Fatal encephalitis due to Nipah virus among pig-farmers in Malaysia

Background Between February and April, 1999, an outbreak of viral encephali tis occurred among pig-farmers in Malaysia. We report findings for the firs t three patients who died. Methods Samples of tissue were taken at necropsy. Blood and cerebrospinal-f luid (CSF) samples taken before death were cultured for viruses, and tested for antibodies to viruses. Findings The three pig-farmers presented with fever, headache, and altered level of consciousness. Myoclonus was present in two patients. There were s igns of brainstem dysfunction with hypertension and tachycardia. Rapid dete rioration led to irreversible hypotension and death. A virus causing syncyt ial formation of vero cells was cultured from the CSF of two patients after 5 days; the virus stained positively with antibodies against Hendra virus by indirect immunofluorescence, IgM capture ELISA showed that all three pat ients had IgM antibodies in CSF against Hendra viral antigens. Necropsy sho wed widespread microinfarction in the central nervous system and other orga ns resulting from vasculitis-induced thrombosis. There was no clinical evid ence of pulmonary involvement. Inclusion bodies likely to be of viral origi n were noted in neurons near vasculitic blood vessels. Interpretation The causative agent was a previously undescribed paramyxovir us related to the Hendra virus. Close contact with infected pigs may be the source of the viral transmission. Clinically and epidemiologically the inf ection is distinct from infection by the Hendra virus. We propose that this Hendra-like virus was the cause of the outbreak of encephalitis in Malaysi a.