Towards a policy decision on Aedes
japonicus

Risk assessment of Aedes japonicus in the
Netherlands

RIVM Letter report 2018-0091
A. Stroo │ A. Ibañez-Justicia │ M. Braks

Towards a policy decision on Aedes
japonicus
Risk assessment of Aedes japonicus in the
Netherlands

RIVM Letter report 2018-0091
A. Stroo │ A. Ibañez-Justicia │ M. Braks

RIVM Letter report 2018-0091

Colophon

© RIVM 2018
Parts of this publication may be reproduced, provided acknowledgement
is given to the: National Institute for Public Health and the Environment,
and the title and year of publication are cited.
DOI 10.21945/RIVM-2018-0091

A. Stroo (author), NVWA
A. Ibañez-Justicia (author), NVWA
M. Braks (author), RIVM
Contact:
Marieta Braks
Centre for Zoonoses and Environmental Microbiology, National Institute
for Public Health and Environment (RIVM)
marieta.braks@rivm.nl
Centre for Monitoring of Vectors, Netherlands Food and Consumer
Product Safety Authority (NVWA), National Reference Centre (NRC),
Ministry of Economic Affairs, Wageningen, The Netherlands.
This investigation was performed for the account of the Ministry of
Health, Welfare and Sport, within the framework of policy advice to the
Public Health department.

This is a publication of the:
National Institute for Public Health
and the Environment
P.O. Box 1 | 3720 BA Bilthoven
The Netherlands
www.rivm.nl/en
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RIVM Letter report 2018-0091

Synopsis

Towards a policy decision on Aedes japonicus
Risk assessment of Aedes japonicus in the Netherlands
The Dutch government wants to limit the risk for local transmission of
mosquito-borne diseases and therefore aims to limit the establishment
of invasive exotic mosquitoes in the Netherlands. At the request of the
Ministry of Public Health, RIVM and CMV have investigated which
approach is appropriate for the Asian bush mosquito, Aedes japonicus.
An effective approach requires a tailor-made method and requires
choices. Which choices are made depends on the chance of transmission
of diseases by a specific mosquito species, the effect of the control and
the costs thereof. In the Netherlands, mosquitoes do not form a major
problem as vectors of human diseases at the moment. To become
problematic, two preconditions are required. There must be human
biting mosquitoes that are able to transmit pathogens, and there must
be pathogens that can be transmitted by mosquitoes. In the Netherlands
such pathogens are rare. In addition, in the Netherlands mosquitoes are
not well able to transmit pathogens. The establishment of specific exotic
mosquitoes could increase the risk of transmission of pathogens in the
Netherlands.
The Asian bush mosquito was discovered in the Netherlands in 2012 and
was found present in large parts of Lelystad. In recent years, the area,
where this species is present, has expanded. This makes it increasingly
difficult to fight the mosquito and the costs for the control increase. On
the other hand, the risk of transmission of pathogens by Asian bush
mosquito is small. This mosquito does not play an important role in
outbreaks of mosquito-borne diseases. Only under specific conditions in
the laboratory and field can Asian bush mosquito transmit pathogens.
Worldwide only a few patients are known who may have become ill
through this mosquito. The risk of the Asian bush mosquito in the
Netherlands is comparable to that of a number of native mosquito
species. The Asian bush mosquito provides a small added risk of
spreading diseases in the Netherlands.
Keywords: risk assessment, Asian bush mosquito, Aedes japonicus,
Netherlands,

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Publiekssamenvatting

Op weg naar een beleidsbeslissing over de Aziatische bosmug:
Risicobeoordeling van de Aziatische bosmug in Nederland
De overheid wil de kans op ziekten, die door muggen overgedragen
worden, beperken en daarom de vestiging van invasieve exotische
muggen in Nederland beperken. Het RIVM en het CMV hebben op
verzoek van VWS onderzocht welke aanpak gekozen kan worden voor
de Aziatische bosmug Aedes japonicus.
Een effectieve aanpak vergt maatwerk en vraagt om keuzes. Een goede
aanpak hangt af van de kans op overdracht van ziekten door een
specifieke muggensoort, het effect van de bestrijding en de kosten
daarvan. In Nederland zijn muggen als overbrenger van ziekten op dit
moment geen groot probleem. Voordat muggen op grote schaal ziekten
kunnen verspreiden zijn er twee randvoorwaarden nodig. Er moeten
muggen (die van nature ook vaak mensen bijten) aanwezig zijn die
ziekten kunnen overbrengen, en er moeten ziekteverwekkers aanwezig
zijn die door muggen overgebracht kunnen worden. In Nederland komen
zulke ziekteverwekkers niet of nauwelijks voor. Bovendien komen in
Nederland vooral muggen voor die niet goed in staat zijn om ziekten
over te dragen. De vestiging van specifieke exotische muggen zou het
risico op overdracht van ziekten in Nederland kunnen vergroten.
De Aziatische bosmug is in 2012 aangetroffen in Nederland en bleek al
in grote delen van Lelystad voor te komen. In de afgelopen jaren is het
leefgebied van deze soort uitgebreid. Daarmee wordt het moeilijker om
de mug te bestrijden en stijgen de kosten voor de bestrijding.
Daartegenover staat dat het risico van overdracht van ziekten door de
Aziatische bosmug klein is. Deze mug speelt geen belangrijke rol bij
uitbraken van door muggen overdraagbare zieken. Alleen onder
specifieke omstandigheden in het laboratorium en veld kan Aziatische
bosmug ziekteverwekkers overbrengen. Wereldwijd zijn slechts enkele
patiënten bekend die mogelijk via deze mug ziek zijn geworden. Het
risico van de Aziatische bosmug in Nederland is vergelijkbaar met dat
van een aantal inheemse muggensoorten. De Aziatische bosmug zorgt
voor een klein toegevoegd risico op verspreiding van ziekten in
Nederland.
Kernwoorden: risicobeoordeling, Aziatische bosmug, Aedes japonicus,
Nederland,

