Japanese encephalitis is the main cause of viral encephalitis in Asia. It is caused by a flavivirus and is usually associated with shivering, general feeling of malaise, and fever.
Close to 90 percent of infections are asymptomatic. When symptoms of encephalitis (such as fever, shivering, and severe headaches) appear suddenly, they are followed by various neuropsychic problems such as stupor, confusion, and vegetative disorders. The mortality rate among clinical cases is 20 to 50 percent, and 30 percent of those who survive the disease subsequently suffer permanent conditions such as epilepsy, ataxia, or behavioural disorders.
Japanese encephalitis is transmitted by the bite of a mosquito from the Culex species. Humans are accidental hosts for the virus that generally infects domestic pigs, some mammals, and marsh birds. The mosquitoes thrive mostly in rural areas. They usually bite at dawn or dusk. Transmission of the virus to humans is occasional at best: it is believed that only 1 bite out of 2,500 transmits the disease. The incubation period lasts about 1 week and the infection confers long-term immunity on the host.
The usual precautions against mosquitoes should be followed: apply an insect repellent, use bed netting and wear light-coloured long-sleeve shirts and long pants. The risk of contracting Japanese encephalitis is minimal. Since 1981, only 6 cases have been reported among Americans living in endemic regions in Asia.
The vaccine is recommended for travellers 18 years and older that plan to stay in endemic areas for at least 1 month, especially during the rainy season. The vaccine is given in 2 shots (on days 0 and 28). Ten to 20 percent of vaccinated individuals experience side effects such as headaches, myalgia (muscle pain), fever, and general malaise.
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