Poultry, Not Wild Birds, Most Often Carries Deadly Avian Flu to Africa
Thursday, February 16, 2006
The lethal strain of H5N1 bird flu found in Nigeria this month probably got there in poultry and not through the movement of wild birds, according to migratory-bird experts and several lines of circumstantial evidence.
The first Nigerian cases were found at a commercial farm with 46,000 chickens, not among backyard flocks that would have greater contact with wild birds. Nigeria imports more than a million chicks a year from countries that include Turkey, where H5N1 appeared last fall, and China, where it has circulated for a decade.
Furthermore, the infected flocks in two of Nigeria's northern states are not near wetlands where migratory birds spend the winter. There are no reports of waterfowl die-offs like those in Asia and Eastern Europe. The few wild species known to occasionally harbor H5N1 arrived months ago and are about to leave.
If it turns out that trade, not nature, was responsible for introducing H5N1 to Africa, better control of trade in domesticated birds may be able to limit the virus's spread there and on other continents, public health experts said.
"If you put all the possible factors in perspective, we wouldn't jump to the conclusion as others do that it was wild birds that brought it," said Ward Hagemeijer, an ornithologist at Wetlands International, a Dutch conservation organization.
William B. Karesh, a veterinarian with the Wildlife Conservation Society in New York, said: "I would never rule out wild birds. But I think we have to look at the most probable routes, and the most probable route would be poultry. How did it skip the whole Nile Delta and get to Nigeria? That kind of bothers me. Common sense would dictate that it should be all over Egypt by now."
The spread of H5N1 by wild birds "is a horrible assumption that a lot of people are making," agreed Peter Marra, an ecologist with the Smithsonian Institution's Migratory Bird Center at the National Zoo. "There is no question that migratory birds are playing a role, but they are not the main players."
Marra said more attention should be given to the legal -- and illegal -- movement of poultry and pet-trade birds because "that is where you can actually do something about it."
Some of this reasoning appears to have support in Nigeria, as well.
The Guardian, a daily newspaper published in Lagos, recently quoted the country's agriculture minister, Adamu Bello, as saying, "We think someone may have imported or smuggled in contaminated birds."
Epidemiological teams of local and foreign scientists are investigating the outbreak of H5N1 in Nigerian poultry and sampling wild birds for the virus.
About 60 percent of the country's poultry production is in backyard flocks, 25 percent in large commercial farms, and the rest in mixed operations.