Deadly New Virus Draws Experts to "Hot Zones"
Bijal P. Trivedi
National Geographic Today
|January 21, 2003|
This summer, a team of virus hunters will journey to Australia,
Malaysia, India, Sumatra and Thailand to explore what they call "hot
zones"sites where deadly new diseases have emerged.
In all the locations the common enemy is the Nipah virus, or a relative. The Nipah broke out in Malaysia in 1998. Now known to be transmitted by a fruit bat, it first killed thousands of pigs. Within weeks, it spread to people. The final human death toll was more than 110.
Now the virus hunters are on the move to learn why and how the Nipah virus strikes. Their research can help head off not only the Nipah but also other virulent diseases that break out suddenly to plague man and beast.
To curtail the initial Nipah outbreak, the Malaysian government slaughtered 1 million pigsdecimating the local swine industry.
"We want to know what changes drove this virus to emerge in the first place," says Peter Daszak, executive director of the Consortium for Conservation Medicine, a research group that focuses on emerging diseases, based at Wildlife Trust in Palisades, New York. "What conditions allowed this virus to jump from bats to pigs to people?"
The summer's investigations take on a new urgency because of recent reports that the Nipah virus, and other similar ones, may be more widespread in Southeast Asia than anybody recognized.
A Quick Killer
The National Institute of Health has awarded $1.4 million to the Consortium to fund further research on the Nipah virus and the related Hendra virus, also carried by fruit bats.
Fruit bats range from Southeast Asia all the way to Africa, raising concerns that different species may harbor more dangerous variants of the Nipah. "There are probably related viruses all over the area with the potential not just to cause outbreaks in agricultural stock but also to cause serious disease in humans," says Stephen Morse, a viral epidemiologist at Columbia University in New York, director of Columbia's Center for Public Health Preparedness and author of the book "Emerging Viruses."
In Malaysia, Nipah's host, or "reservoir," is a large fruit bat, Pteropus vampyrus, with a body the size of a small puppy and a 5-foot wingspan.
Hume Field, a wildlife veterinarian at the Queensland Department of Primary Industries, in Brisbane, Australia, who was in Malaysia in 1999 during the outbreak, helped determine that local fruit bats carried the disease.
Field and another colleague netted more than 300 bats and sent blood samples to labs in Australiathey tested positive.
Nipah replicates fast in pigs. Passage to the lungs brings on a "terrible rasping cough," hemorrhaging and raging pneumonia, Field says. When the virus hits the brain, it kills quickly.
Environmental Change, Reservoirs of Disease
Humans get the virus from contact with the infected pigs. Flu-like symptoms can lead to encephalitis and catatonia. In 40 percent of cases the disease is fatal.
Nipah's emergence in 1998 may have derived from the interaction of man and nature, according to Daszak and researcher Jonathan Patz, director of the Program on Health Effects Of Global Environmental Change at Johns Hopkins University in Baltimore.
The researchers envisioned a scenario where an El Niño caused severe dry conditions. Fires that people had set to clear land burned out of control.
The smoke and haze stunted fruit development in the shrinking forests and forced the bats to migrate to places outside their usual habitatlike the forest outskirts, near neighboring pig farms.
On many farms, animal pens mingle with orchards. The researchers believe that fruit bats may have contaminated fruit that then fell into the pigpens.
"It's a really unnatural set of circumstances that has brought pigs in close contact with fruit bats," says Daszak. "The real tragedy is that Pteropus vampyrus is already endangered. Now these viruses make it even more unwanted."
"It's an extremely complex situation," says Patz. "These environmental landscape changes like logging and burning are global in scale, and have the potential to bring together people, wildlife and reservoirs of diseases in ways we couldn't anticipate."
Researchers understand little about the link between ecological disruption and disease. The field requires a multidisciplinary approach. The Consortium, for example, draws on information from ecologists, epidemiologists, physicians, public-health specialists, veterinarians, virologists and wildlife specialists.
"With increasing globalization there are more opportunities to spread an otherwise geographically contained disease," Morse says. "A good surveillance system is required to prevent such outbreaks."
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