Key points
- Japanese encephalitis is caused by a virus primarily spread to people through the bite of an infected mosquito.
- Japanese encephalitis virus is maintained in the environment between mosquitoes and other animals like wading birds and pigs.
- People do not spread the virus other than rarely through blood transfusions and possibly organ transplants.
Primary cause
Japanese encephalitis is caused by a virus that is found in Asia and parts of the western Pacific.
About the virus
Japanese encephalitis virus is a member of the family Flaviviridae, genus Orthoflavivirus. Other medically important flaviviruses circulating in the same area include dengue virus in many locations, tick-borne encephalitis virus, Murray Valley encephalitis virus, and West Nile virus in some locations.
Japanese encephalitis virus has a single-stranded, positive-sense RNA genome. The virus particles are spherical and have a diameter of 50 nm.
How it spreads
People become infected with the virus when mosquitoes feed on infected animals and then bite people.
People are considered "dead-end" hosts, meaning they do not develop high enough levels of virus in their bloodstream to spread the virus to uninfected mosquitoes.
The virus does not spread directly from person to person through coughing, sneezing, or touching. However, the virus can spread through blood transfusion or transplanted organs (probable but not confirmed transmission route). Because the virus can be transmitted through blood, people who were recently diagnosed with Japanese encephalitis virus infection should not donate blood and bone marrow for 120 days following infection.
There has been no evidence of spread by:
- Eating infected animals
- Touching or handling live or dead infected animals
However, always follow instructions for fully cooking meat. Always wash your hands after touching animals and avoid bare-handed contact when handling any dead animal. If you are disposing of a dead animal, use gloves or double plastic bags to place the carcass in a garbage can.
Prevent Japanese encephalitis
Transmission cycle
Japanese encephalitis virus is transmitted to humans through the bites of infected Culex species mosquitoes, particularly Culex tritaeniorhynchus.
The virus is maintained in a cycle between mosquitoes and vertebrate hosts, primarily pigs (referred to as amplifying hosts) and wading birds (referred to as natural reservoirs). Although people are dead-end hosts, person-to-person transmission via blood transfusion and probable transmission via organ transplantation has been documented in rare cases.
Japanese encephalitis virus transmission occurs primarily in rural agricultural areas in Asia and parts of the western Pacific, often associated with rice production and flooding irrigation. In some areas of Asia, these conditions can occur near urban centers.
In temperate areas of Asia, Japanese encephalitis virus transmission is seasonal. Human disease usually peaks in the summer and fall. In the subtropics and tropics, transmission can occur year-round, often with a peak during the rainy season.