treatments. 

- Significant Culex population reductions were observed post ground ULV 
treatments. Specifically, two sequential ULV treatments decreased mosquito 
abundance by 54%, whereas mosquito abundance increased by 153% in the non-
sprayed areas. 

- The highest reduction was observed at the trap sites receiving four sequential 
treatments, indicating that serial treatments are more effective than single 
applications. 

- WNV minimum infection rates varied widely across treated and untreated areas, 
indicating that ground adulticide treatments had no direct effect on WNV infection 
rates. 

- More than 90% reduction in larval/pupal collections in treated catch basins was 
recorded. 

- No significant reduction was observed in adult Culex spp. populations collected 
with traps in proximity to treated catch basins or in adults collected resting in 
catch basins. 

- WNV infection prevalence between treated and untreated sites was similar. - On 
the scale and frequency applied in this study, larval control alone did not lead to 
meaningful reductions in adult populations and WNV prevalence. 

8. Fort 
Collins, CO, 
USA [27] 

- Ivermectin-treated 
bird feed stations. 

2017 season 

- Field treatments commenced in early 
June and continued until early September 
in areas with high circulation of WNV. 

- Comparing adult mosquito abundance between 
control and treated sites. 

- Birds captured and tested around the treated bird feeders had detectable levels 
of ivermectin in their blood. 

- Comparing adult mosquito abundance between 
treated sites and historical data from the same 
sites from 2006-2016 (no treatment years). 

- Comparing WNV infection rates/number of WNV-
positive pools between treatment and control sites. 

- Culex abundance was similar between treated and untreated sites and between 
treated and untreated seasons. 

- No significant difference was observed in the number of positive mosquito pools 
between treated and untreated sites. 

30 

 
 
Vector control practice and strategies against West Nile virus  

TECHNICAL REPORT 

4. Discussion 

West Nile virus vector surveillance and management 
capacities in Europe 

Through the survey administered to European national/regional state agencies involved in vector control 
operations, we were able to get an overview of the WNV vector surveillance and control activities in the EU/EEA, 
ENP partner and EU candidate/potential candidate countries. We also identified some of the major challenges 
related to the implementation of WNV management strategies. The majority of EU/EEA, ENP partner and EU 
candidate/potential candidate countries implement at least one method of WNV surveillance (Figure 15 top panel). 
The most common passive WNV surveillance method is the detection of human cases, followed by surveillance of 
dead animals. The most common method of active WNV surveillance is mosquito screening, followed by sentinel 
bird screening and sentinel equid screening for EU/EEA and ENP partner and EU candidate/potential candidate 
countries, respectively. Even though a large majority of countries perform routine vector surveillance (abundance 
monitoring), less than 50% of these countries perform mosquito screening for WNV. Furthermore, a much lower 
percentage (<15%) of countries perform insecticide resistance testing, and even in those cases it is not 
implemented systematically. The main challenge identified by respondents in relation to implementation and 
continuity of WNV surveillance methods is the lack of funding, alongside the shortage in human resources. 

The majority of EU/EEA countries that do not implement any type of WNV vector control method have no history of 
autochthonous WNV human cases, indicating that the primary cause of the absence of control measures is the 
absence of WNV risk. A small percentage of ENP partner and EU candidate/potential candidate countries (17%) 
reported an absence of control measures against WNV vectors. However, due to the low response rate from ENP 
partner countries, this percentage may not be representative of the entire region. 