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Contents

Summary — 9
1

Background — 11

2
2.1
2.2
2.3

Risk assessment — 13
Invasion status of Aedes japonicus in the Netherlands — 13
Vector status of Aedes japonicus worldwide — 14
Risk status of Aedes japonicus in the Netherlands — 15

3

Conclusion — 21

4
4.1
4.2

4.4

Appendices: Literature search — 23
Appendix 1: Search strings for literature search — 23
Appendix 2: Vector potential of Aedes. japonicus for various mosquito
borne pathogens — 24
Appendix 3: Anthropophily from blood meal analyses of
Aedes japonicus — 29
Appendix 4: Hosts for Aedes japonicus — 29

5

References — 31

4.3

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Summary

New establishments of invasive mosquito species can increase the
transmission risk of mosquito-borne diseases. Depending on the risk
posed by a particular invasive species and the stage of the invasion,
management scenarios may change and differ between invasive species.
The Aedes japonicus population recently expanded beyond the city limits
of Lelystad and entered a new stage of invasion. To support the policy
decision making process about the proportionality of future strategies in
regard to the control of Ae. japonicus, an assessment of the risks of
mosquito species for the transmission of pathogens important for public
health was requested by the ministry of Health, Welfare and Sport.
A broad establishment of Ae. japonicus in the Netherlands would pose a
previously non-existing, but low risk for transmission of six pathogens,
since Ae. japonicus is the only potential vector present. It may also
introduce an additional, but also low risk of transmission of five
pathogens currently posed by native mosquito species. Despite the fact
that Ae. japonicus has been shown to have biological potential for
spreading eleven mosquito-borne pathogens, the actual risk for
transmission of these pathogens in day to day practice in the
Netherlands is considered (very) low.

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1

Background

New establishments of invasive mosquito species can increase the
transmission risk of mosquito-borne diseases. It is Dutch policy to
counter this with a set of interventions. The management options
depend on the stage of the invasion. As rule of thumb, as the invasion
progresses, the effectiveness of interventions decreases while their cost
increases (Figure 1).

Figure 1: Invasion processes and management options (source
https://invasives.org.au/strategy-invasive-species-australia/)

Different scenarios with respect to management options towards
invasive mosquito species in the Netherlands are presented in Figure 2.
Depending on the stage of the invasion and the risk posed by a
particular invasive species, management scenarios may change and
differ between invasive species.
In the Netherlands, current policy on invasive mosquitoes is to prevent
establishment of introduced invasive species, and in the event that
(local) establishment preceded detection, to control, contain and prevent
further introduction. For the Asian bush mosquito Aedes japonicus (in
Dutch known as “Aziatische bosmug”) this entails to eradicate new
introductions and to control and contain the local established population
in Lelystad. After Ae. japonicus was found in 2017 to have spread from
Lelystad to Zeewolde, having several breeding habitats in-between, the
question arose to what extent the various management options towards
this invasive mosquito species are proportional to the risks it poses. The
current policy towards Ae. japonicus is depicted as Scenario 1 (Figure
2).
To support the policy decision making process about the proportionality
of future strategies in regard to Ae. japonicus, an assessment of the
risks of mosquito species for the transmission pathogens important for

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the public health was requested by the ministry of Health, Welfare and
Sport.
The risk assessment of Ae. japonicus will be build up in the following
three sections:
1. Invasion status in the Netherlands
2. Vector status worldwide
3. Risk status for public health in the Netherlands
The risk assessment will, together with the supporting data, provide a
solid basis for policy decision on the management of Ae. japonicus. The
decision making itself and its result do not form part of this document.
Specific risks for veterinary health are not taken into consideration.
The document has been written by Arjan Stroo and Adolfo IbañezJusticia, CMV and Marieta Braks (PhD), RIVM. Valuable input has been
provided by Sander Koenraadt, Associate professor at the Laboratory of
Entomology (WUR) and Chantal Reusken, Assistant Professor Public
Health Virology, Preparedness and Response (Erasmus MC).

