Japanese encephalitis is a virus of the flavivirus family. It is passed by the Culex mosquito. Not only humans are affected by the virus. Mosquitoes can also infect horses and pigs leading to encephalitis in horses and abortion in pigs. Wild birds are probably the natural hosts and mosquitoes are the vectors.    A vector does not cause a disease but passes it on. When mosquitoes infect an animal, the animal can become a carrier of the virus. When other mosquitoes feed on these newly infected animals they take up the virus and can infect other animals or humans. People in rural areas where the virus is common are at highest risk. Japanese encephalitis does not usually happen around is towns and cities. It is more likely to affect children, because adults in areas where it is endemic generally become immune as they get older.  

              A person with Japanese encephalitis will probably have no symptoms, they will appear 5 to 15 days after being affected.A person with a mild infection may have only a fever and a headache, but in severe cases, symptoms can develop quickly. There may be a headache, high fever, tremors, nausea, vomiting, stiff neck, and spastic paralysis. Signs of altered mental status includes stupor, disorientation, and coma. Children may have convulsions. There may be swelling of the testicles. If the brain is involved, life-long neurological  defects can result, such as deafness, uncontrollable emotions, and weakness on one side of the body. The chance of survival varies, but children are most at risk.

           Mosquitoes become infected by feeding on wild birds and domestic pigs that have been infected with the virus to humans and animals.Birds and other animals cannot transmit the infection to human. Only infected mosquitoes can pass it on. The mosquitoes mainly live in agricultural and rural areas. Their larvae breed in pools of water, for example, flooded rice fields.

            Once a person has the disease, treatment can only relieve the symptoms. Antibiotics are not effective  against virus, and no effective anti-viral drugs have been discovered. Vaccination is recommended. People who spend time outdoors in rural areas should use protective clothing, bed nets, and repellents, and they should sleep in air-conditioned well-screened rooms.