31 

 
 
Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

Figure 15. Maps depicting the number of WNV vector surveillance and control methods applied per country 

32 

 
 
 
 
TECHNICAL REPORT 

 Vector control practice and strategies against West Nile virus 

Among the EU/EEA countries that implement vector control, the most widely adopted method by far is biological 
larviciding, while the least adopted method is source reduction through environmental management. Among ENP 
partner and EU candidate/potential candidate countries, public education followed by biological larviciding, 
chemical larviciding, and LV surface spraying adulticiding are the most widely methods applied. The high adoption 
rate of biological larviciding across EU/EEA countries, which is not observed in ENP partner and EU 
candidate/potential candidate countries, is probably a result of the dominance of Bacillus active ingredients in the 
EU/EEA mosquito control market. This can be concluded from the responses to Questions 9 and 13, where EU/EEA 
respondents identified the limited number of registered biocidal products (biological, chemical) as the most 
important barrier towards effective vector control strategies. In fact, many of the respondents declared that only 
one biological larvicide was available, at high cost and with limited residual efficacy, affecting the sustainability of 
their larviciding operations. The respondents further stressed the need for a wider range of products and active 
ingredients to manage the increasing problem of pesticide resistance. Another important constraint identified was a 
complex regulatory framework that does not cater to environments with a high level of complexity and vector 
abundance. 

Larviciding interventions (in any form) appear to be performed proactively in the various EU/EEA countries/regions, 
since the vast majority of programmes apply these methods in response to vector abundance data (larval 
densities). ULV adulticiding treatment is generally triggered by the occurrence of autochthonous WNV human cases 
among EU/EEA countries, with less than 50% of the respondents applying these methods in response to high 
infection rates in mosquitoes or sentinel animals. This method is therefore primarily used as an emergency, 
reactive response measure. The main flaw in this reactive approach is that by the time the first case is confirmed, 
WNV has already been amplified to epidemic levels in birds and mosquitoes and is therefore more difficult and 
costly to contain. When adequately implemented, some of the most effective WNV surveillance methods that are 
currently applied in several European countries (e.g. mosquito/sentinel animal screening) can provide warnings 
several weeks in advance of human cases. Therefore these methods should be used to support decision-making on 
when and where to deploy vector control (including adulticiding) to prevent or minimise the occurrence of human 
infections. ENP partner and EU candidate/potential candidate countries appear to apply all available vector control 
methods (including adulticiding) routinely in response to vector abundance data. 

Finally, when asked whether they need vector control guidelines >84% of the countries responded ‘yes’, indicating 
that there is currently a need for more guidance on how to mitigate the threat posed by WNV. 

West Nile virus vector management - what is the evidence of 
effect on epidemiological parameters? 

In the absence of an effective vaccination for humans, vector control remains the primary line of defence in 
preventing and containing WNV outbreaks [5]. An integrated vector management (IVM) strategy utilises the 
appropriate combination of vector surveillance tools to guide vector control interventions at the right time and 
place, in response to WNV entomological/enzootic circulation indicators in order to reduce or even prevent WNV 
outbreaks [5,10,33]. An IVM strategy relies on a rational combination of effective and ecologically sound vector 
control methods (every method has its limitations by default and to help balance these limitations, a synergy of 
methods is often required) in a specific operational context, to reduce and sustain vector populations below 
thresholds where WNV transmission to humans is infrequent [10]. Integrated vector control is the most sound and 
comprehensive strategy for combating mosquito-borne diseases, however, there is currently limited evidence on 
the impact of IVM programmes in preventing WNV outbreaks. 

Direct evidence from nine different studies, conducted by eight different groups of independent researchers in five 
different geographical regions indicates that targeted, surveillance-based aerial ULV adulticiding treatments can 
effectively reduce WNV circulation levels. Two of these studies [17,23] provide direct evidence that this vector 
control method is effective in disrupting the WNV transmission cycle and in reducing human illness at urban sites. 
One study provided evidence that ground ULV adulticiding can reduce abundance of vector populations, however, 
this reduction was not reflected in a reduction of WNV infection rates in Culex mosquitoes. In four case studies 
conducted in the context of an organised, central, integrated vector control programme (funding capacities ranging 
from USD 1.931.4 per capita), WNV was anticipated and early preventive measures were applied including 
intensive larviciding and public education. However, in all four case studies, WNV amplification could not be 
prevented, as evidenced by high infection rates in mosquitoes, and/or high seroconversion rates in sentinel 
animals, and also human cases. Adulticiding was not included in the prevention strategy and was only implemented 
after the onset of human cases. 

