Biosecurity Alert - First detection of Japanese encephalitis in Australian pigs in 2022-23

First detection of Japanese encephalitis in Australian pigs in the 2022-23 season

BIOSECURITY ALERT FROM VICTORIAN CHIEF VETERINARY OFFICER ISSUED 22 NOVEMBER 2022

Japanese encephalitis (JE) has been confirmed in a New South Wales piggery. JE viral fragments were detected by PCR in tissue samples collected from a litter of still-born piglets. This is the first detection of JE in Australia in the 2022-23 season.

The disease has not been detected in any Victorian livestock at this time.

Agriculture Victoria has been closely monitoring the situation, actively continuing to investigate and test horses and pigs or other livestock (for example, alpaca) presenting with clinical signs consistent with JE virus infection. This work was ramped up in September 2022 but testing to date has not detected the presence of the disease in Victoria.

JE is a notifiable disease of livestock nationally. This means that in Victoria you are required to notify Agriculture Victoria immediately on suspicion of disease through your local Agriculture Victoria Animal Health and Welfare team, the Emergency Animal Disease Watch Hotline 1800 675 888 or the Notify Now App.

To ensure that suspect cases in livestock can be promptly investigated, veterinarians and producers can receive financial support for submission and testing of samples under the Significant Disease Investigation (SDI) program. See https://agriculture.vic.gov.au/biosecurity/animal-diseases/significant-disease-investigation-sdi-program

Background

Japanese encephalitis is an acute mosquito-borne viral disease that can cause reproductive losses and encephalitis in susceptible species. Disease occurs most commonly in pigs and horses but can also rarely cause disease in other animals.

Animals and people become infected through the bite of infected mosquitoes. The disease is maintained and spread through transmission cycles between mosquitoes (Culex, Aedes and Anopheles genera) and some wild and domestic bird species and pigs.

Clinical signs of JE in animals

In pigs, the most common clinical signs are abortion, 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. Adult sows do not typically show overt signs of disease, and boars, if present on the 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. REMINDER: Hendra virus infection must always be ruled out in cases of neurological disease in horses.

Japanese encephalitis was reported in an alpaca in South Australia earlier in 2022 but reports of the disease in other species are rare.

JE in people

JE virus is transmitted to humans through infected mosquitoes. Most JE virus infections in people are asymptomatic. However, encephalitis is the most serious clinical consequence of JE virus infection. 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. Vaccination is available in Victoria for high-risk groups. Advice from the Department of Health on the disease and its prevention is available at: Japanese encephalitis virus (health.vic.gov.au)

People experiencing symptoms of JE should seek medical advice and contact the Communicable Disease Prevention unit at the Department of Health on 1300 651 160 (24 hours).

What to do to prevent the spread of JE around livestock

Prevention depends heavily on effective vector control and/or avoidance of mosquito bites. Relevant Australian reference materials are available on mosquito management and control for both pigs and horses. These can be found on the following Farm Biosecurity websites:

Actions to take if you suspect Japanese Encephalitis in your client’s animal

Japanese encephalitis is a notifiable exotic disease in Victoria. If you suspect Japanese encephalitis in any animal, but especially in pigs or horses showing the signs described above, immediately contact your local Agriculture Victoria staff or phone the all-hours Emergency Animal Disease Watch Hotline (1800 675 888).