What is Japanese encephalitis (JE)?
Japanese encephalitis (JE) is a mosquito-borne viral disease that can cause reproductive losses and encephalitis in susceptible animal species. It is caused by Japanese encephalitis virus which is a member of the Flavivirus genus.
How is JE spread?
The virus is primarily spread by mosquitoes feeding on infected animals and does not usually spread directly from animal to animal (i.e. it is not considered contagious). Certain types of mosquitoes can become infected with JE such as Culex sp. and these tend to most active at dawn and dusk.
Animals with the infection do not transmit the infection to other animals but may infect mosquitoes if bitten while they still have the virus in their blood.
In general, spread is through the movement of migratory birds and through the movement of infected mosquitoes, often over long distances due to wind dispersal.
Which animal species are affected by JE?
JE disease occurs most commonly in pigs. Horses can also be infected and rarely other animals.
Pigs and waterbirds such as herons and egrets are an important part of the transmission cycle as they can amplify the virus and provide an ongoing source of JE to infect local mosquito populations.
What are the clinical signs of JE?
In pigs the most common clinical signs are mummified and stillborn or weak piglets, some with neurological signs. In a naïve population, litters from sows and gilts would be expected to be equally affected. Piglets infected after birth can develop encephalitis (paddling, other neurological signs) in the first six months of life. In other cases, wasting, depression or hindlimb paralysis may be seen in suckling piglets and weaner piglets. Adult sows do not typically show overt signs of disease, and boars, if present on farm, may experience infertility and oedematous, congested testicles.
In horses many cases are asymptomatic and most clinical disease is mild, however more severe encephalitis can occur which may be fatal. Signs include fever, jaundice, lethargy, anorexia and neurological signs which vary with severity of the clinical disease. Neurological signs can include incoordination, difficulty swallowing, impaired vision, and rarely a hyperexcitable form occurs. Disease has also been reported in donkeys.
Reports of disease in other species are rare and affected animals may show non-specific clinical signs such as fever and decreased appetite or neurological signs.
What are the human symptoms of JE?
The majority (about 99%) of JE infections in people cause no symptoms. Some infected people experience an illness with fever and headache. Those with a severe illness may experience neck stiffness, disorientation, tremors, coma, convulsions (especially in children) and paralysis. JE can cause permanent neurological complications or death.
Symptoms (if they do occur), usually develop 5 to 15 days after being bitten by infected mosquitoes.
Children aged under 5 years old and older people who are infected with JE are at a higher risk of developing more severe illness, such as encephalitis.
People experiencing symptoms should seek medical advice and contact the Communicable Disease Prevention unit at the Department of Health on 1300 651 160 (24 hours).
How can I protect myself from JE?
The best protection is to avoid mosquito bites by using mosquito repellent containing picaridin or DEET on all exposed skin, wearing long, loose fitting clothing when outside, and ensuring accommodation, including tents, are properly fitted with mosquito nettings or screens.
People with increased exposure to mosquitoes may be at a higher risk of infection, particularly those in regional areas and who work with or are in contact with pigs, and people camping, working or spending time outdoors in these regions.
I think I have JE – What should I do?
Most people with JE will have no or very mild symptoms, but anyone who develops a sudden onset of fever, headache and vomiting should see their doctor immediately.
People with these symptoms can deteriorate over just a few short days, including suffering a loss of coordination, disorientation, generalised weakness and issues with movement which may last for years.
What to do if I suspect JE in my animals?
Japanese encephalitis is a notifiable exotic disease in Victoria. If you suspect Japanese encephalitis in any animal, but especially in pigs or horses showing any clinical signs, immediately contact your local Agriculture Victoria staff or phone the all-hours Emergency Animal Disease Watch Hotline (1800 675 888).
How can I reduce the risk of spread?
JE is spread through biting insects or management practices that involve penetrating the skin, e.g. vaccination, blood collection, etc. Infected animals should be kept isolated.
Insecticide can be applied to reduce insect numbers and minimise further spread of the virus.
To minimise the risk of spreading the virus through management practices avoid sharing needles between animals when injecting and thoroughly wash and decontaminate other equipment between animals. Reducing mosquito habitats and exposure to mosquitos is an important part of breaking the transmission cycle.
What is the government’s response to JE?
The Victorian Government is working to understand the extent of JE in domestic animal populations and advise on measures that can reduce spread in order to support public health agencies and minimise economic impacts. Agriculture Victoria is working closely with Department of Health to coordinate public health response activities. A number of activities may be undertaken, including:
Quarantine and movement controls for infected livestock
Tracing and surveillance to determine the source and extent of infection.
Advice and guidance to industry on treatments and husbandry procedures to control insect attacks, minimise health and production effects and provide animal welfare relief
For information related to public health please visit the Victorian Department of Health website or Better Health Channel on Viral encephalitis.