Only one study was identified that aimed to link larval reduction (in catch basins exposed to regular larviciding 
treatments) to WNV prevalence in adult Culex mosquitoes [26], but no difference was observed between treated 
and untreated sites. Moreover, no link could be made between larval reduction and reduction of adult female 
mosquito populations within treatment sites. The scale of the treatments may have been too small, or the presence 
of larval habitats outside of and within the boundaries of the treatment sites may have limited efficacy estimates of 

33 

 
Vector control practice and strategies against West Nile virus 

TECHNICAL REPORT 

larviciding in this study. Cx. pipiens adults are reported to travel for up to 1.5 km/night [34]. This, in combination 
with the evidence produced by McMillan and colleagues [26], indicates that the peri-domestic strategy of escalating 
vector control measures within a buffer of 200500 m around a WNV human case, commonly applied in some 
European regions/countries [11], may not be sufficient to reduce transmission of WNV. 

During the last decade, vector control research in Europe has been focusing on invasive mosquito species and in 
particular on Ae. albopictus. One study was identified [15] that, even though primarily designed to target Ae. 
albopictus, reported efficacy against adult Cx. pipiens populations in an urban environment: Caputo and colleagues 
[15] investigated the effects of operational larviciding interventions on road-side catch basins in combination with 
LV adulticiding against adult mosquito populations (two methods commonly applied in Italy) and reported 
significant reduction in both adult Ae. albopictus and Cx. pipiens populations in the treated areas. The authors 
could not determine whether the synergy of the two methods or adulticiding alone was responsible for the control 
levels achieved and concluded that the relative role of adulticides and larvicides should be investigated separately. 
Overall, it is clear that the impact of operational larviciding on wild adult Culex populations and WNV epidemiology 
remains largely understudied [14,26]. 

There is currently evidence that intensive mosquito-adulticiding efforts, applied once a WNV outbreak has started, 
can interrupt virus transmission and prevent human cases. However, evidence of vector control interventions 
preventing WNV outbreaks from occurring is limited and additional research under operational conditions is needed 
to better inform public health policy decisions relating to optimum vector control strategies for WNV management. 

Limitations of the methodology 

The results are representative only for those countries that responded to the questionnaire. One of the limitations 
of the survey is that it focused on national capacities of WNV surveillance and control, ignoring the intra-country 
variations that may be significant. The scoping literature review is not an exhaustive review and there may be 
studies (particularly in languages other than English) that were not detected. 

34 

 
 
 
 
TECHNICAL REPORT 

 Vector control practice and strategies against West Nile virus 

5. Conclusions and recommendations 

This report reviewed the WNV surveillance and control activities implemented in the EU/EEA, the EU candidate and 
potential candidate countries and ENP partner countries and collated existing evidence on the effectiveness of 
vector control practices in reducing WNV risk. The main conclusions are listed below. 

  WNV surveillance and control activities are implemented in the majority of countries with a history of WNV 

 

 

 

transmission to humans and animals. 
Consistent WNV surveillance is the driver for vector control decisions and needs to be reinforced and acted 
upon. 
Source reduction and public education campaigns are essential vector control measures. However, as reported 
in the survey, it has been challenging for countries to raise public awareness about larval source reduction in 
the domestic environment. Establishing a mechanism to increase citizens’ awareness and action is an 
important step forward. 
Larviciding is the primary method of response against WNV vectors (against mosquitoes in general, but that is 
outside the scope of this document). However, like any other method, it has limitations (e.g. patchy and non-
homogenous applications due to vast and/or inaccessible areas, such as domestic breeding sites, may have a 
significant impact on the overall efficacy of larviciding efforts). Achieving reductions in mosquito populations to 
levels below thresholds of WNV transmission solely by larviciding has been challenging and was shown not to 
be feasible in the nine studies identified in this report. 

