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Japanese B. Encephalitis (JBE)

(543) Japanese B. encephalitis (JBE) is caused by a virus (a member of the flavivirus group) which is spread by mosquitoes. The pig is the natural amplifier and reservoir host. In other words it serves to multiply up the virus and keep it going. Many other species can be infected including most domestic animals and many wild animals such as rabbits, mice, birds, bats, snakes and lizards.

Should you be concerned about JBE?

You should be if you work in South Asia or visit pig farms there.

JBE is confined to a large area of South Asia, about 6500 x 6500km (4000 x 4000 miles), centred on the China Sea and stretching from Ceylon to Japan and from New Guinea to Mongolia and Eastern Russia. This includes such major pig producing countries as China, Taiwan, Korea, Thailand, the Philippines and Japan.

If you live outside this area of South Asia, there is no risk to your herd and no risk to you unless you decide to visit pig farms in the area, in which case get yourself vaccinated twice, preferably three times, before you go.

Importance of JBE

JBE is not a very important disease of pigs causing only sporadic reproductive problems.

Its main importance is its threat to public health.

Clinical signs

The main clinical signs are degeneration of the boar's testicles and infertility and the birth of abnormal piglets. These include mummified foetuses, dead piglets with subcutaneous oedema (excess clear bodily fluid under the skin), hydrocephalus (water on the brain), and weak piglets sometimes with nervous signs.


This requires laboratory examination of dead stillborn piglets and affected boars' testicles.

Definitive diagnosis depends on the isolation of the virus in tissue culture and demonstration of antibodies in stillborn piglets serum, usually by an ELISA.

Similar reproductive problems are caused commonly by parvovirus, aujeszky's disease, PRRS, certain strains of influenza, CSF(hog cholera), and some enteroviruses.

There are no specific lesions visible to the naked eye.


  • There is no effective treatment.
Management control and prevention
  • Vaccination - In countries in which this disease is endemic young breeding gilts and boars are vaccinated twice before the mosquito season starts commonly with an attenuated vaccine but inactivated vaccines are also available.
  • Trying to control mosquitoes in pig herds is a waste of time.

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