Figure 2: Different scenarios with respect to management options.

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2

Risk assessment

2.1

Invasion status of Aedes japonicus in the Netherlands
In 2012, the Asian bush mosquito (Aedes japonicus japonicus
(Theobald)) was detected for the first time in the Netherlands, in the
municipality of Lelystad. Aedes japonicus (also known under its formally
correct name as Hulecoeteomyia japonica, or under another synonym as
Ochlerotatus japonicus) is an invasive mosquito species that originates
from Japan, Korea, and Southern China (Tanaka et al. 1979) and has
also been found in south-eastern Russia (Gutsevich and Dubitskyi
1987). The first interception of the species in Europe occurred in France
in the year 2000 (Schaffner et al. 2003). Afterwards, established
populations of this species have been found in Belgium (Versteirt et al.
2009), Switzerland (Schaffner et al. 2009), Germany (Becker et al.
2011, Kampen et al. 2012, Werner and Kampen 2013), Austria, and
Slovenia (Seidel et al. 2012). Since the first interceptions in the 1990s,
Ae. japonicus has also successfully colonized numerous states of the
United States, and by 2000, it was already reported from south-eastern
Canada (Kampen and Werner 2014).
After the initial catch in 2012 in the city of Lelystad, subsequent
research revealed hundreds of specimens, mostly found in the periurban areas of the city in 2013 (Ibañez-Justicia et al. 2014). Allotment
gardens turned out to be important reproductive areas (Ibañez-Justicia
et al. 2018).
Initially, the National Coordination Centre for Communicable Disease
Control, informed by CMV about the situation, advised the Ministry of
Public Health not to engage in active control of the population, since at
the time no human disease cases vectored by Ae. japonicus were
known. Active control was only started after novel information on the
possible role of Ae. japonicus in the transmission of La Crosse virus in
the USA. Given the fact that the species was limited to the municipality
of Lelystad, a targeted mosquito control campaign was initiated in 2015
with the objective of reducing populations in locations with the highest
concentrations of Ae. japonicus breeding sites (allotment gardens).
Mosquito control consisted of source reduction combined with application
of the larvicide Vectomax® in breeding sites. Source reduction, also
known as physical control, is one part of Integrated Pest Management
(IPM) and is accomplished by eliminating mosquito breeding sites,
preferably permanently. This can be as simple as discarding containers
which hold water capable of producing mosquitoes. Source reduction is
usually considered the most effective and economical of the mosquito
control techniques.
At all eight allotment garden locations, mosquito control effectiveness
has been systematically measured by sampling larvae from breeding
sites. Six measurements were performed in 2015 and 2016. Results
showed that the effectiveness of the mosquito control actions was
similar in all treated allotment gardens and resulted in a significant
reduction (around 80 %) in Ae. japonicus larval abundance. Rain barrels
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RIVM Letter report 2018-0091

at the allotments represent the most frequent breeding site in Lelystad,
but every water filled artificial container is a potential breeding site for
the species. The species has never been found in surface water and
naturally occurring container-like breeding sites like tree holes were
never found occupied. Until September 2017, Ae. japonicus was not
found in samples from a surveillance that assessed potential expansion
of the distribution into other towns besides Lelystad in the province of
Flevoland.
In the fall of 2017, however, Ae japonicus was found in an allotment in
Zeewolde (NVWA 2018), a municipality approximately 19 km south of
the positive allotment gardens of Lelystad. In a subsequent surveillance
of 27 locations (farms) in a transect between Lelystad and Zeewolde,
four were positive for Ae. japonicus (Figure 3).

Figure 3: Findings of Ae. japonicus in the province of Flevoland, since its first
detection in 2012.

