Chicken flu is tracked to humans Southern China is ground zero for dangerous new virus


HONG KONG -- A yellow sign stenciled with interlocking black rings and a single word hangs over Kennedy F. Shortridge's laboratory. That word is "Biohazard."

"In here," Shortridge said, opening the chrome door of an incubator, "we will grow the virus."

Dozens of scientists around the world, principally in Hong Kong and at the Centers for Disease Control and Prevention in Atlanta, are working feverishly to understand the new flu virus that has spread from chickens to humans here, so far killing two.

The flu, called H5N1, is a previously unknown strain of influenza virus that has jumped directly from chickens to humans, a leap that apparently had not occurred in previous flu outbreaks.

For Shortridge the emergence of a new influenza virus, while not necessarily this one, seemed inevitable, given both ancient agricultural practices in China and the current system of farming in Guangdong province, the source of much of Hong Kong's food.

A microbiologist at the University of Hong Kong, Shortridge has spent much of his two-decade career here examining the ecology of flu viruses in southern China -- where they come from, what their hosts are, how they mutate, how they are transmitted.

"China is the principal reservoir for influenza," he said, "and southern China is the epicenter."

China's role as an incubator of influenza viruses can be traced to the domestication of the duck, about 2,500 B.C., near the beginning of Chinese recorded history.

"Studies suggest that aquatic birds -- ducks -- are the principal hosts for influenza in nature," Shortridge said. The two main habitats of these ducks were on lakes in the far reaches of Siberia and in the rice paddies of southern China.

Migrating ducks, which were hosts to great numbers of flu viruses, "seeded" southern China with the viruses as they moved south, and the virus took hold in domesticated ducks.

In the early years of the Qing dynasty, in the mid-17th century, Chinese peasants began keeping ducks in rice paddies.

"Ducks were used as an adjunct to rice farming," Shortridge said. "Ducks ate insects and crabs, but didn't eat the rice grains. You develop a perfect ecological system."

And because in most southern Chinese villages, ducks and chickens and pigs and people all live in close contact, often with the animals next to or even in houses, influenza viruses moved into pigs and then to humans. Pigs, Short-ridge said, have been the "mixing vessels" in which the avian flu virus is genetically rearranged so that it can infect humans.

But even with this broad understanding, Shortridge said, the sudden appearance of H5N1 and its apparent direct transmission from chickens to humans raises a welter of questions.

"The important question to me is: How is the virus getting across from birds to humans?" said Shortridge, a lanky Australian. "The second important question is: Will this virus undergo any transformation that will allow it to infect humans and cause an epidemic or a pandemic?"

Already, tens of thousands of chickens have died of the virus. And of the eight known and two suspected cases of humans with the H5N1 flu here, direct contact with chickens is the closest health authorities have gotten to establishing a path of transmission.

Blood and respiratory swab samples from chickens as well as human patients and those they have been in contact with are now being analyzed by the CDC in Atlanta. As yet, there are no answers on how the flu is spread.

Pub Date: 12/21/97

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