Japanese Encephalitis Virus

In recent months you may have heard about the Japanese Encephalitis Virus (JE) which has been detected in Eastern Australia. The JE is a mosquito borne viral disease associated with the inflammation of the brain (encephalitis) in susceptible species, of which horses are among. 

The JE is spread by mosquitoes feeding on infected animals, but generally other animal species cannot spread it to other animals or humans. In other words, the virus is not contagious. In some cases, if a mosquito bites an infected animal that has JE, the virus will transmit back to the mosquito. However, horses are considered to be an end host for the JE, as they do not gain enough of the virus within their blood, and so cannot transmit it back to mosquitoes. 

Generally, horses don’t show any symptoms when they are infected with JE, and if they do, then the clinical signs will tend to be mild. However, in rare cases, more severe encephalitis can occur which can be fatal. If a horse is symptomatic with JE, it may show the following signs:

• Fever
• Refusal to eat (anorexia)
• Neurological signs (lack of coordination, impaired vision, difficulty swallowing and in some cases hyperexcitability)

If your horse is showing any signs of JE it is important to contact your vet immediately.

There are some measures that you can take to protect your horse against mosquito bites, and reduce infection of JE. The mosquito that carries JE is generally active during the summer and autumn months and feeds between dawn and dusk. So, it is recommended stabling your horse during these times to reduce infection.  If you are stabling your horse at night, you can further reduce mosquitos from coming into the barn by:

• rugging your horse to prevent mosquito bites;
• installing overhead fans or misting systems;
• installing mesh barriers on stable openings (such as in the case of walk in/walk out stables);
• turning off stable lights at night to discourage mosquitos from entering;
• place incandescent bulbs around the stable perimeter to attract mosquitos to those locations; and
• use repellents (chemicals) to deter mosquitos from the stable area.

If you are not able to bring your horse inside a stable, then there are other measures that you can take to reduce the risk of contracting JE. These include:

• Rugging horses to create a physical barrier to prevent mosquito feeding;
• eliminating or controlling mosquito breeding sites; and
• using a repellent on your horse and/or the rug, ensuring that the repellent is safe to use on your horse, whilst also being effective at deterring mosquitos. 

Currently there are no known reported cases of JE in Western Australia. A vaccine is available for horses against JE, however currently none have been approved for use in Australia.