China’s migrating fowl complicate
efforts to control bird flu
By Elaine Kurtenbach , Associated Press Writer
POYANG LAKE, China—From atop a centuries-old dike, high above the mud flats of China’s biggest lake, the view is one of utter tranquility. A heron drifts by. Warblers dart through bushes.
White-fronted geese splash and dive in ponds.
This wetland, hanging like a pouch from the Yangtze River’s middle reaches, is one of Asia’s most important habitats for migrating birds. But it’s also lined with water buffalo pasture, duck farms and waist-deep ponds and canals where people fish with nets.
This cheek-by-jowl life around the 4,000-square-kilometer (1,600-square-mile) lake illustrates how difficult it can be to keep wild birds, people and domestic poultry from mixing and spreading infectious diseases like bird flu.
The role wildfowl have played in the current outbreak of bird flu remains a mystery. Some experts believe migratory birds may be the source of the deadly strain of avian flu that has jumped to humans this year, killing 23 people in Thailand and Vietnam and the precautionary slaughter of millions of fowl in 10 Asian countries.
Others contend the few wild birds known to have gotten the virus were likely victims of diseased domestic poultry.
“There are certainly other causes for spreading the disease, such as the trade and sales of live birds, day-old chicks and eggs,” said Jeff Gilbert, a zoologist with the World Health Organization in Beijing. “Do not assume in every case that it’s wild birds.”
Still, with experts warning that flu outbreaks could spark a global pandemic, officials in the region are adopting a safe-not-sorry approach and trying to prevent further outbreaks.
“We’re keeping a close watch on waterfowl in southern China, since the climate is wet and warm there and the virus can spread easily,” said Wei Rong, an official at the government headquarters for preventing bird flu.
Teams of researchers from the government-run Chinese Academy of Sciences are in the field hunting for the source of this year’s outbreak and for ways to limit the future risk from migratory birds.
In Japan, experts began investigating after several crows were found infected with bird flu. They fear the birds—aggressive, garbage-devouring pests in urban and rural areas—could somehow pass the virus to humans.
“This is a major problem,” said Hiroyuki Higuchi, a professor at Tokyo University.
Japan has also sent researchers to South Korea to discuss concerns over migratory birds.
“All over the world, they’re loaded with viruses,” said Graeme Laver, an Australian flu expert who has found influenza in many bird species, even on isolated islands of the Great Barrier Reef. “The only thing we can do is to recommend keeping poultry away from wild birds. But that’s very difficult.”
Keeping wild and domestic birds apart is a daunting prospect in China, where the watery southern landscape is ideally suited for raising flocks of ducks and geese.
Traveling along migration corridors stretching from Siberia to New Zealand, wild birds sometimes contract mild cases of bird flu and carry the virus long distances.
Their droppings spread the germs into waterways used by domestic fowl, or dry up and drift through the air breathed by the free-ranging chickens that account for two-thirds of all poultry in China.
In February, authorities banned bird watching and photography in Poyang’s nature reserves. But those restrictions apply only to the lake’s formally designated conservation reserves.
So far, no cases of bird flu have been reported among wild birds around the lake, although some were confirmed on farms near the provincial capital of Nanchang, just an hour’s drive south.
Dry weather may have helped. The lake is at its lowest in two decades, so many migrating fowl have stayed far from farms—well within the vast mud flats that rim the lake, filling only during the flood season.
High dikes protect lowland farms from flooding.
In rural China, farmers often live in close quarters with pigs and poultry, an arrangement experts say is ideal for nurturing infectious diseases, particularly the flu. Last year’s outbreak of SARS, severe acute respiratory syndrome, has also been linked to wild animals.
Bird flu was first identified in Italy about 130 years ago. The first known cases of it jumping directly to humans were in 1997 in Hong Kong, when a strain similar to that found in the current outbreak killed six people. The territory ended that outbreak by slaughtering all its poultry.
Most avian flu outbreaks are short-lived and sporadic, and few of the viruses seem to have mutated into forms deadly to humans. In recent years, though, the number of cases has soared as poultry flocks have expanded and trade in grown birds, chicks and eggs has boomed.
Allowed to spread among domestic poultry, mild bird flu strains have mutated into killer varieties that can wipe out entire commercial flocks—and even wildfowl.
During this year’s outbreak, bird flu killed black swans in southern China. In Hong Kong, a falcon was discovered to have died of the disease. Thai officials say some migratory birds found dead in the country carried the avian virus.
“This virus is especially vicious. It’s killing wild birds that normally wouldn’t get sick,” said Laver.
Martin Williams, a writer and bird watcher based in Hong Kong, contends the spread of avian flu this winter does not match migration patterns—another factor that implicates poultry farming.
While wild birds may harbor the flu, they can also provide clues to its prevention. In a discovery Laver calls “sheer luck,” his research identified a “neuraminidase,” or viral protein, in influenza germs taken from a noddy tern caught on the Great Barrier Reef.
Crystals sent into space and cultivated from that protein were used to develop the antiinfluenza drug Tamiflu, one of humankind’s few defenses against the virus.
manilatimes.net |