Since the discovery of Ae. japonicus in Lelystad, not a single complaint
about biting nuisance was received by the NVWA, notwithstanding the
fact that the hotspot are intensively used allotment gardens where
people are also around at times when it will bite (at dusk).
2.2

Vector status of Aedes japonicus worldwide
The vector status of Ae. japonicus is determined by the current
knowledge of its ability to transmit pathogens either under laboratory
conditions (vector competence) or in field situations (vector capacity).
Its most recent has been assessed in a literature review performed in
January 2018 using the literature database PubMed
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RIVM Letter report 2018-0091

(https://www.ncbi.nlm.nih.gov/pubmed/). In the following section, we
summarize the information on the vector status of Ae. japonicus as well
as its feeding behaviour and nuisance. Detailed report of the literature
search can be found in the Appendices 1-4.
Of the 153 papers found, a total of 30 unique papers contained
information related to the vector status of Ae. japonicus. In the
laboratory, vector competence has been shown for CHIKV and DENV and
the following wildlife-borne zoonotic pathogens CCV, EEEV, JEV, LACV,
SLEV, WNV, GETV, and Dirofilaria immitis / repens. Among the wildlife
zoonotic pathogens, Ae. japonicus has been found infected in the field
with CVV, WNV and LACV, but was only shown to play a role in the
transmission cycle of the latter (Appendix 2).
Table 1: Pathogens for which Ae. japonicus has shown vector competence
and/or vector capacity.

Pathogen

Viruses, abbreviation
Cache Valley virus, CVV
Chikungunya virus, CHIKV
Dengue virus, DENV
Eastern equine encephalitis virus,
EEEV
Getah virus, GETV
Japanese encephalitis virus, JEV
La Crosse encephalitis virus, LACV
Rift Valley virus, RVF
Saint Louis encephalitis virus, SLEV
West Nile virus, WNV
Parasite, abbreviation
Dirofilaria immitis/ repens, Diro

Vector
competence

Vector
capacity

√
√
√
√
√
√
√
√
√
√

√

√

Aedes japonicus displays a rather opportunistic feeding behaviour and
has been found feeding on mammals, including humans and bird species
(Appendix 3). Although based on a small number of field studies, a high
variation in the percentages of human blood in the available blood meal
analysis also indicates a rather opportunistic feeding behaviour
(Appendix 4).
Aedes japonicus colonises urbanised and suburban environments
(Schaffner et al. 2009) and females are active during the late afternoon
and evening (Turell et al. 2005). Reports from Switzerland mention
moderate to severe nuisance (Seidel et al. 2016).
2.3

Risk status of Aedes japonicus in the Netherlands
New establishments of invasive mosquito species can increase the risk
of transmission of mosquito borne pathogens currently posed by native
mosquito species. There is no current Dutch policy for the control or
management of native mosquitoes, irrespective of whether they are
potential vectors. An assessment as to what extent the risk will increase
by a well-established Ae. japonicus population in the future is an

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important aspect in the policy decision making process about the
proportionality of future (control) strategies in regard to Ae. japonicus.
In 2016, the vector status of 26 native mosquito species in the
Netherlands (Ibañez-Justicia et al. 2015) was reviewed and summarized
(Braks and Stroo 2016), using the following coding system for vector
potential developed by ECDC (ECDC 2014):
Empty cell = Absence of information for the species
0 = Refractory to infection in the laboratory
1 = Species infected in nature only
2 = Species competent in the laboratory only (at low, moderate
or high level)
3 = Species infected in nature and competent (fulfilling 1 and 2)
4 = Species known as vectors in regions and countries outside Europe
only
5 = Species known as vectors in Europe
For 14 of these 26 native mosquito species, evidence for some level of
vector potential exists (Braks and Stroo 2016). It is important to realise
that no information on vector potential of the 12 remaining species is
available in the literature, because they either have never been tested
or are never found infected. The information on the vector status of Ae.
japonicus reported in paragraph 2.2. is transferred into vector potential
codes using the same coding system.
In Table 2, the vector potential of 26 native mosquitoes with respect to
11 pathogens (Braks and Stroo 2016) is combined with that of Ae.
japonicus with respect to 12 pathogens. With the addition of the recent
publication on Zika virus detection in field collected Ae. vexans
(Elizondo-Quiroga et al. 2018), the table contains the vector potential of
27 species for 16 pathogens. A more visual representation of the added
risk of Ae. japonicus is shown in Figure 4.
Four of the 16 pathogens shown in Table 2, CHIKV, DENV, ZIKV and
Plasm circulate strictly between humans via mosquitoes. The pathogen
can be introduced by travellers with viremia or parasitemia. The
remainder include zoonotic pathogens for which humans play no or a
subordinate role in the transmission ecology. For the majority of these
zoonotic pathogens, amplification in an enzootic wild cycle precedes
transmission to humans.

