As in Asia, many of those birds are kept in free-range backyard farms as sources of income and food.
The birds live in close proximity to humans and freely interact with wild birds, which can carry the disease.
So far authorities believe that bird flu's human victims have acquired the disease from infected birds, rather than from human-to-human transmission.
If H5N1, or another bird flu strain, acquires the ability to pass easily from person to person, a devastating global pandemic could be imminent, experts warn.
In much of Africa the disease surveillance and monitoring that are key to coping with bird flu are inadequate. Birds often die of poor nutrition and illness, raising the possibility that outbreaks might be missed.
"I hope that this outbreak raises the issue of the benefit of a worldwide surveillance network for emerging disease [in] wildlife so that we can have early warning for H5N1 and other diseases," said Hon Ip, diagnostic virologist at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisconsin.
Economics present another challenge. Many African nations lack the funds to adequately compensate farmers, who may resist the killing of their valuable birds.
Migrating Birds or Humans to Blame?
Bird flu has been spreading steadily westward from its East Asian source. In recent weeks it has been responsible for human deaths in Turkey and Iraq.
Experts aren't certain how the virus reached Africa.
"We don't know how it got there," said Juan Lubroth, a Rome-based senior animal health officer with the UN Food and Agriculture Organization (FAO).
"There may be some points we're missing along the way, where the infection was present and not detected, so we don't have all the dots to connect."
Preliminary genetic sequencing information indicates that the strain is of Asian lineage, similar to that which recently spread into Turkey
Officials were not shocked at the deadly flu's appearance in Africa. In October the FAO announced that the virus would likely reach Africa in the near future, citing migrating birds that would soon be moving from breeding grounds in Asia to their winter habitat in Africa. (Read "Bird Flu's Spread to Africa Could Be Imminent, UN Warns.")
Migrating birds are prime suspects in the African appearance of bird flu, but their role remains uncertain.
If they transmitted the disease, Ip wonders, why weren't outbreaks seen earlier in the season? Why weren't they detected along the migration route such as on Africa's Mediterranean coast?
"Countries in Africa are significant importers of poultry products from Southeast Asia," Ip said.
"Borders are also relatively porous in many areas. There are many possible routes—including other domestic birds at the farm and legal and illegal trade—[by which] the H5N1 virus could have arrived in Jaji [Nigeria] in addition to introduction by wild birds.
"The location of the outbreak is the only argument for migratory birds as the cause of the spread. I would suggest that these other mechanisms are at least as likely."
The FAO's Lubroth agrees that wild birds may not be responsible—or may have been responsible but received significant human help.
"There are other ways diseases move around the world," he said. "It could be that wildlife introduced the virus, but through our own activities of commerce, the disease spread."
Human Pandemic More Likely?
Today the African appearance of H5N1 doesn't appear to have moved the world closer to a human pandemic.
Preliminary genetic work suggests that the African strain has not mutated into a form more lethal to humans than that seen so far in Asia. "At the moment the concern is that here is another example of a long-distance geographical spread," Ip said.
"Whether it is by wild birds or human activity is unclear, but the concern is that the world does not appear to be able to stop the advance of the virus."
Full genetic information about the Nigerian virus strain should be available later in the week, which will allow scientists to compare the strain with those that have caused human infections in other countries.
The data should paint a clearer picture of the current risk to African humans, but Lubroth stresses that even without large-scale human infection, the outbreak is already a disaster.
"We're still talking about people's livelihoods that depend on poultry and also a critical food source," he said. "So for us it's still an emergency. We're in emergency mode."
Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
|
SOURCES AND RELATED WEB SITES
|
