Date Updated: April 22, 2022

Japanese encephalitis is a viral brain disease transmitted by mosquitoes infected with the virus from animals to humans. As of April 2022, 24 human cases of Japanese encephalitis have been confirmed with 10 cases in NSW.

How does Japanese encephalitis spread?

The principal source of viral spread is through water birds such as herons and egrets. Pigs can also produce enough of the virus to infect mosquito populations for around four days. Although horses can be infected by the virus, they are considered a ‘dead end host’ meaning they don’t pass on the virus to mosquitos.

It is uncommon for the disease to affect other animals and they typically do not show any symptoms of infection. Animals infected with the virus do not spread it to other animals.

The virus is spread to humans when an infected mosquito comes into contact with an individual. It is important to remember that humans cannot pass the virus between one another.

What symptoms should you look out for?

Adult sows typically do not show overt symptoms of the virus. However, when infected they often give birth to stillborn or weak piglets.

Most cases of Japanese encephalitis in horses are mild. The following symptoms may be seen:

• Fever
• Jaundice
• Lethargy
• Anorexia
• Incoordination
• Difficulty swallowing
• Impaired vision

Most cases in humans are asymptomatic. Early symptoms in humans may include headaches, fever and vomiting.  In severe cases signs of encephalitis such as neck pain can occur.  This may progress to convulsions or coma.  In rare cases, the virus can progress to the point of irreversible brain damage or death.

What steps should animal owners take?

Mosquito management should be practiced by anybody dealing with pigs, even those who only have a small herd or a pet.

Horse owners should also take precautions to keep their horses safe from mosquito bites:

• During the warm months, cover the horses’ back with a light cotton rug
• Apply a fly mask
• If the horse permits, use a safe bug repellent. Spray the repellant away from eyes and face.

As these mosquitoes often feed at night, stabling horses between nightfall and morning is beneficial.

How can you treat Japanese encephalitis?

Unfortunately, there is no treatment or vaccine for animals against Japanese encephalitis. A vaccine is available for humans. However, the most effective treatment is breaking the transmission cycle by reducing mosquito habitats and exposure to mosquitos.

The majority of human cases of Japanese encephalitis have no or extremely minor symptoms, but if you experience a rapid onset of fever, headache, or vomiting seek medical attention immediately.

To report suspected Japanese encephalitis in pigs or other animals, contact your local veterinarian or call the national Emergency Animal Disease Watch Hotline on 1800 675 888.