An increase in cases of acute febrile encephalitis occurred in Western Malaysia between September 1998 and May 1999, and a similar illness was reported in Singapore in March 1999. Most cases occurred in males who had been exposed to pigs, or among abattoir workers, and at least 100 deaths were reported. The illness was characterized by fever and headache, followed by drowsiness and disorientation; patients with severe cases developed seizures and coma within 24 to 48 hours. Concurrently, there were also illnesses and deaths among pigs in the same region, although the symptoms predominantly involved the respiratory system, and only a few pigs had signs of neurologic disease. From a cerebral spinal fluid specimen from a human patient, Dr. Chua and colleagues were successful in isolating a virus that was morphologically identified as belonging to the family Paramyxoviridae, and is now known as Nipah virus.