  Other methods in addition to larviciding need to be applied in parallel, including adulticiding interventions, to 
reduce the risk of WNV. This is especially true when source reduction and larval control have failed or are not 
feasible. 

Aerial ULV adulticiding is the only method for which scientific evidence is currently available showing that it can 
reduce the incidence of WNV human cases and can be considered a useful method for WNV response strategies. 
However, its successful application depends on complex insecticide application technology and suitable weather 
conditions. Therefore, it should only be applied by well-trained professionals using spray guidance technologies 
and following appropriate application parameters to achieve treatment precision with minimal health and 
environmental impact. 

The implementation of vector control programmes is limited by a critical lack of evidence on the impact of vector 
control (primarily larviciding interventions) on preventing WNV outbreaks. Public health officials, veterinary 
authorities, academics and vector control operators in Europe and across the world should join forces in providing 
evidence from large-scale, controlled, operational trials on the efficacy of currently available vector control 
methods (singly and in combination under the umbrella of IVM) in reducing WNV circulation levels. Data on 
abundance reduction alone may be insufficient to shape public health policies. Due to the significant costs 
associated with the large scale of the studies required, it would make sense to identify areas with continuous WNV 
transmission and competent local surveillance and control infrastructure that could serve as research hubs. 

WNV vector control constraints were highlighted by EU Member States in relation to the limited availability of 
biocidal products; issues with biocide registration and regulatory frameworks on vector control applications, and 
limited availability of local expertise and resources. Furthermore, the majority of EU countries expressed the need 
for EU guidelines on WNV vector control. To address the above issues the following actions can be considered: 

 

 

 

A dialogue needs to be established between all relevant actors (public health authorities, European and 
national biocide authorities, the insecticide industry, vector control operators) to ensure that products are 
developed and registered that suit the requirements for an effective vector control strategy. The limited 
number of active substances available in the EU, in combination with the increasing reports of insecticide 
resistance, further emphasise the need to maintain a vector control toolbox containing a wide variety of 
chemical and non-chemical interventions. 
EU-wide technical guidelines for WNV vector management should be established, taking into account the 
currently available scientific evidence. It is important to set application standards for the various vector control 
methodologies to ensure effective and safe (both for humans and the environment) applications. Absence of 
knowledge and lack of technical expertise can lead to unsafe and ineffective treatments. Standardised training 
and certification of vector control professionals, if not already present, should be performed to further ensure 
effective and safe insecticide applications. 
There is a need to further strengthen and expand WNV vector surveillance and control capacities across the 
EU/EEA and in EU candidate/potential candidate countries, while investing in a centralised technical support 
mechanism to assist those countries that may not be able to locate resources and expertise for sufficient 
vector control response in the near future. 

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16.  Palmisano CT, Taylor V, Caillouet K, Byrd B, Wesson DM. Impact of West Nile virus outbreak upon St. 
Tammany Parish Mosquito Abatement District. J Am Mosq Control Assoc. 2005 Mar;21(1):33-8. 

17.  Carney RM, Husted S, Jean C, Glaser C, Kramer V. Efficacy of aerial spraying of mosquito adulticide in 
reducing incidence of West Nile Virus, California, 2005. Emerg Infect Dis. 2008 May;14(5):747-54. 

18.  Elnaiem DE, Kelley K, Wright S, Laffey R, Yoshimura G, Reed M, et al. Impact of aerial spraying of pyrethrin 
insecticide on Culex pipiens and Culex tarsalis (Diptera: Culicidae) abundance and West Nile virus infection 
rates in an urban/suburban area of Sacramento County, California. J Med Entomol. 2008 Jul;45(4):751-7. 

19.  Macedo P, Schleier J, Reed M, Kelley K, Goodman GW, Brown D. Aerial adulticiding in Sacramento County, 
California, 2007 – How was it different from 2005 and 2006? Proceedings and Papers of the SeventySixth 
Annual Conference of the Mosquito and Vector Control Association of California; 2008; Palm Springs, 
California. 

