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