Japanese encephalitis

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Japanese Encephalitis

Japanese encephalitis (JE) is caused by infection with the japanese encephalitis virus (JEV), a mosquito-borne virus found predominately in Asia and the Pacific Islands. The epizootic/epidemic JE season in northern Asian temperate climates usually begins in May or June, and ends around September or October. Endemic JE virus circulates year-round in tropical areas of Asia among birds, swine and mosquitoes.

Three types of manifestations of JEV can occur---transitory, lethargic, or hyperexcitable. Clinical signs, if present, vary; disease usually presents itself in sporadic or localized clusters.

Mosquitoes belonging to the genera Culex and Aedes transmit the virus. Other genera have also been shown to harbor the virus but their role in transmission remains unconfirmed. Vertical transmission occurs in mosquitoes.

Incubation Period
The incubation period is 8–10 days. Most infected horses do not show clinical signs of the disease.


Loss of appetite
Difficulty swallowing
Transient neck rigidity
Impaired vision
Aimless wandering
Violent and demented behavior
Profuse sweating
Muscle tremors
Staggering and falling
Loss of appetite


  • History
  • Clinical signs
  • Physical exam
  • Laboratory tests


Report diseaseJE is a reportable disease, meaning that if you suspect that your horse has this disease, by law you need to report it to your veterinarian, or a state or federal veterinarian.
Supportive care


  • Vaccination
  • Biosecurity


Morbidity rates reported from field cases vary from less than 1% to 1.4 %. Case fatality rate in outbreaks can vary from 5 to 15% but can reach 30–40% in more severe epizootics.

Scientific Research References

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