Nipah virus, RNA virus of the genus Henipavirus, family Paramyxoviridae, that rarely infects humans but can cause deadly encephalitis. In humans, the virus typically incubates for 4 to 14 days before a person develops fever, headache, and other flulike symptoms. In some cases, respiratory illness, including pneumonia and acute respiratory distress, also develops. After 3 to 14 days the patient experiences drowsiness, dizziness, disorientation, mental confusion, and other symptoms of acute encephalitis; in the most severe cases the disease progresses to coma in 1 to 2 days. Depending on the outbreak, 40% to 75% of the persons known to be infected have died; some people who are infected, however, never show any significant symptoms. Patients are given supportive care; there is no treatment or vaccine for the virus. Some survivors of the disease may experience long-term neurological effects, including seizures and personality changes.
Carried by flying foxes (fruit bats) of the family Pteropodidae, especially those of the genus Pteropus, Nipah virus is known to infect both pigs and humans. The virus is typically transmitted to humans from something contaminated by the saliva, urine, or feces of flying foxes, or from contact with the secretions or excretions of an infected pig or human.
A relatively recently identified disease, Nipah virus infection was first diagnosed in 1999 in Malaysia, where pigs developed sometimes severe, transmissible respiratory infections when fruit trees, which attracted flying foxes, were planted among the pens on large pig farms; the virus then spread to other pigs and humans. Subsequent outbreaks have occurred in Bangladesh and India. Nipah virus is closely related to Hendra virus, which is also acquired from flying foxes and causes acute respiratory infections and encephalitis in horses and humans. Hendra virus disease, which typically has a mortality of greater than 50%, has only been reported in Australia.
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