20.  Macedo PA, Schleier JJ, Reed M, Kelley K, Goodman GW, Brown DA, et al. Evaluation of efficacy and human 

health risk of aerial ultra-low volume applications of pyrethrins and piperonyl butoxide for adult mosquito 
management in response to West Nile virus activity in Sacramento County, California. J Am Mosq Control 
Assoc. 2010 Mar;26(1):57-66. 

36 

 
 
TECHNICAL REPORT 

 Vector control practice and strategies against West Nile virus 

21.  Lothrop HD, Lothrop BB, Gomsi DE, Reisen WK. Intensive early season adulticide applications decrease 

arbovirus transmission throughout the Coachella Valley, Riverside County, California. Vector Borne Zoonotic 
Dis. 2008 Aug;8(4):475-89. 

22.  Chaskopoulou A, Dovas CI, Chaintoutis SC, Kashefi J, Koehler P, Papanastassopoulou M. Detection and early 
warning of West Nile Virus circulation in Central Macedonia, Greece, using sentinel chickens and mosquitoes. 
Vector Borne Zoonotic Dis. 2013 Oct;13(10):723-32. 

23.  Ruktanonchai DJ, Stonecipher S, Lindsey N, McAllister J, Pillai SK, Horiuchi K, et al. Effect of aerial insecticide 
spraying on West Nile virus disease--north-central Texas, 2012. Am J Trop Med Hyg. 2014 Aug;91(2):240-5. 

24.  Chung WM, Buseman CM, Joyner SN, Hughes SM, Fomby TB, Luby JP, et al. The 2012 West Nile encephalitis 

epidemic in Dallas, Texas. JAMA. 2013 Jul 17;310(3):297-307. 

25.  Mutebi JP, Delorey MJ, Jones RC, Plate DK, Gerber SI, Gibbs KP, et al. The impact of adulticide applications 

on mosquito density in Chicago, 2005. J Am Mosq Control Assoc. 2011 Mar;27(1):69-76. 

26.  McMillan JR, Blakney RA, Mead DG, Coker SM, Morran LT, Waller LA, et al. Larviciding Culex spp. (Diptera: 
Culicidae) populations in catch basins and its impact on West Nile Virus transmission in urban parks in 
Atlanta, GA. J Med Entomol. 2019 Jan 8;56(1):222-32. 

27.  Nguyen C, Gray M, Burton TA, Foy SL, Foster JR, Gendernalik AL, et al. Evaluation of a novel West Nile virus 
transmission control strategy that targets Culex tarsalis with endectocide-containing blood meals. PLoS Negl 
Trop Dis. 2019 Mar;13(3):e0007210. 

28.  Sacramento Yolo Mosquito & Vector Control District. Mosquito and mosquito borne disease management plan 

Sacramento: Sacramento Yolo Mosquito & Vector Control District, 2005. Available from: 
https://www.fightthebite.net/download/Mosquito_Management_Plan.pdf 

29.  California Department of Health Services. California mosquito-borne virus surveillance and response plan. 
2005. Available from: http://westnile.ca.gov/website/publications/2005_ca_mosq_response_plan.pdf 

30.  Barber LM, Schleier JJ, Peterson RK. Economic cost analysis of West Nile virus outbreak, Sacramento County, 

California, USA, 2005. Emerg Infect Dis. 2010 Mar;16(3):480-6. 

31.  Chaskopoulou A, Latham MD, Pereira RM, Connelly R, Bonds JA, Koehler PG. Efficacy of aerial ultra-low 
volume applications of two novel water-based formulations of unsynergized pyrethroids against riceland 
mosquitoes in Greece. J Am Mosq Control Assoc. 2011 Dec;27(4):414-22. 

32.  Chaskopoulou A, Thrasyvoulou A, Goras G, Tananaki C, Latham MD, Kashefi J, et al. Nontarget effects of 

aerial mosquito adulticiding with water-based unsynergized pyrethroids on honey bees and other beneficial 
insects in an agricultural ecosystem of north Greece. J Med Entomol. 2014 May;51(3):720-4. 

