CDC Traces Source

ATLANTA - In a quarantined laboratory, U.S. scientists outfitted in plastic biohazard spacesuits and breathing through air tubes are probing a killer that has struck on the other side of the world.

The mysterious microscopic enemy has killed more than 100 people in Malaysia in seven months, and scientists are baffled about its origin and mode of transmission.

"Every couple of years something like this comes along," says Dr. C.J. Peters, head of the special pathogens branch at the Centers for Disease Control and Prevention. "We don't know how this stuff spreads, how far it's going to go. We really don't know what's at the end of the tunnel."

The rare form of viral encephalitis, which spread from pigs to humans, first surfaced last year near the northern city of Ipoh. It has since sickened more than 250 Malaysians, mostly pig farmers. Many of their herds also fell ill, and some pigs died. A similar illness afflicted 11 slaughterhouse workers in Singapore, one fatally, who butchered pigs imported from Malaysia .

Soldiers have killed almost 1 million pigs and some stray dogs to try to curb the virus . On Monday, pet owners in Malaysia's high-risk areas were told to get their animals checked immediately after new tests confirmed house pets could transmit the disease to humans.

Medical authorities named the new virus Nipah, after the village where it was first isolated.

As remote as the Nipah virus may seem, controlling and understanding it are a concern of epidemiologists around the globe because of fear it could spread quickly.

"In today's world, it's not unrealistic to think of the possibility that someone could get on a plane and land in San Francisco with it," says Dr. Duane Gubler, director of the CDC's Division of Vector-Borne Infectious Diseases at Fort Collins, Colo.

For months, Malaysian health officials were certain the killer was Japanese encephalitis, a mosquito-borne virus common to the area. The two pathogens cause similar symptoms - high fever, aches, eventual coma and, often, death.

But most people in the region had been vaccinated for JE as children. Additionally, it doesn't usually kill adult pigs.

The government declared a state of emergency in three Malaysian states and launched fogging and vaccination campaigns, to no avail. The Nipah virus raged on. And despite no proof that Nipah can infect people who eat or handle pork, the epidemic has wreaked havoc on Malaysia's nearly $400 million pork industry.

On March 7, baffled Malaysian researchers sought help from their counterparts at Gubler's CDC office in Fort Collins.

"It was quite fortuitous that when I sent him an offer to help, he was in the process of sending a note to the CDC asking for help," Gubler says.

The following Saturday morning, a Malaysian researcher arrived in Fort Collins with slides of cells infected with the mysterious virus . The researchers worked through the weekend, screening the sample against dozens of known viruses. All were negative.

When they tried to isolate Nipah, it formed giant cells with multiple nuclei - epidemiological patterns not at all like JE. By Sunday, a red flag had gone up: The Nipah virus fit in none of the three virus families studied at Fort Collins and was actually a previously unknown paramyxovirus. This family includes measles and mumps, but one of the last new paramyxoviruses discovered was the especially virulent Hendra virus .

"That was when we packed it up and sent it to Atlanta," Gubler says.

The samples were taken to the CDC's Level 4 biocontainment lab, which houses deadly microbes that have no vaccine or cure, such as the Ebola virus that killed 245 Zaireans in 1995.

The CDC's medical detectives quickly identified the culprit as related to but far deadlier than the very rare Hendra virus . Hendra was first detected in 1994 in Australia, where it killed 15 racehorses and two trainers.

But they know little else.

"That indicated right away that this was something big. We knew it was a new virus and we knew it was related to a virus that kills people," Peters says. "We're not talking about an outbreak of colds that's going to run through and everybody's going to get over it."

In late March, a team of eight CDC epidemiologists and two Australian researchers packed questionnaires, protective gear, needles and vials and headed for Malaysia .

Wearing gloves, rubber coveralls, boots and battery-operated respirators, the disease detectives began combing through animal feed and trapping rodents. They have spent weeks tramping through pig pens and farming villages in the worst-hit areas. They are interviewing victims and their families and friends: What did they eat? What did they drink? Where did they go? What did they do? It's all to form a hypothesis about how the virus is transmitted.

Blood samples have been taken from birds, turkeys, goats, horses, cattle and wild animals. With the Hendra virus , the culprits were fruit bats.

"We have no idea what the natural reservoir of this virus is," Gubler says.

The CDC's next step is to try to develop a genetically engineered vaccine using mice, rats and guinea pigs.

But Peters hopes the vaccine isn't needed. Killing hundreds of thousands of pigs seems to have helped - as of last week, the number of new cases appeared to be declining, and the disease may ease naturally.

"If we're lucky," Peters says, "in two or three months the outbreak will come under control and we'll never have to make a vaccine."