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Japanese encephalitis
Infection
Mosquitoes transmit the infection. The virus is found naturally in pigs and the mosquitoes often breeds in rice fields, which makes JE an infection seen especially in rural areas.

Vaccination
A new vaccine Ixiaro (SBL Vaccines) has been introduced in 2009. The vaccine contains inactivated virus grown in cell culture. The new vaccine should have fever side effects. The protection is 1 year after 2 immunizations, and 2 new immunizations are required after 1 year for continued protection according to the manufacturer.

JE-vaccination is part of the childhood vaccination programme in China, Japan, Taiwan, Thailand and South Korea.

Symptoms
Most infections pass unnoticed. The initial symptoms are headache, reduced consciousness and fever. The infection may be lethal and may cause permanent brain damage.

Diagnosis
Detection of antibodies in a blood sample.

Treatment
Supportive only. No specific antiviral drugs available.

Prevention
Avoid mosquito bites. The mosquitoes, which transmit JE bite primarily during daytime.

More about JE
The WHO estimates that there are at least 50,000 cases per year in Asia and 10,000 deaths. The virus is naturally found in pigs and transmitted to humans by mosquitoes. JE is threfore more prevalent in rural areas.

The distribution can be seend on the map below.

Japane encephalitis appear in small epidemics with years in between. JE is more prevalent during the summer months and in Thailand and Vietnam the infection is five time more prevalent in the local population during May to October compared to the winter months.

JE is extremely rare in visitors and tourists.

A recent study of cases of JE imported to Europe found that the risk of symptomatic JE was 1 per 5 million visitors, and concluded that the risk was so low that routine vaccination of travellers to Southeast Asia was not justified (Hatz et al. J Trav Med 2009;16:200-2003).

A Scandinavian study based on 14 cases registered since 1990 found a risk of approximately 1 per 400.000 visitors (Buhl & Lindquist J Trav Med 2009;16:217-219).

A European consensus group recommend that only visitors to Southeast Asia with prolonged exposure
should be considered for vaccination (Burchard et al. J Trav Med 2009;16:204-16).

Based on these three studies, vaccination against japanese encephalitis should be considered to persons staying for 6 months or more in endemic areas or shorter if visiting areas with a known, on-going outbreak.

Further information: W.H.O. – Japanese encephalitis

Edited 10 November 2009