Bats may spread new Malaysian virus.

A rash of encephalitis cases caused by Nipah virus in Malaysia between September 1998 and June 1999 killed more than a third of the victims, researchers there report.

The newly discovered virus belongs to the paramyxovirus group. Although one person caught the virus from an infected dog, in nearly all cases, the illness spread from pigs to people working on pig farms, says Chong Tin Tan, a neurologist at the University of Malaysia in Kuala Lumpur. Pigs that have the virus die, Tan reports.

Originally, however, the virus may have come from bats, he suggests. A related virus called Hendra is carried by fruit bats, also known as flying foxes. Highway construction in northern Malaysia could have uprooted bats from their native roosts and driven them into close proximity to the pig farms where the Nipah outbreaks occurred, Tan says.

"The high density of pig farms in the epidemic area contributed to the rapid spread of the disease," he says.

The disease causes fever, headache, dizziness, and vomiting, as well as brain inflammation, the hallmark of encephalitis. The illness showed little ability to spread from person to person. Three healthcare workers who hadn't been near pigs tested positive for the virus after treating infected patients, but none came down with the disease.

Tan and his colleagues studied 94 patients, 30 of whom died from the disease. Fifty patients recovered fully, and the others retained at least some brain damage, Tan and his colleagues report in the April 27 NEW ENGLAND JOURNAL OF MEDICINE.

Another hospital in Malaysia reported a 41 percent mortality rate among 103 patients treated, Tan says. In both cases, patients were treated with ribavirin, an antiviral medication.

Last year, physicians at Tan Tock Seng Hospital in Singapore treated Nipah-infected men who worked at a slaughterhouse that had imported Malaysian pigs. Of 11 diagnosed with the virus, 9 developed encephalitis and all survived after treatment with a pair of antivirals, ribavirin and acyclovir.

The mode of Nipah virus transmission remains unknown, but it clearly involves close contact with infected animals, both groups say.