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Why is Japanese encephalitis limited to Asia and Oceania?

Consider the current transmission areas of the mosquito below from Valneva, the only seller of Japanese encephalitis vaccine in the U.S.

2023 map from Valneva

Japanese encephalitis is primarily found in Asia because the main vectors of the virus, mosquitoes of the Culex genus, are most common in this region. These mosquitoes breed in rice paddies and other types of standing water, which are abundant in many parts of Asia, particularly in rural areas.

Rice paddies | Steve Douglas

In addition to the presence of the vectors, the disease is maintained through transmission cycles between mosquitoes and amplifying hosts such as pigs and water birds which are also present in Asia. Furthermore, the agro-climatic conditions such as high temperature, heavy rainfall and high humidity that are prevalent in many parts of Asia, are favorable for the development and survival of the mosquitoes, and thus contribute to the maintenance of the transmission cycle.

If you are traveling to one of these areas, you should consult with a travel health specialist about the Japanese encephalitis vaccine.


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