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Table 2: Vector potential of Ae. japonicus and 26 native mosquito species to
various pathogens (adapted from (ECDC 2014, Braks and Stroo 2016))

Other
pathogens*
CHIKV
DENV
GETV
LACV
SINV
USUTV
ZIKV
F.tula
CVV
EEEV
JEV
RVFV
SLEV
WNV
Diro
Plasm
2
2
1
2
2
2
2
4
2
2
3
Viral pathogens

Mosquito species
Ae. japonicus
Ae. annulipes/cantans
Ae. caspius
Ae. cinereus
Ae. communis
Ae. detritus
Ae. dorsalis
Ae. flavescens
Ae. geniculatus
Ae. leucomelas
Ae. nigrinus
Ae. punctor
Ae. riparius
Ae. rusticus
Ae. sticticus
Ae. vexans
An. claviger
An. maculipennis s.l.
An. plumbeus
Cq. richiardii
Cx. modestus
Cx. pipiens/torrentium
Cx. territans
Cs. annulata
Cs. fumipennis
Cs. morsitans
Cs. subochrea

4

1

1

2

5
5

5

1
1
1

3

4

3

4

1
2
1
5
5

3
5
5

1

3

1

5

~ abbreviation of pathogens see table 1 and appendix 2, *F. tula refers to Fransicella
tularensis, Plasm refers to malaria parasites

For 11 pathogens, vector potential of Ae. japonicus has been shown. A
broad establishment of this invasive mosquito species in the Netherlands
would pose a previously non-existing risk for transmission of six
pathogens (CHIK, CVV, DENV, JEV, LACV, SLEV), since Ae. japonicus is
the only potential vector present. In addition it would introduce an
additional risk of transmission of five pathogens (EEEV, GETV, RFV, WNV
and Diro) currently posed by native mosquito species.
The vector potential of Ae. japonicus for 10 of the 11 pathogens is low,
1 or 2. For the latter, it means that proof of the ability to transmit these
pathogens is only available from laboratory studies (Figure 4).
Extrapolation of laboratory results to field situations is difficult.
Laboratory studies examine the vector competence under artificial,
controlled, often tropical, conditions, often outside the natural range of
condition in the Netherlands. This adds to the uncertainty of a possible
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5

1

3
1
3

4
3
3

RIVM Letter report 2018-0091

role in transmission in more temperate areas. Knowledge of the context
and limitations of the laboratory experiments is essential when
interpreting the results. Unfortunately, conclusions are often drawn
outside the validity range of the assumptions. The validity of laboratory
data in the outside world is questionable as responses to varying
conditions or key parameters can be missed. On the other hand, while
the absence of autochthonous cases of for example of dengue in areas
where Ae. japonicus is abundant, might suggest that Ae. japonicus
might not be considered a good vector, this observation does not
provide conclusive evidence as non-entomological factors determining
the vector capacity (a.o. density of susceptible hosts, temperature)
might be missing.
Due to the recent large scale invasions of Ae. japonicus in USA and
Europe, the number of investigations into its vector competence is
increasing, while investigations into various non-invasive Aedes species
are lacking. Haphazard comparisons of Ae. japonicus with invasive
important vector species, such Ae. aegypti and Ae. albopictus, that
belong to another subgenus, may lead to erroneous conclusions.
Only for La Crosse encephalitis virus, Ae. japonicus appears to interact
in the natural transmission cycle, which is predominantly driven by the
American tree hole mosquito Aedes triseriatus. Upon invasion and
establishment into the LACV endemic area, Ae. japonicus appeared to
act as one of the bridge vectors from the wildlife reservoirs for LACV to
humans. For LACV to arrive to Europe is highly unlikely, given that
chipmunks and squirrel species, that are the dominant hosts in the
sylvatic cycle in the endemic area in the United States, are not present
in nature in the Netherlands and are not even allowed as pets here.
Other squirrel species, but within the same genus, do occur, as does the
susceptible red fox, but at much lower densities than the reservoir
species in the US. Chances of introduction, establishment and spread in
a sylvatic transmission cycle are therefore considered extremely small
for this virus. An important lesson from the LACV epidemiology in the US
might be that upon establishment of one of the above mentioned
zoonotic pathogens in the Netherlands, the host preferences of Ae.
japonicus may ease bridging with humans.
After LACV, WNV represents the next highest added score from Ae.
japonicus. However, in contrast with LACV, other (potential) native
vectors for WNV are already present in the Netherlands.

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Figure 4: Risk potential. Added risk potential from Ae. japonicus upon
establishment (solid circles) to the risk potential from individual native mosquito
species (open circles) in the Netherlands . Circles in green area indicate at
mosquito species with evidence for vector competence; circles in pink area
indicate at mosquito species with evidence for vector capacity.

In the Netherlands, Ae. japonicus will most probably flourish in periurban and rural areas, being dependent on man-made breeding places
and favouring relatively natural resting places. Basically nothing is
known about its feeding behaviour in Lelystad, except for anecdotal
information indicating that some human biting occurs in and along forest
edges and in the evening. The relative low nuisance level in Lelystad
compared to other European locations remains unexplained. A missmatch between the vector activity and human activity in the heavy
infested locations in Lelystad, namely the allotment gardens is not likely,
many people are present during the biting hours.

