Japanese Encephalitis Virus

Also Known As: JE — Japanese B Encephalitis — Hydrancephaly — JEV — JE Virus

Introduction

Japanese Encephalitis is caused by a mosquitoe-borne flavivirus and affects a wide range of species including ruminants, carnivores, birds and humans.

It is best known for causing reproductive failure in sows and central nervous system disease in horses. Pigs are the main amplifying host.

This disease is notifiable to the World Organisation for Animal Health (OIE)

JE is zoonotic, epidemics having been recorded in Japan, Korea and India during the mosquito season. Although disease is usually mild or subclinical, fatal encephalitis can develop in children.

Distribution

JE has a number of insect vectors, mainly mosquitoes. Distribution is restricted to South-East Asia.

Birds, particularly herons, are maintenance hosts for JEV while pigs are amplifier hosts.

Clinical Signs

Key reproductive signs include abortion in pregnant sows, stillbirths, male infertility, lack of libido, small litter sizes and heat on palpation of the testes and scrotum.

Neurological disease in horses features trembling, ataxia, incoordination, opisthotonus, hypermetria, aggression and blindness.

Anorexia, inappetance and ill thrift often accompany other signs.

Infection is usually subclinical in other species.

Diagnosis

Antibody titres can be detected serologically by haemagglutination inhibition, ELISA, serum neutralisation and other methods. Antibodies can also be detected in foetuses.

Viral antigen can be demonstrated in brain, placenta and foetuses by indirect fluorescent staining (IFAT) and avidin-biotin staining.

On post-mortem of piglets from infected dams, hydrocephalus, hydrothorax, subcutaneous oedema and necrotic foci within the organs are common. The meninges and spinal cord may be congested and cerebellar hypomyelinogenesis has been described.

In male infected pigs, large amounts of mucoid fluid are present within the tunica vaginalis and the epididymis and tunic are fibrosed.

Treatment

No treatment is available in animals.

Human recombinant interferon has been used in human cases of JEV.

Control

Live attenuated vaccines are available against JEV. A human vaccine is available and should be given to those at high risk of exposure to infection.

Fly control is valuable but impractical.

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References

This article was originally sourced from The Animal Health & Production Compendium (AHPC) published online by CABI during the OVAL Project. The datasheet was accessed on 6 June 2011.