Scientists have unmasked a killer responsible for the deaths of at least 95 people in Malaysia in the last 6 months, most of them pig farm workers. The culprit, named the Nipah virus for the small town from whence the strain was first identified, is a previously unknown virus that replicates in pigs and seems to be easily transmitted to humans. It is closely related to another notorious agent, the Hendra virus, which surfaced in Australia in 1994. But the new virus spreads much more rapidly, making it an emerging virus of grave concern, researchers say.