Japanese Encephalitis

The mosquitoes which carry Japanese Encephalitis virus commonly breed in paddy fields in South-East Asia.

Japanese Encephalitis vaccine is just one of the travel vaccinations we offer at TrExMed Travel Clinic Edinburgh.

Japanese Encephalitis is a potentially serious viral infection, which is endemic in 24 Asian countries. It is mainly transmitted by evening-biting Culex mosquitoes. Although human cases are declining in Japan, South Korea and some parts of China, it is increasingly being reported from Bangladesh, Myanmar, parts of India, Nepal, parts of Pakistan, northern Thailand and Vietnam.

The natural hosts for the virus are water birds, and it is spread to people by mosquito bites. Domestic pigs may also act as an intermediary host and amplify the infection near to people's homes. This may then lead to unpredictable outbreaks of infection, particularly among the younger children who have no immunity.

This is the 'classical' disease pattern of Japanese Encephalitis, and how it typically affects local communities in rural areas, especially near paddy fields in the monsoon season.

The evidence for risk among travellers

Recent evidence, looking at travellers who develop the disease, reveals quite a different risk pattern: There have been at least 21 confirmed cases among visitors to Thailand returning to Western countries reported between 1992 and 2013. Of these, most had only been to Bangkok and/or the tourist islands, 71% had been short-term travellers (4 weeks or less) and a third had been infected in the dry season.

How serious is Japanese Encephalitis disease?

Although most infections go unnoticed, in about one in 250 people, the virus can penetrate through to the brain, causing severe headache, high fever, meningitis and/or encephalitis.

Most such severe cases will require hospitalisation with intensive care. Typically, among young adults a third of cases are fatal, a third go on to have permanent symptoms or signs of neurological damage, and the remaining third make a full recovery. The disease is more serious in the elderly (over 50% case fatality rate).

Japanese Encephalitis prevention

Nicky Armstrong and Jim Bond  April 2017

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