Nipah virus encephalitis overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Nipah virus was identified in 1999 when it caused an outbreak of neurological and respiratory disease on pig farms in peninsular Malaysia, resulting in 105 human deaths and the culling of one million pigs. In Singapore, 11 cases including one death occurred in abattoir workers exposed to pigs imported from the affected Malaysian farms. The Nipah virus has been classified by the CDC as a Category C agent (http://www.bt.cdc.gov/agent/agentlist-category.asp).
Symptoms of infection from the Malaysian outbreak were primarily encephalitic in humans and respiratory in pigs. Later outbreaks have caused respiratory illness in humans, increasing the likelihood of human-to-human transmission and indicating the existence of more dangerous strains of the virus.
Based on seroprevalence data and virus isolations, the primary reservoir for Nipah virus was identified as Pteropid fruit bats including Pteropus vampyrus (Malayan flying fox) and Pteropus hypomelanus (Island flying fox), both of which occur in Malaysia.
The transmission of Nipah virus from flying foxes to pigs is thought to be due to an increasing overlap between bat habitats and piggeries in peninsular Malaysia. At the index farm, fruit orchards were in close proximity to the piggery, allowing the spillage of urine, faeces and partially eaten fruit onto the pigs. Retrospective studies demonstrate that viral spillover into pigs may have been occurring in Malaysia since 1996 without detection. During 1998, viral spread was aided by the transfer of infected pigs to other farms where new outbreaks occurred.