Japanese B Encephalitis

Japanese B encephalitis is caused by a virus found in South Asia, it is transmitted by mosquitoes and appears as a reproductive problem.


Japanese B encephalitis is caused by a virus transmitted by mosquitoes. The disease is confined to a large area of southern Asia. It can affect most domestic animals and in humans it produces encephalitis. The pig is an important source of infection.




  • No clinical effects.


  • Infertility.
  • Testicular degeneration.

Lactation piglets

  • Mummified fetuses.
  • Stillbirths.
  • Subcutaneous edema.
  • Hydrocephaly.
  • Weak piglets.
  • Neurological symptoms in piglets - attacks and seizures.

Nursery and fattening

  • No clinical effects. 


Causes / Contributing Factors

  • Presence of  mosquitos.
  • Susceptible pigs.
  • Other species that act as reservoirs of the virus.



  • Lab tests of stillbirths and of testes from affected boars.
  • Definitive diagnosis requires tissue culture virus isolation, and serum antibodies from stillbirths, usually using ELISA.
  • Differentiate from other similar reproductive problems as those caused by parvovirus, Aujeszky's disease, porcine reproductive and respiratory syndrome, some strains of influenza, classical swine fever and some enteroviruses. 



  • There is no effective treatment.
  • Vaccination.

Atlas of pathology

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