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3

Conclusion

•
•

Ae. japonicus has been shown to have vector potential for 11
mosquito-borne pathogens
A broad establishment of Ae. japonicus in the Netherlands would
o Pose a previously non-existing, but low risk for transmission
of six pathogens (CHIK, CVV, DENV, JEV, LACV, SLEV), since
Ae. japonicus is the only potential vector present.
o Introduce an additional, but low risk of transmission of five
pathogens (EEEV, GETV, RFV, WNV and Diro) currently posed
by native mosquito species.

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4

Appendices: Literature search

4.1

Appendix 1: Search strings for literature search

Keyword

Total
number
of
records
153

Number
of
records
used
24

Ochlerotatus
japonicus

51

12

Hulecoeteomyia
japonica

6

3

Aedes
japonicus

References

(Takashima and Hashimoto 1985, Sucharit et al.
1989, Takashima and Rosen 1989, Sardelis and
Turell 2001, Turell et al. 2001b, Turell et al. 2001a,
Sardelis et al. 2002b, Medlock et al. 2005, Styer et
al. 2007, Molaei et al. 2009, Leisnham and Juliano
2012, Schaffner et al. 2013, Turell et al. 2013,
Andreadis et al. 2014, Huber et al. 2014, Krebs et
al. 2014, Harris et al. 2015, Westby et al. 2015,
Bara et al. 2016, Muturi et al. 2016, Schonenberger
et al. 2016, Silaghi et al. 2017, Urquhart et al.
2017, Wagner et al. 2018)
(Sardelis and Turell 2001, Turell et al. 2001a,
Sardelis et al. 2002b, Sardelis et al. 2002a,
Andreadis et al. 2003, Sardelis et al. 2003, Medlock
et al. 2005, Andreadis and Wolfe 2010, Andreadis et
al. 2014, Huber et al. 2014, Bara and Muturi 2015,
Bara et al. 2016)
(Huber et al. 2014, Schonenberger et al. 2016,
Wagner et al. 2018)

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4.2

Appendix 2: Vector potential of Aedes japonicus for various mosquito-borne pathogens

Pathogen
Abbreviation
Cache Valley
Virus
CVV

Ref.

Chikungunya
virus
CHIKV

(Schaffner
et al. 2011)

Oral feeding through a
chicken skin,
incubated 14 days.
The dissemination rate
was lower than for
CHIKV (2/15; 13.3%).

One CVV infected Ae. japonicus (1 pool out of 3120). If proven to be
a competent vector, Oc. japonicus could contribute to local
transmission as regional studies have shown that females feed
exclusively on mammalian hosts that include mostly white-tailed deer
and humans
Ae. japonicus has a vector potential for both DENV and CHIKV.
Considering the high abundance of the species in urban environments
and its ability to feed on human, these results plead to include this
species when processing risk assessments for mosquito-borne
diseases. The vector competence study shows low dissemination rate
for CHIKV.

Dengue virus
DENV

(Schaffner
et al. 2011)

Oral feeding through a
chicken skin IP 14
days.
The dissemination rate
was high for DENV
(10/11; 91.0%)

Ae. japonicus has a vector potential for both DENV and CHIKV.
Considering the high abundance of the species in urban environments
and its ability to feed on human, these results plead to include this
species when processing risk assessments for mosquito-borne
diseases. The vector competence study shows high dissemination rate
for DENV.

Dirofilaria
immitis/
Dirofilaria
repens
Diro

(Silaghi et
al. 2017)

Eastern
equine

(Sardelis et
al. 2002b)

Anticoagulated
microfilariaemic blood
was fed at a density of
3000 mf/ml to
mosquitoes with a
hemotek system
Chickens were
inoculated

In field-collected Ae. japonicus infectious L3 larvae of both D. immitis
and D. repens developed, rendering this mosquito species an efficient
vector for both filarial species, and indicating that this invasive and
locally highly abundant species may contribute to a transmission of
filarial worms. our findings suggest that there is an increased risk of
Dirofilaria transmission in areas populated by this species
Although not a highly efficient vector under laboratory conditions (1525% transmission rate), Oc. j. japonicus can become infected with

(Andreadis
et al. 2014)

Page 24 of 34

Information
provided
Isolation virus from
field populations

Author results / risk perception

Disease
occurrence
Enzootic
throughout
Americas
(Andreadis et
al. 2014)
Endemic in
Africa and
Asia; Freq.
imported into
Europe
(Schaffner et
al. 2013)
Epid in
Americas
Endemic in
Africa,
Americas,
Asia; Freq.
imported into
Europe
(Schaffner et
al. 2013)
Endemic in
southern
Europe and
the Americas
(Schaffner et
al. 2013)
Americas; No
evidence of

Vector
potential
1

2

2

2

2

RIVM Letter report 2018-0091

Pathogen
Abbreviation
encephalitis
virus
EEEV

Ref.

