Status:  Final    
 Rapid Technical Advice Japanese encephalitis on live horses from Australia ◦ 1 
Early release of Japanese encephalitis chapter from the (draft) 
IRA live equids 2022  
Date:  10 March 2022  
Name:  Fanny Leduc  
Position:  Senior Adviser, Animal Risk Assessment  
Background  
Biosecurity New Zealand (BNZ) is currently assessing its risk management measures on live 
horses from Australia with regards to the recent change of distribution of Japanese encephalitis (JE) within that country. The animal risk assessment team has been involved in providing information to support this work.  On the 3
rd March 2022 a rapid technical advice 
was produced to specifically assess the risk from Australia.  
The technical information in the rapid technical advice was mostly taken from the JE chapter from the draft IRA for live equids that is currently being written. The IRA will be signed off and published in the next few weeks. However, there is a need to make the JE draft chapter available early to support work from various teams at BNZ. 
The current version of the chapter is copied below. It  has undergone external peer -review and 
the subject matter experts did not have comments on the chapter. It is therefore likely that the 
text will not change before publication of the IRA. 
Please note that the risk assessment from the IRA is slightly diffe rent than that for the rapid 
technical advice. This is mostly because the commodity definition is different. For the IRA, 
the commodity definition is domestic equids from all countries, with a goal of producing a generic import health standard. For the rapid technical advice, the commodity definition is horses from Australia, taking into account the import certificate currently in use for that 
country. 
This document will be signed off by the relevant managers for internal or external use as 
required. Please see the signature section below to determine which level of approval has been obtained.  
14. Japanese encephalitis  
14.1 Technical  review  
14.1.1  Aetiology  
Family: Flaviviridae Genus: Flavivirus  
Japanese encephalitis virus  (JEV) (ICTV, 2019)  genotypes I to V (OIE, 2019)  
14.1.2  OIE list  
Japanese Encephalitis (JE) is an OIE -listed disease affecting multiple species (OIE, 2021a) . Status:  Final    
 Rapid Technical Advice Japanese encephalitis on live horses from Australia ◦ 2 
14.1.3  New Zealand  status  
JEV has never been reported in animals in New Zealand  (OIE, 2021b) . It is an unwanted and 
notifiable organism (MPI, 2021) . 
14.1.4  Zoonotic potential  status  
JE has been reported in humans, who are considered accidental, dead -end hosts  who cannot 
transmit the virus . Approximately one in 250 human JEV infections show clinical disease, 
while the remain der are asymptomatic.  It is reported that 20–30% of clinically affected 
patients die, and a further 30–50% have continuing neurological symptoms following 
recovery (Amicizia et al., 2018) . 
14.1.5  Epidemiology  
Host range  
The primary lifecycle fo r JEV involves cycling between mosquitoes and birds (mostly of the 
Ardeidae  family – herons and egrets) or pigs. Although transovarial transmission has been 
documented in mosquitoes which allows some level of spread to occur, birds and pigs act as amplifying hosts and are the main reservoir of infection (Bhattacharya & Basu, 2014; Delcambre & Long, 2014) . 
Humans and equids have frequently been documented to be affected with clinical disease caused by JEV, but do not have sufficient viraemia to subsequently infect mosquitoes and are therefore considered dead- end hosts (Amicizia et al., 2018; Bhattacharya & B asu, 2014; 
Delcambre & Long, 2014) . 
Numerous other species have been studied to determine their implication in the epidemiology of JE. In birds, there is some evidence that chickens, ducks, pigeons, sparrows and other passerines could have sufficient vir aemia to be amplifying hosts. Some snakes, freshwater 
turtles, bats and flying foxes have also tested positive for JE infection and some authors suggest they may be maintenance hosts (Bhattacharya & Basu, 2014) . Migratory birds may 
have a role to play in disseminating the virus regionally (Miller et al., 2012) . 
Antibodies have been detected in cattle, goats, dogs and cats, but they are rarely or never affected by clinical disease and are also considered dead -end hosts (Bhattacharya & Basu, 
2014; Mansfie ld et al., 2017) . 
Geographical distribution  
The distribution of JE is usually described by monitoring and reporting human cases. In humans the disease tends to be related to the seasonality of the transmitting mosquito species, the water environment the mosquitoes live in such as rice paddies, and the proximity to pigs. The disease is endemic in tropical and subtropical regions of Asia, from southern India to Papua New Guinea and northern Queensland (Australia), with cases reported all year round. Epidemi c areas are those where the disease is infrequent and usually seasonal and lie to the 
north of the endemic area, from Pakistan to Japan  (Wang & Liang, 2015) . 
Disease in horses has been reported in Pakistan, India, Sri Lanka, Thailand, China, Nepal, Taiwan, Malaysia, Brunei, the Philippines, Australia and Japan (Delcambre & Long, 2014; 
Mansfield et al., 2017) . Status:  Final    
 Rapid Technical Advice Japanese encephalitis on live horses from Australia ◦ 3 
Pathogenesis  
Incubation can last from 4–14 days but is generally 8–10 days in horses (OIE, 2019) . 
