What is the infectious agent that causes Japanese encephalitis?
Japanese encephalitis is caused by the Japanese encephalitis virus, an arbovirus. Arbovirus is short for arthropod-borne virus. Arboviruses are a large group of viruses that are spread by certain invertebrate animals (arthropods), most commonly blood-sucking insects.
Where is Japanese encephalitis found? 
Japanese encephalitis is found throughout rural areas in Asia. Transmission can also occur near urban areas in some developing Asian countries. It is a seasonal disease that usually occurs in the summer and fall in the temperate regions of China, Japan, and Korea. In other countries, disease patterns vary with rainy seasons and irrigation practices.
How do people get Japanese encephalitis?
The Japanese encephalitis virus has a complex life cycle involving domestic pigs and a specific type of mosquito, Culex tritaeniorhynchus, which lives in rural rice-growing and pig-farming regions. The mosquito breeds in flooded rice fields, marshes, and standing water around planted fields. The virus can infect humans, most domestic animals, birds, bats, snakes, and frogs. After infection, the virus can invade the central nervous system, including the brain and spinal cord.
What are the symptoms of Japanese encephalitis?
Most infected persons develop mild symptoms or no symptoms at all. In people who develop a more severe disease, Japanese encephalitis usually starts as a flu-like illness usually after 6 to 8 days after the bite of an infected mosquito. Symptoms may also include fever, chills, tiredness, headache, nausea, and vomiting. Confusion and agitation can also occur in the early stage. The illness can progress to a serious infection of the brain (encephalitis), and 30-percent of these cases can be fatal. Among the survivors, up to 30-percent will have serious brain damage. JE is positively diagnosed after tests are performed on the blood or spinal fluid.
How common is Japanese encephalitis?
Japanese encephalitis is the leading cause of viral encephalitis in Asia where 30,000 to 50,000 cases are reported each year. The disease is very rare, however, in U.S. travelers to Asia. The chance that a traveler to Asia will get Japanese encephalitis is very small: 1) only certain mosquito species can spread Japanese encephalitis; 2) in areas infested with mosquitoes, only a small portion of the mosquitoes are usually infected with Japanese encephalitis virus; 3) among persons who are infected by a mosquito bite, only 1 in 50 to 1 in 1,000 will develop an illness. As a result, less than 1 case per year is reported in U.S. civilians and military personnel traveling to and living in Asia. Only 5 cases among Americans traveling to or working in Asia were reported from 1981-1992. A sixth case was reported in 2004.
What is the treatment for Japanese encephalitis?
A vaccine is licensed for use in U.S. travelers to rural areas where the disease is common. The vaccine is recommended only for persons who plan to travel in these areas for 4 weeks or more with extensive outdoor activities in rural areas, especially where rice cultivation or pig farming is common, except in special circumstances such as an ongoing outbreak of disease.
Current DoD policy* is to administer the Japanese encephalitis vaccine to personnel who are or who will be stationed in rural areas of Asia in which the disease is endemic and where they have substantial risk of exposure to the virus, especially during prolonged field operations at night. The main groups needing Japanese encephalitis immunization are designated special-operation units, and troops assigned or deploying to Okinawa with extended field exposure. Under normal circumstances, this immunization is not warranted for personnel assigned to or deploying to Korea.
What can I do to reduce my risk of becoming infected with Japanese encephalitis?
AVOID MOSQUITO BITES! Using the DoD Insect Repellent System provides the best protection from mosquito bites. It incorporates permethrin repellent on the uniform; DEET, picaridin, or IR3535® repellent on exposed skin; a properly worn uniform; and sleeping inside a permethrin-treated bed net. Civilian personnel can also purchase or treat clothing with permethrin. Stay in air-conditioned areas or make sure door and window screens are in place and do not have holes. If practical, minimize time spent outdoors during nighttime hours.
Select the image for more information on the DoD Insect Repellent System.