Getah virus
GETV

(Takashima
and
Hashimoto
1985)

Several species of
mosquitoes, were
examined for infection
rates following 21
days’ incubation at
28°C
after ingesting of
virus-blood mixture

Japanese
encephalitis
virus
JEV

(Takashima
and Rosen
1989)

Wild caught adult
mosquitoes.
Mosquitoes
were fed upon a virusblood mixture soaked
on cotton or were fed
upon a viremic chick
that was inoculated
with virus.
Oral feeding, human
blood, cotton stick
soaked. only 8 % of
females accepted the

(Huber et
al. 2014)

Information
provided
subcutaneously and
mosquitoes were
allowed to feed on
them 24 h later.
IP 14 days.

Author results / risk perception
EEE virus and transmit it by bite. The results of this study combined
with the limited knowledge of the distribution and bionomics of this
species in the United States suggest that Oc. j. japonicus could
function as a bridge vector for EEE virus between the enzootic avian
cycle and susceptible mammalian hosts. Ae. japonicus is not a highly
efficient vector under laboratory conditions.
44 to 50% of Ae. japonicus were infected

Ae. japonicus had vector competence for Japanese encephalitis virus
and the capability to transmit the virus vertically to its offspring. This
mosquito species was able to transmit the virus to suckling mice after
feeding on a virus-blood mixture as well as on a viremic chick. Vertical
transmission of the virus was demonstrated in Ae. japonicus after
intrathoracic inoculation; the highest
minimum infection rate was 0.7%.
All females challenged with JEV were positive for JEV-RNA (100 %
infection rate) on day 14 post-infection.

Page 25 of 34

Disease
occurrence
introduction
into Europe to
date
(Schaffner et
al. 2013)

Vector
potential

At present,
GETV has
spread across
Eurasia and
Southeast
Asia, including
mainland
China, Korea,
Japan,
Mongolia, and
Russia (Li et
al. 2017)
Endemic in
Asia; No clear
evidence of
introduction
into Europe to
date
(Schaffner et
al. 2013)

2

2

RIVM Letter report 2018-0091

Pathogen
Abbreviation

Ref.

Information
provided
artificial blood meal.
After Oc. j. japonicus
ingested virus from
hamsters with viremia,
its estimated
transmission rates
were 35-88%

Author results / risk perception

Disease
occurrence

Vector
potential

La Crosse
virus
LACV

(Sardelis et
al. 2002a)

Virus had disseminated from the midgut in 100% (8/8) of these
specimens. Oc. j. japonicus could function as an additional vector of
LAC virus.

4

(Westby et
al. 2015)

Field collected adults
tested for LCV

(Bara et al.
2016)

Field collected pupae
delivered adults in the
lab, which were fed via
the Hemotek with
LACV infected bovine
blood

(Harris et
al. 2015)

Field infected

The single positive Ae. japonicus pool was collected in May. The future
role of Ae. japonicus in the maintenance or
transmission of LACV in this, and other endemic regions, is unknown,
but it is an aggressive invader and has become established in many
parts of the country where LACV is known to occur. In some areas of
the USA, Ae. japonicus is
replacing the native species.
Oc. japonicus had the highest Effective Vector Competence value
(2.92), followed by Ae. albopictus (EVC=1.55), Ae. aegypti
(EVC=0.88), and Oc. triseriatus (EVC=0.64).
while LACV-positive field collections of Oc. japonicus have been
reported in Tennessee, Virginia, and West Virginia (Gerhardt et al.
2001, Lambert et al. 2010, Westby et al. 2011, Harris et al. 2015).
For both species, LACV-positive samples were obtained from mosquito
eggs or larvae, indicating active vertical transmission. This study
conclusively demonstrates that Oc. japonicus and Ae. albopictus
develop disseminated infections within an epidemiologically relevant
timeframe that should allow them to be efficient vectors of LACV.
The authors report 2 independent isolations of LACV from adult Ae.
japonicus mosquitoes in southwestern Virginia and 7 field detections
of LACV RNA from adults (Virginia and West Virginia) and adults

Endemic in
northern
America; No
evidence of
introduction
into Europe to
date
(Schaffner et
al. 2013)

Page 26 of 34

RIVM Letter report 2018-0091

Pathogen
Abbreviation

Ref.

