|Wild birds are the ultimate
source of all avian flu’s - but that,
scientists argue, does not mean that they
are important in spreading the current virus
or should be wiped out to stop it.
Scientists searching for the roots of the A(H5N1) virus that is threatening to turn into a human pandemic consider live bird markets, traveling poultry workers and the movement of domestic poultry and fighting cocks more likely vectors for spreading the disease from country to country and from farm to farm.
Wherever the strain originated, it has been surviving and mutating in domestic flocks for years, scientists said.
By DONALD G. McNEIL Jr. in the New York Times (Volkskrant 16-10-2004)
Migrating birds are the source of all bird
flu’s but are not known to be spreading
the new, virulent strain Scientists believe
close-packed birds in markets and on farms
and fighting cocks are bigger problems.
|The issue became important early
this year, when some Asian health officials
accused migratory birds of spreading the flu
and threatened to attack them with the same
lethal vigor that has been applied to domestic
chickens. For a brief period in July, Thai
officials killed open-billed storks and chopped
down the trees they nested in. Singapore officials
publicly - and rather fantastically- discussed
killing crows and mynahs, which do not migrate,
and netting wild birds to clip their wings.
The gates of nature reserves in several countries were closed and people were warned to shun wild birds. In Vietnam, panic led to the release of many pets, which were seen roosting in city trees.
"I've never seen anything like it," said Colin Poole, Asia director for the Wildlife Conservation Society, which runs the Bronx Zoo in New York and animal protection programs around the globe. "Birds had become the enemy."
In fact, scientists said, most ways the flu can move depend on humans. In "wet markets," dozens of birds are penned together. Poultry workers' boots and truck tires can track infected feces long distances.
Fighting roosters are frequently carried long distances to bouts where thousands of dollars may be bet on them. When restrictions are imposed, they have been smuggled, even crossing borders hidden in hubcaps of cars, one doctor said.
"We don't have indications that wildlife are major players" in the current outbreak, said Dr. Juan Lubroth, senior officer of the infectious disease group at the Food and Agriculture Organization of the United Nations.
The genes of all strains of avian flus can be found in wild waterbirds. In the Arctic, where many spend their summers, viruses "get mixed up in the ponds like soup, and survive even when they freeze," said Dr. William Karesh, director of field veterinarians for the Wildlife Conservation Society. "The mixing and matching has been going on for thousands of years."
Theoretically, they could be vectors for spreading the disease to new continents, because Asian and American birds share pools in Siberia and Alaska and sometimes switch flyways, said Dr. Richard Veit, an ornithologist at the College of Staten Island. Pintail ducks banded in Asia have been shot in North America and vice versa, he said. Some shorebirds, like sanderlings, migrate as far as New Zealand and Chile.
That, however, is not considered a likely transmission route.
If a very lethal strain emerged in the Arctic, it would probably die out there. "Dead birds don't fly far," said Dr. Carol Cardona, a poultry veterinarian at the University of California at Davis.
Wild birds have sometimes been unfairly blamed. Poultry farmers singled out cattle egrets for a California flu outbreak, "but the egrets were negative - it was the egg flats being trucked from farm to farm without being cleaned," Dr. Cardona noted.
Although Asian newspapers have quoted government officials saying that thousands of wild birds would be tested, few results have been released, Mr. Poole said. A friend in the Thai government, he said, told him the storks killed there were negative.
Mr. Poole said he could find only seven birds of six species that were confirmed positive for the A (H5N1) strain, all in Hong Kong: a black headed gull, two gray herons, a little egret, a peregrine falcon, a pigeon and a tree sparrow. The last three were found dead near infected farms.
"Let's speak in the singular," he said. "That is a dead migratory bird: the gull."
(Some falcons also migrate, but not with the regularity that shorebirds do.)
"The evidence I can find," Mr. Poole concluded, "is that migratory birds are not vectors, but victims."
Both he and Dr. Lubroth, speaking at a conference at Rockefeller University in New York on animal-human diseases, showed that outbreaks had not followed flyways or migration schedules.
"There are no waterfowl that winter in southern China and then go to Vietnam, Cambodia, Indonesia or central Thailand," said Mr. Poole, who lives in Cambodia.
Dr. Lubroth showed that outbreaks appeared in areas with the largest concentrations of domestic chickens, pigs and people. (Asia has seven billion chickens, he said.)
Vaccination is illegal in countries like Thailand that export many chickens because Europe and the United States forbid imports from countries that vaccinate. But China and Indonesia consume most of their own poultry and allow inoculation. an epidemic, said Koh Kheng Lian, a professor of environmental law at the University of Singapore.
Besides upsetting ecosystems, it can have unintended consequences. In the 1950's, she said, Mao urged peasants to kill wild birds that were eating rice crops. The result was disastrous because the birds also had kept rice-eating worms in check.
Dr. Lubroth said farms should adopt biosecurity measures like quarantining newly purchased birds until they prove healthy, netting farm ponds to keep wild birds away, and washing all boots and tires.
Bird handlers have some dangerous habits. For example, cock handlers suck blood and mucus from beaks during fights. And Buddhists hold birds to their faces in prayer before releasing them.
"If you were thinking of a risk to human health, this is it," Mr. Poole said. "But as a religious issue, it would be hard to stop. The king does it every week."