Japanese Encephalitis is most definitely not limited to Japan. But what is it? The CDC defines it as 'a common mosquito-borne viral encephalitis found in Asia.' In English, that basically translates out to a virus that you can catch from being bitten by a mosquito that makes your brain bigger, but in a bad way. It is in the genus Flavivirus, which is further contained in the Flaviviridae family.
Japanese Encephalitis is transmitted via mosquito bite. The variety of mosquito that most frequently carries the virus is called Culex tritaeniorhyncus. It is not possible to infect other people with this virus.
This particular virus is usually relegated to rural portions of Asia; however, there are instances of urban infection. Thus, it is important to take proper precautions by obtaining the vaccine (It is recommended that the last dose is 10 days before travel to endemic regions). Alternatively, for those who cannot have access to the vaccine for whatever reason, wear long-sleeved clothing and apply DEET whenever possible. As the particular mosquito that carries this virus usually comes out between the early evening and morning, avoid being outside during those times. It is to be noted that most travellers who are not going to be in the region for a lengthy stay are not at high risk to become infected.
Most people who are infected do not show any symptoms, or experience very mild symptoms. However, flu-like symptoms are indicative of a more serious case, and can eventually lead to death, paralysis, or other brain damage.
Good luck. If you've progressed to a bad state, the only thing that the good doctors or nurses can do for you is treat the symptoms.