Viraemia is short- lived and animals and humans  rapidly develop an immune response 
following infection. Immunity is thought to be lifelong (Bhattacharya & Basu, 2014; 
Mansfield et al., 2017) . Maternal antibodies can be detected in piglets for up to eight months 
(OIE, 2021c) . A state of persistent infection has not been reported in mammals or birds. 
As in humans, infection with JEV in horses is usually subclinical. Clinical disease is considered rare in horses and clinical signs consist of fever, neurological signs and occasionally death (Delcambre &  Long, 2014; Mansfield et al., 2017) . In pigs the infection is 
also mostly asymptomatic, but when signs are present, they mostly affect pregnant sows and include fever, anorexia, abortions and congenital defects (Delcambre & Long, 2014; Mansfield et al.,  2017) . Clinical disease has not been reported in birds.  
Transmission  
The recognised route of transmission between animals is via known arthropod vectors , 
namely Culex mosquitoes . There is one report of iatrogenic transmission to two 
immunocompromised humans via blood products (Cheng et al., 2018) . 
More than 30 species of mosquitoes have been implicated in the spread of JEV. Further interaction between those mosquitoes and the amplifying hosts are required for effective 
spread of the virus. The relationships between the mosquitoes, amplifying hosts a nd incidental 
hosts such as humans and horses are not fully understood (Oliveira et al., 2018) . 
The main mosquito vector is Culex tritaeniorhyncus , which has a distribution closely related 
to areas where rice cultivation is practiced and cases of JE in h umans are reported (Miller et 
al., 2012) . Other known competent vectors of the Culex family include Cx. vishnui , 
Cx. pseudovishnui , Cx. gelidus , Cx. fuscocephala, Cx. quinquefasciatus , Cx. annulus , 
Cx. annulirostris , Cx. annulirostris marianae , Cx. pipie ns and possibly Cx. sitiens . Some 
mosquitoes of the Aedes  and Anopheles  families have also been implicated (Mansfield et al., 
2017; Wang & Liang, 2015) . 
In 2016, a series of studies were published showing that experimentally infected pigs were 
able to tr ansmit the virus to naïve pigs in the absence of arthropod vectors. Although this 
phenomenon is yet to be reported in naturally occurring disease outbreaks, the authors believe this mode of transmission could explain reports where the virus was able to rea ppear 
seasonally or a few years later in temperate regions (Ricklin et al., 2016) . 
Diagnosis  
As many viruses can cause neurological signs in horses, diagnosis cannot  be based on clinical 
examination alone. Definitive diagnosis requires laboratory techniques. As viraemia is short, in horses a definitive diagnosis can generally only be reached via virus isolation on nervous tissue samples of deceased individuals. Test s ensitivity using this technique may be low, 
possibly due to the instability of the virus in the samples. A disease investigation will likely also include the detection of antibodies in the serum or cerebrospinal fluid (CSF) (Mansfield et al., 2017; OIE, 2021) . Status:  Final    
 Rapid Technical Advice Japanese encephalitis on live horses from Australia ◦ 4 
Agent identification tests available include virus isolation in various cell cultures or live mice, 
antigen detection by agglutination or via real -time RT -PCR. Serological tests to detect an 
immune response include haemagglutination inhibition, complement fixation, ELISA, virus neutralisation and indirect immunofluorescence assay test (IFAT), possibly using paired sera to show an increase in titer (Mansfield et al., 2017; OIE, 2021) . All serological tests have 
cross -reactivity to other flaviviruses , and in regions where other viruses of the JE serogroup 
can be present (such as West Nile fever or Murray Valley encephalitis), diagnostic tests for these agents should also be undertaken (OIE, 2021) . 
Treatment, prevention and control  
There are no pharm acological treatments available for JE in horses. Supportive care of 
affected individuals is all that can be provided (Delcambre & Long, 2014) . 
Vaccination has been the main tool utilised for prevention, especially in humans, horses and pigs (Mansfield et al., 2017; Nah et al., 2015; Wang & Liang, 2015) . The OIE Manual 
contains requirements for manufacturing vaccines. The Manual states that in A sia, an 
inactivated vaccine is available for horses, while two vaccines are available for pigs (one inactivated, the other live attenuated) (OIE, 2021) . Vaccines in animals are generally used to 
reduce production losses in pigs and ill -health effects or deaths in valuable horses.  
Insecticides and larvicides can be used to reduce mosquito populations locally but costs and impacts on non- target species mean that vector control has limited use in practice (Mansfield 
et al., 2017) . 
14.2 Risk assessment  
14.2.1 Entry assessment  
Japanese encephalitis infection only occurs in some countries. In endemic areas, clinical cases in horses are rare and most infections remain subclinical and undetected. The OIE deems the incubation to be 21 days (OIE, 2021d) . In hors es, viraemia only lasts a few days, followed by 
seroconversion with lifelong sterile immunity.  
There are few reports of seroprevalence for JE in horses in Asia but depending on the region it could range from 10–90% (Gulati et al., 2011) . 
The likelihood of entry of JE in incubating or viraemic live horses is very low. 