33.  Petersen LR, Nasci RS, Beard CB, (eds). Emerging vector-borne diseases in the United States: What is next, 

and are we prepared? Forum on Microbial Threats; Board on Global Health; Health and Medicine Division; 
National Academies of Sciences, Engineering, and Medicine Global Health Impacts of Vector-Borne Diseases: 
2016; Washington (DC): National Academies Press (US)  

34.  Hamer GL, Donovan DJ, Hood-Nowotny R, Kaufman MG, Goldberg TL, Walker ED. Evaluation of a stable 

isotope method to mark naturally-breeding larval mosquitoes for adult dispersal studies. J Med Entomol. 2012 
Jan;49(1):61-70. 

37 

 
Annex 1.
Questionnaire survey about West Nile virus vector
mosquito surveillance and control activities

Fields marked with * are mandatory.

The main objective of this survey is to collate information on the vector control strategies against West Nile

virus (WNV) currently implemented for the prevention and response to WNV human outbreaks in EU

member countries, EU enlargement countries and EU neighbourhood policy countries.

The survey collects key information on:

Monitoring and surveillance of vectors of WNV

Control of vectors of WNV

Criteria for implementing methods

Monitoring and evaluation of methods

The survey results will feed into a technical report on the topic of control of West Nile virus vectors, which

will also be based on a literature review, expert knowledge and the discussion and report of an ECDC

expert meeting reviewing vector control practices and strategies against West Nile virus, and will be

prepared by a contractor for ECDC.

General Information about Respondent

Name (optional)

This information will be treated as strictly confidential.

Email (optional)

This information will be treated as strictly confidential.

Affiliation

*

*

Which country or region are you providing information for in this questionnaire?
Note: if you work in multiple sub-national regions, please fill in a separate questionnaire for each region.

In case of a sub-national region, please also provide the name of the country and the administrative level (e.g. NUTS2) of the region.

Do you give ECDC and its contractor your consent to use the answers you provide in the report?

*

Yes

No

If you want ECDC to send you a copy of the report when finished (expected mid 2020), please re-enter
your email address.

This information will be treated as strictly confidential.

WNV Risk Level

*

1. What risk level of West Nile virus applied to your country/region in 2019? Select the highest applicable
level.
See also: https://www.ecdc.europa.eu/sites/portal/files/media/en/publications/Publications/west-nile-virus-
risk-assessment-tool.pdf

0. No historical circulation of WNV and unsuitable ecological conditions (e.g. absence of vectors)

1. Ecological conditions suitable for WNV circulation but no historical circulation of WNV

2. Past evidence of WNV circulation

3a. Evidence of WNV circulation in mosquitoes or birds in the second part of the current season (August-

September-October)

3b. Evidence of WNV circulation in mosquitoes or birds in the first part of the current season (May-June-

July)

4. WNV-specific IgM detected in local non-vaccinated horse(s) or WNV detected in a local horse

5. Detection of at least one human case according to the EU case definition

Questions about Surveillance

2. WNV vector surveillance in your country/region is currently conducted at: (check all that apply)

National level

Regional level

Local level

None (not conducted, go to question 6)

Comments

Comments

3. WNV vector surveillance in your country/region is currently conducted by: (check all that apply)

Government

Academia

Private institutes

Other (please provide details under comments below)

Comments

4. WNV vector surveillance in your country/region is funded by: (check all that apply)

National government

Regional/local government

Academia

Privately

International funds

Other (please provide details under comments below)

Comments

5a. Please check all WNV surveillance activities that are performed in your country/region and give the

frequency

Weekly

Every

two

weeks

Monthly

Other

frequency

(please

specify in

comments

below)

Routine mosquito surveillance through standardized

methodologies and species identification (do not select if

mosquito surveillance is ad hoc or if species

identification is not performed)

