Japanese Encephalitis

The report of Japanese encephalitis in Korea among recently imported horses re-emphasizes the serious consequences that can occur following the international movement of horses if appropriate preventive measures are not taken. Japanese encephalitis is a mosquito-borne viral disease affecting mainly pigs, horses, and humans. It causes abortion in pigs and fever and encephalitis with death in horses and humans.

The disease is widely distributed in Asia, including countries such as Japan, Korea, Thailand, Malaysia, and India (which in recent times have increased the number of horses they import from North America), plus Australasia and Europe. Horses imported from these countries have never been exposed to this virus and are therefore completely susceptible to the disease, particularly during the “rainy summer season” when the risk of mosquito transmission is higher.

An inactivated vaccine against the disease used in Japan since 1948 has significantly reduced mortality among horses over the years, and horses in Hong Kong and Singapore are routinely vaccinated against Japanese encephalitis. The only source of equine vaccine is currently from Japan, although a live vaccine is utilized in China. However, it would seem prudent to advise those who import horses from Asian and Pacific Rim countries from outside that region to vaccinate all horses on arrival against Japanese encephalitis and avoid importation during the rainy season. Foals born to imported mares also should receive the vaccine.

—Lloyds Equine Disease Quarterly

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