Profile: Emerging diseases discussed at international conference of scientists

03/30/2002
NPR: Weekend All Things Considered
Copyright 2002 National Public Radio, Inc. All Rights Reserved.

JACKI LYDEN, host: The source of emerging diseases is the first line of inquiry for scientists. Diseases have been jumping from animal to animal for centuries. Flu viruses originally came from ducks; AIDS, from monkeys; West Nile disease, from birds. And it's still happening. Scientists gathered this week in Atlanta for an international conference on emerging diseases, and NPR's Richard Knox gathered tales of fruit bats, pigs, turkeys and new human diseases.

RICHARD KNOX reporting:

The newest human disease threat is called Nipah virus. It came out of the Malaysian rain forest. In late 1999, hundreds of people were suddenly struck with fever, severe headaches, labored breathing, coughing fits and aggressive behavior. Forty percent of them died.

Mr. PETER DASZAK (Columbia University): This virus is from fruit bats.

KNOX: Peter Daszak of Columbia University tries to understand where diseases come from. He says Nipah virus has a lot to tell us.

Mr. DASZAK: It emerged through pigs, which are found pretty intensively in Malaysia, and these act as amplifies-host(ph) to increase the amount of virus in the atmosphere as they cough it out into the environment, and then infect humans.

KNOX: But how did Nipah virus get from fruit bats to pigs? Daszak thinks the story starts with slash-and-burn clearing of the Indonesian rain forest. That's nothing knew, but when El Nino weather patterns made for an unusually dry rainy season, forest fires raged out of control, and that produced heavy smoke over the entire region, the first link in the Nipah virus chain of events.

Mr. DASZAK: Deforestation caused a large haze event, which then dropped the fruit production of forest trees and caused fruit bats to migrate closer to piggeries.

KNOX: That's because pig farmers maintain stands of oil palms and other fruit-bearing trees. The trees attract the starving bats to the farms.

Mr. DASZAK: Where they're able to infect pigs and then humans with this new virus. At least that's one hypothesis.

KNOX: Nipah virus is only the latest chapter in a long history. Of 1,500 known human diseases, about 40 percent are what scientists call zoonotic--that is, they can be transmitted from animals to humans or vice versa. But nearly three in four newly emerging diseases came from animals. Daszak thinks this is because of human intervention--everything from pig farming to air travel.

Mr. DASZAK: We change the habitat. We cause environmental changes to the habitat that allow certain strains or certain types of pathogens to jump host, to expand in range, to increase their population. There's just an ability for these strains to adapt to any of our changed environments that we put across to them, and that's how diseases emerge essentially.

KNOX: And it's not just the exotic bugs. Scientists have discovered that one of the most common human diseases came from turkeys. It's a virus that turns out to be a leading cause of pneumonia. Albert Osterhaus at the University of Rotterdam went looking for it after a colleague complained half his cases of childhood pneumonia had unknown causes. Eventually, Osterhaus found the cause. At a scientific session in Atlanta, he said that it's genetically very close to a turkey virus.

Mr. ALBERT OSTERHAUS (University of Rotterdam): The obvious question there was are we dealing with a zoonotic virus, a virus that's being transmitted from turkeys to humans--that's the obvious thing we thought.

KNOX: Obvious but wrong. The new virus, called human metapneumo virus, is turning up everywhere--in Holland, England, Australia, Canada. And not only among children. It causes serious disease in elderly people and those with low immunity. Dr. Dean Erdman of the Centers for Disease Control and Prevention says nearly everyone has been infected.

Dr. DEAN ERDMAN (Centers for Disease Control and Prevention): Virtually all kids have antibody by an early age, so that means that the virus isn't entering the human population sporadically. It's being spread from person to person.

KNOX: Another twist: the new pneumonia virus is a cousin of the Nipah virus of Malaysia. Fortunately the more lethal Nipah virus can't be passed from person to person, so Daszak says there's no immediate reason to worry that Nipah might find its way here.

Mr. DASZAK: We're not concerned that it's going to emerge in the States by some imports of fruit bats or something. What it warns us about are diseases that are out there that are unknown to us, that if we change the environment we give them a chance to emerge into human populations.

KNOX: Humans are not about to stop changing the environment, so infectious disease specialists expect more nasty surprises. Richard Knox, NPR News, Atlanta.