WNV surveillance through mosquito screening for WNV

WNV surveillance through sentinel birds

WNV surveillance through sentinel equids

5b. Please check all other WNV surveillance activities that are performed in your country/region

WNV passive surveillance through sick/dead animals (birds, equids)

WNV passive surveillance through detection of human cases

WNV screening of human blood products

Pesticide resistance testing in mosquitoes

Other (please provide details under comments below)

Comments

Questions about Control

6. WNV vector control in your country/region is currently conducted by: (check all that apply)

*

Government

Academia

Private institutes

Other (please provide details under comments below)

None (not conducted, go to question 8b)

Comments

7. WNV vector control in your country/region is funded by: (check all that apply)

National government

Regional/local government

Academia

Privately

International funds

Other (please provide details under comments below)

Comments

8a. What specific WNV vector control methods were implemented in your country/region in 2019?

Adulticides: ULV (ultra low volume)– space spray (ground)

Adulticides: ULV– space spray (aerial)

Adulticides: LV (low volume) - surface spray (ground)

Larvicides: Chemical (e.g. insect growth regulators)

Larvicides: Biological (e.g. B.thuringensis var israelensis)

Larvicides: Water surface films

Larvicides: Physical source reduction

Community outreach & educational campaigns: Door-to-door

Community outreach & educational campaigns: Educational seminars

Community outreach & educational campaigns: Media

Other (specify in comments below)

Comments

8b. According to existing plans in your country/region, what specific WNV vector control methods (in rows)

are to be implemented in your country/region depending on the WNV risk level (in columns)? Check any

that apply to each (potential) risk level.

High

Vector

population

but no

historical

virus

detection

Evidence

of WNV

circulation

in the past

Evidence

of WNV

Evidence

of WNV

Evidence

Evidence

circulation

circulation

of WNV

of WNV

in

in

in one or

in one or

mosquitoes

mosquitoes

or birds in

Aug.–Oct.

or birds in

May–July

more

equids

more

humans

Adulticides:

ULV (ultra low

volume)–

space spray

(ground)

Adulticides:

ULV– space

spray (aerial)

Adulticides:

LV (low

volume) -

surface spray

(ground)

Larvicides:

Chemical (e.

g. insect

growth

regulators)

Larvicides:

Biological (e.

g. B.

thuringensis

var

israelensis)

Larvicides:

Water surface

films

Larvicides:

Physical

source

reduction

Community

outreach &

educational

campaigns:

Door-to-door

Community

outreach &

educational

campaigns:

Educational

seminars

Community

outreach &

educational

campaigns:

Media (e.g.

press, TV,

radio, social

media)

Other (specify

in comments

below)

None

I do not know

/ Not planned

for

Comments

9a. Which are in your opinion the most important constraints/limitations for implementing ULV (ultra low
volume) ground adulticiding
 for WNV vector control in your country/region? Rate the constraints from 1
to 5 stars with 5 stars being the strongest level of constraint, and 1 star being the weakest level. Leave
blank if you do not know.

High cost that limits frequency of application/method

High cost that limits the size of the area covered

Operational capacity constraints (knowledge, people, resources, equipment)

No or limited number of products registered for this use

Regulatory constraints that limit the application frequency of products/methods

Regulatory constraints that prevent areas from being treated

Unwillingness of community to collaborate

9b. Which are in your opinion the most important constraints/limitations for implementing ULV (ultra low
volume) aerial adulticiding
 for WNV vector control in your country/region? Rate the constraints from 1 to
5 stars with 5 stars being the strongest level of constraint, and 1 star being the weakest level. Leave blank
if you do not know.

High cost that limits frequency of application/method

High cost that limits the size of the area covered

Operational capacity constraints (knowledge, people, resources, equipment)

No or limited number of products registered for this use

Regulatory constraints that limit the application frequency of products/methods

Regulatory constraints that prevent areas from being treated

Unwillingness of community to collaborate

9c. Which are in your opinion the most important constraints/limitations for implementing LV (low volume)
adulticiding
 for WNV vector control in your country/region? Rate the constraints from 1 to 5 stars with 5
stars being the strongest level of constraint, and 1 star being the weakest level. Leave blank if you do not
know.

