By David Brown
Washington Post Staff Writer
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.
About 80,000 birds died at a large farm in the northern state of Kano in early January. At the time, the deaths were attributed to Newcastle disease and cold cholera, but may have been caused by H5N1 influenza. The first confirmed cases were in Kaduna state, about 100 miles to the south.
In 2002, Nigeria imported 1.2 million chickens, according to statistics on the U.N. Food and Agricultural Organization (FAO) Web site. Nearly all the birds were day-old chicks.
China, Nigeria and the FAO signed a $22.7 million agreement in March 2003 to have 520 Chinese agriculture experts, including poultry technicians, help Nigerian farmers. Nigeria also imported live birds from China until January 2004, when the trade was banned because of bird flu outbreaks in Asia.
Despite the import ban, numerous reports say chickens continue to come in from China. At a news conference last week, Bello said that "birds come every day from China, Turkey . . . so Nigeria is exposed," according to a newspaper report.
In a study published this month in the journal Proceedings of the National Academy of Sciences, an international team led by two Chinese researchers reported that a survey of more than 50,000 birds in live-poultry markets there found 1 percent were infected with H5N1 virus.
The researchers also sampled about 13,000 migratory birds and found that six were carrying H5N1 and did not appear to be ill -- evidence that healthy migrants may be able to carry the microbe long distances.
The genetic diversity in the virus samples from domestic chickens led the researchers to deduce that "H5N1 virus is perpetuated in poultry largely through the movement of poultry and poultry products, rather than by . . . migrating birds."
Although no H5N1 has been found in wild birds in West Africa, elsewhere the virus has been found in three duck species that spend winter in Africa. They are the garganey, the northern pintail and the northern shoveller -- about 3.5 million birds in all -- said Alex Kaat of Wetlands International.
None of the wintering places are close to the chicken outbreaks, however, Kaat said.