Japanese encephalitis

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Japanese Encephalitis

Japanese encephalitis (JE) is an acute arbovirus disease which causes encephalitis in horses and humans, and abortion in pigs. It is caused by infection with the japanese encephalitis virus (JEV), a mosquito-borne virus which occurs in widely dispersed areas in eastern Asia, including Papua New Guinea and Indonesia. The virus was introduced into the Torres Straight Islands in 1995 and to the Australian mainland in 1998. JE originated in Japan, with first known outbreaks occurring as early as 1871 and the virus was first isolated in 1935. 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.

How JE is Transmitted to Horses

The virus is transmitted to horses through biting insects. One of the main mosquito vectors is Culex annulirostris in Queensland, Australia.


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

General Overviews

Risk Factors

  • Horses living in Asia and Australia, especially any imported from Japan.