High cost that limits frequency of application/method

High cost that limits the size of the area covered

Operational capacity constraints (knowledge, people, resources, equipment)

No or limited number of products registered for this use

Unavailability of products with long residual efficacy

Regulatory constraints that limit the application frequency of products/methods

Regulatory constraints that prevent areas from being treated

Unwillingness of community to collaborate

9d. Which are in your opinion the most important constraints/limitations for implementing chemical
larviciding
stars being the strongest level of constraint, and 1 star being the weakest level. Leave blank if you do not
know.

 for WNV vector control in your country/region? Rate the constraints from 1 to 5 stars with 5

High cost that limits frequency of application/method

High cost that limits the size of the area covered

Operational capacity constraints (knowledge, people, resources, equipment)

No or limited number of products registered for this use

Unavailability of products with long residual efficacy

Regulatory constraints that limit the application frequency of products/methods

Regulatory constraints that prevent areas from being treated

Unwillingness of community to collaborate

9e. Which are in your opinion the most important constraints/limitations for implementing biological
larviciding
stars being the strongest level of constraint, and 1 star being the weakest level. Leave blank if you do not
know.

 for WNV vector control in your country/region? Rate the constraints from 1 to 5 stars with 5

High cost that limits frequency of application/method

High cost that limits the size of the area covered

Operational capacity constraints (knowledge, people, resources, equipment)

No or limited number of products registered for this use

Unavailability of products with long residual efficacy

Regulatory constraints that limit the application frequency of products/methods

Regulatory constraints that prevent areas from being treated

Unwillingness of community to collaborate

9f. Which are in your opinion the most important constraints/limitations for implementing larval source
reduction through environmental management
constraints from 1 to 5 stars with 5 stars being the strongest level of constraint, and 1 star being the
weakest level. Leave blank if you do not know.

 for WNV vector control in your country/region? Rate the

High cost that limits frequency of application/method

High cost that limits the size of the area covered

Operational capacity constraints (knowledge, people, resources, equipment)

Regulatory constraints that limit the application frequency of methods

Unwillingness of community to collaborate

9g. Which are in your opinion the most important constraints/limitations for implementing communication
campaigns
stars being the strongest level of constraint, and 1 star being the weakest level. Leave blank if you do not
know.

 for WNV vector control in your country/region? Rate the constraints from 1 to 5 stars with 5

High cost that limits frequency of application/method

High cost that limits the size of the area covered

Operational capacity constraints (knowledge, people, resources, equipment)

Unwillingness of community to collaborate

Comments

10. Are you aware of any method to control West Nile virus vector mosquitoes being/having been evaluated

/tested

 for 

outcomes

 and/or 

cost

 in your country/region in the last 5 years? Check all boxes that apply

according to the suggested aim.

For effect on

mosquito

abundance

For

Other objective

assessment

(describe in comments

of costs

below)

Aerial adulticide treatment

Ground adulticide treatment

Mass trapping

Personal protection (Communication

campaigns)

Environmental management

Chemical larvicides (e.g. Temephos,

Triflumuron)

Insect growth regulators larvicides (e.

g. Pyriproxyfen, Methoprene)

Non-biological non-chemical (e.g.

Aquatain®)

Biological larvicide (e.g. B.t.i.)

Other biological method (e.g. fishes,

copepods)

Door-to-door campaigns

Communication campaigns

Other (provide detail below)

Comments

Questions about Guidelines

*

11. In your opinion do you need new technical guidelines for WNV mosquito vector 
country/region?

surveillance

 in your

Yes

No

*

12. In your opinion do you need new technical guidelines for WNV mosquito vector 
/region?

control

 in your country

Yes

No

General

13. Please provide information on any additional 
surveillance and WNV vector control in your country/region

issues/challenges

 you are facing in relation to WNV

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