Rift valley
virus
RVF

(Turell et
al. 2013)

St. Louis
encephalitis
virus
SLEV

(Sardelis et
al. 2003)

West Nile
virus
WNV

(Turell et
al. 2001b)
(CDC 2000)

Information
provided
Fed on infected adult
hamsters, infection
rates >90% and
dissemination rates
>84%
after feeding on
chickens with viremias

Fed on chickens
infected with WN virus
(from 1999 outbreak).
IP 14 d.
Field infected

(Styer et
al. 2007)
(Huber et
al. 2014)

Oral feeding, human
blood, cotton stick
soaked. only 8 % of
Ae. j. japonicus

Author results / risk perception
reared from eggs (Virginia). Suggesting that Ae. japonicus mosquitoes
may play a major role in transmission of LACV to humans.
Ae. japonicus proved to be highly efficient laboratory vectors of RVFV.
Ae. j. japonicus should be targeted for immediate control should RVFV
be introduced into an area where this mosquito is now present
Infection rates in Oc. j. japonicus were 0-33%, Estimated
transmission rates at viral doses sufficient to infect the tested species
were 29-84%. Because of its continued geographic expansion, field
and laboratory evidence incriminating it as a vector of the closely
related West Nile virus, and its ability to transmit SLE in the
laboratory, Oc. j. japonicus should be considered as a potential
enzootic or epizootic vector of SLE.
Aedes japonicus (Theobald) were highly susceptible to infection, and
nearly all individuals with a disseminated infection transmitted virus
by bite.
However, the recent isolation of WNvirus from three pools of Ae.
japonicus collected in New York (CDC 2000b) indicates that this
species may be involved in nature.
The amount of WNV inoculated by Ae. japonicus 1during feeding were
not significantly different from those inoculated by Cx. tarsalis, Cx.
pipiens, and Ae. triseriatus.
Of 67 Ae. j. japonicus females challenged by feeding of WNVcontaining blood, none had measurable amounts of WNV-RNA (0 %
infection rate) on day 14 post-infection.
The authors suggest that differences in genetic background between

Page 27 of 34

Disease
occurrence

Vector
potential

Africa,
Arabian
peninsula
(Turell et al.
2013)
Endemic in
the Americas;
Not seen in
Europe to
date
(Schaffner et
al. 2013)
Worldwide
(Schaffner et
al. 2013)

2

2

3

RIVM Letter report 2018-0091

Pathogen
Abbreviation

Ref.

(Wagner et
al. 2018)

Page 28 of 34

Information
provided
females accepted the
artificial blood meal.
Wild caught adults,
hemotek with chicken
skin.

Author results / risk perception
Ae. j. japonicus populations from North America and Germany are
most likely responsible for the differences in vector competence for
WNV. Author suggest, possible contribution as enzootic vector.
This study confirms that Ae. japonicus is highly susceptible to
infections with WNV, seemingly even more so than Cx. pipiens, as has
been shown in previous studies from the U.S.A. (Turell et al., 2001).
This study shows that a field population of Ae. japonicus collected in
northeastern Switzerland is susceptible to two WNV strains under
Central European summer conditions. Given its high local abundances
and its opportunistic feeding behavior, including both mammals and
birds as hosts, Ae. japonicus is a potential key bridge vector of WNV in
Europe. Thus far, WNV has not occurred in areas that are inhabited by
this mosquito species.

Disease
occurrence

Vector
potential

RIVM Letter report 2018-0091

4.3

4.4

Appendix 3: Anthropophily from blood meal analyses of Aedes japonicus
Area

Area type

New Jersey
Belgium
Switzerland
New York state

suburban/nature
rural
zoo
nature

Percentage
human
blood
36%
60%
3%
0%

Reference
(Molaei et al. 2009)
(Damiens et al. 2014)
(Schonenberger et al. 2016)
(Apperson et al. 2004)

Appendix 4: Hosts for Aedes japonicus
Host
Birds &
Mammals
Birds &
Mammals

Humans
Humans
Cat
Chickens

Observed feeding habits
Aedes japonicus fed readily on chicks and mice but
did not feed on both reptiles and amphibians.
Mammals: New World camelid , human, sheep,
donkey, harbour seal, Indian lion, nilgai,
Avian: chicken, Darwin’s rhea, blackbird, house,
sparrow, Humboldt’s penguin, unknown bird species
Mixed: house sparrow and New World camelid
H. japonica and Aedimorphus vexans (=Aedes
vexans) are the most likely candidate bridge vectors
for WNV transmission in Switzerland.
readily feed on humans,
readily feed on humans, regularly receive complaints
about biting nuisance.
The single bloodfed Ae. japonicus collected fed on a
domestic cat (Felis catus L.).
Feed on chickens infected with WN virus isolated
from a crow that died during the 1999 outbreak.

Page 29 of 34

Reference
(Miyagi 1972)
(Schonenberger
et al. 2016)

(Molaei et al.
2009)
(Schaffner et
al. 2011)
(Westby et al.
2015)
(Turell et al.
2001b)

RIVM Letter report 2018-0091

Page 30 of 34

RIVM Letter report 2018-0091

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