Nipah virus encephalitis.

Nipah virus was first discovered in 1999, after a severe outbreak of viral encephalitis among pig farm workers in Malaysia. The disease is thought to spread from Pteropus bats to pigs and then to humans following close contact. The reported mortality rate in this outbreak was 40%. The main necropsy finding in patients with Nipah virus encephalitis was disseminated microinfarction associated with vasculitis and direct neuronal involvement. Relapse of encephalitis was seen in 10% of those who survived the initial illness. Since that initial report, recurrent outbreaks of Nipah virus encephalitis have been seen in Bangladesh and West Bengal, India. These outbreaks occurred between January and May, with Pteropus giganteus as a reservoir of the virus. In Bangladesh, the virus probably spread directly from bats to humans-with human to human spread as another important mode of infection-and the mortality rate was 70%.