Japanese Encephalitis

Japanese Encephalitis (JE) is a viral infection of the brain caused by the Japanese Encephalitis virus, a member of the Flavivirus family. It is transmitted to humans through the bite of infected Culex mosquitoes, which are most active during the evening and at night. The virus circulates primarily among pigs and wading birds, with humans being incidental hosts. Japanese Encephalitis is found across a wide area of Asia and the western Pacific, with the highest risk in rural and agricultural settings, particularly in rice-growing regions where mosquito populations thrive. Countries including India, Nepal, China, Thailand, Vietnam, Indonesia, and the Philippines all have areas where the disease is present. The transmission season varies by region but is often associated with the monsoon and post-monsoon period. While the overall risk to travellers is relatively low, those spending prolonged periods in rural areas, undertaking outdoor activities at dusk or dawn, or travelling during peak transmission season face a considerably higher risk of exposure.

Symptoms

The vast majority of people infected with Japanese Encephalitis virus, around 99 percent, will experience no symptoms or only a mild febrile illness. However, in the small proportion of cases where the virus crosses into the brain and causes encephalitis, the consequences can be severe. Symptoms of encephalitis typically develop five to fifteen days after infection and begin with a sudden high fever, headache, vomiting, and general malaise. As the condition progresses, neurological symptoms may develop, including neck stiffness, confusion, disorientation, tremors, seizures, and in serious cases, coma. Approximately one in four people who develop encephalitis will die from the disease, and up to half of survivors are left with permanent neurological damage, including memory problems, behavioural changes, weakness, or paralysis. There is no specific antiviral treatment for Japanese Encephalitis, meaning medical care focuses on managing symptoms and supporting recovery. Given the severity of outcomes in those who develop encephalitis, vaccination is strongly recommended for at-risk travellers.

Vaccination

The Japanese Encephalitis vaccine available in the UK is Ixiaro, an inactivated vaccine that is safe, well tolerated, and highly effective. The primary course consists of two doses given twenty-eight days apart, with the second dose completed at least one week before potential exposure to the virus. A booster dose is recommended twelve to twenty-four months after the primary course for those who remain at ongoing risk. The vaccine is recommended for travellers spending a month or more in endemic areas, those undertaking frequent trips to affected regions, and anyone whose itinerary involves significant time outdoors in rural or agricultural settings during peak transmission season, even on shorter trips. Mosquito bite avoidance measures, such as using insect repellent and wearing long-sleeved clothing in the evenings, remain important even for vaccinated travellers. At Market Harborough Travel Clinic, we will carefully assess your itinerary, activities, and length of stay to determine whether the Japanese Encephalitis vaccine is recommended for your trip.

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