14.1.2  Exposure assessment  
Horses are dead -end hosts that cannot transmit the infection to mosquito vectors, birds, other 
mammals or humans. Literature has established that horses cannot be a pathway for 
establishment of new transmission cycles (Pfeffer & Dobler, 2010) . 
The likelihood of exposure, establishment and/or spread of JE in New Zealand following the importation of an incubating or viraemic horse is negligible. Status:  Final    
 Rapid Technical Advice Japanese encephalitis on live horses from Australia ◦ 5 
14.1.3  Risk estimatio n 
The likelihood of entry is very low and the likelihood of exposure, establishment and/or 
spread is negligible. Therefore, under the methodology used in this risk assessment  the biosecurity risk is negligible and risk management measures are not justifie d. 
New Zealand is historically free from JE. To maintain this freedom (as per Article 1.4.6 of the OIE Code), adherence to Chapter 8.10 would need to be considered. Article 8.10.2 is included in Appendix 1 for future reference.  [Appendix from IRA not suppl ied here. Please refer to the 
OIE Code as required]  
Sign off:  
Version 
number  Approved for internal use by: Approval date:  
V 1.0  
 
Jiss Job, Manager (acting), Animal Risk Assessment Team  
Animal and Plant Health Directorate  
Biosecurity New Zealand  
Ministry for Primary Industries  11/03/2022  
 Approved for external release by:  
EPerotti  
Enrico Perotti, Associate Director, Risk Assessment Group  
Animal and Plant Health Directorate  
Biosecurity New Zealand  
Ministry for Primary Industries  11/03/2022  
Comments:  Noting that this is an early release extracted from version 1 of the live equids IRA (2022). 
There might be updates and changes in the final release of the IRA (including this chapter).  
Document storage 
This draft Scientific and technical advice document is stored in the Biosecurity library in 
Piritahi: Early release of Japanese encephalitis risk assessment chapter March 2022.docx 
(cohesion.net.nz)  
References  
Amicizia, D; Zangrillo, F; Lai, P L; Iovine, M, & Panatto, D (2018) Overview of Japanese encephalitis disease and its prevention. Focus on IC51 vaccine (IXIARO ®). Journal of Preventive Medicine and Hygiene, 59(1): E99 -E107. doi:10.15167/2421-
4248/jpmh2018.59.1.962  
Bhattacharya, S, & Basu, P (2014) Japanese encephalitis vi rus (JEV) infection in different 
vertebrates and its epidemiological significance: a review. International Journal of Fauna and Biological Studies, 1(6): 32- 37.  
Status:  Final    
 Rapid Technical Advice Japanese encephalitis on live horses from Australia ◦ 6 
Delcambre, G H, & Long, M T (2014) Flavivirus encephalitides. In Sellon, D C, & Long, M 
T (Eds .) Equine Infectious Diseases. (2nd ed., pp. 217- 226) Saunders: USA. 
doi:10.1016/C2010- 0-67112- 4 
ICTV (2019) Taxonomy. https://talk.ictvonline.org/taxonomy/. Accessed 3 July 2021. 
Mansfield, K L; Hernández -Triana, L M; Banyard, A C; Fooks, A R, & Johnson, N (2017) 
Japanese encephalitis virus infection, diagnosis and control in domestic animals. Veterinary 
Microbiology, 201: 85- 92. doi:10.1016/j.vetmic.2017.01.014 
MPI (2021) Pest register for New Zealand importers. https://pierpestregister.mpi.govt.nz/PestsR egister/ImportCommodity/. Accessed 10 July 2021. 
Nah, J; Yang, D; Kim, H, & Song, J (2015) The present and future of veterinary vaccines for Japanese encephalitis in Korea. Clinical and Experimental Vaccine Research (Seoul), 4(2): 130-136. doi:10.7774/cevr .2015.4.2.130 
OIE (2019) Japanese encephalitis. https://www.oie.int/fileadmin/Home/eng/Animal_Health_in_the_World/docs/pdf/Disease_cards/JAPANESE_ENCEPHALITIS.pdf. Accessed 5 March 2021.  
OIE (2021a) Animal diseases. https://www.oie.int/en/what -we-do/animal -health -and-
welfare/animal -diseases/?_tax_diseases=oie- listed. Accessed 6 May 2021.  
OIE (2021b) Disease situation dashboard. https://wahis.oie.int/#/dashboards/country- or-
disease- dashboard. Accessed 6 August 2021. 
OIE (2021c) Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2021. https://www.oie.int/en/what- we-do/standards/codes -and-manuals/terrestrial- manual -online -
access/. Accessed 13 July 2021. 
Ricklin, M E; García -Nicolás, O; Brechbühl, D; Python, S; Zumkehr, B; Nougairede, A; 
Charrel, R N; Posthaus, H; Oevermann, A, & Summerfield, A (2016) Vector -free 
transmission and persistence of Japanese encephalitis virus in pigs. Nature Communications, 
7(1): 1 -9. doi:10.1038/ncomms10832 
Wang, H, & Liang, G (2015) Epidemiology of Japanese encephaliti s: past, present, and future 
prospects. Therapeutics and Clinical Risk Management, 11: 435- 448. 
doi:10.2147/TCRM.S51168