Equine Encephalitis

What is Equine Encephalitis?

Equine Encephalitis is a rare viral mosquito-borne disease. Eastern Equine Encephalitis (EEE) is caused by eastern equine encephalitis virus, Western Equine Encephalitis (WEE) is caused by western equine encephalitis virus and Venezuelan Equine Encephalitis (VEE) is caused by Venezuelan equine encephalitis virus. Equine Encephalitis can affect the central nervous system and cause severe complication and death. Symptoms range from mild flu-like illness (like headache, malaise, fever, vomiting and stiff neck) to frank encephalitis, coma and death. It is endemic in North, Central and South America.

Case fatality rate of EEE is 35% and it is estimated that 35% of people who survive EEE will have mild to severe neurologic deficits. Case fatality of WEE is 3% and neurologic sequalae is seen in 13% of infected people, more common in children. Case fatality rate of VEE is less than 1%, although is higher in the very young or aged.

How does it spread?

Equine Encephalitis is transmitted to humans through the bite of an infected mosquito. The main EEE transmission cycle is between birds and mosquitoes. Several species of mosquitoes can become infected with EEE virus. WEE virus has a complex lifecycle involving birds and a specific type of mosquito, Culex tarsalis, that is common in farming areas and around irrigated fields. VEE has a zoonotic reservoir in bats, birds, rodents, horses, and donkeys. The principal vector for humans is Aedes aegypti.

Anyone can get equine encephalitis, but people living in or visiting endemic areas and those who work outside or participate in outdoor recreational activities in endemic areas are at increased risk.

How can you prevent it?

At present, vaccine is only available for horses but not for human. Travellers must therefore rely on preventing mosquito bites to combat infection (especially during their high biting activity time). The personal protection measures against mosquito bites are as follows:-.

  • Wear long-sleeved shirts and trousers;

  • Rest in air-conditioned or well-screened rooms;

  • Use aerosol insecticide indoor and use bednets if sleeping areas are not air-conditioned or screened;

  • Use insect repellents containing DEET (for children keep DEET concentration below 20%) on exposed skin;

  • If travelling in endemic rural areas, carry a portable bed-net and apply permethrin on it as well as to clothes.

How is it treated?

There is no specific treatment for Equine Encephalitis. Care of patients centers on treatment of symptoms and complications.



Last revision date: 10 October 2012