2006-03-09-Vet's Work in Cambodia May Hold Clues to Spread of Avian FluUnderstanding Avian Influenza
2006-03-09-Vet's Work in Cambodia May Hold Clues to Spread of Avian Flu
From the front seat of a Land Cruiser, Martin Gilbert peered through his telescope at the rare, black-headed bustard mostly obscured by a tussock of grass. He watched as his colleagues in a white pickup truck inched toward the bird, trying to gingerly direct it toward a net stretched about 75 yards across the dusty flood plain.
The stakeout had lasted more than half an hour, and Gilbert's closely cropped red hair was growing moist in the late afternoon heat, sweat beading on his brow.
"C'mon, mate," he urged the bird in hushed tones. "You're almost there."
Suddenly, it scampered into the open.
"Oooh! Oooh!" Gilbert exclaimed. "He's in the net! He's in!"
A globetrotting veterinarian now stalking bird flu across East Asia, Gilbert was eager to get hold of the bustard, called a Bengal Florican, so he could strap on a satellite transmitter to track its migration and take a fecal swab to test for the virus.
Although avian flu has been prevalent in Asia for at least three years and hopscotched to Europe and Africa, there is no consensus among health experts about the role migratory fowl play in spreading the disease and remarkably little knowledge about which species could do so.
These questions have acquired new urgency in recent weeks after wild birds introduced the virulent H5N1 strain into Western Europe. Gilbert's hunt in the wilderness of northwestern Cambodia could provide crucial clues about the role wild birds play in spreading the disease, even helping answer whether bird flu will ultimately arrive on American shores and how it might get there.
It has already struck birds in as many as 40 countries and infected at least 175 people, killing slightly more than half, according to the World Health Organization and other U.N. agencies.
Influenza specialists blamed the initial outbreaks in East Asia on the movement of infected poultry, saying farming and marketing practices have kept the virus circulating once it has been introduced into new countries in Asia and elsewhere.
Then, last year, an outbreak was reported for the first time among wild birds in Mongolia. Gilbert, the son of two Scottish country veterinarians, drove more than two days over a barren landscape to reach the remote site so he could catalogue the birds and take samples. It was one of the earliest indications that migratory fowl were carrying bird flu.
The World Health Organization reported late last month that mutations in the virus now allow it to infect some wild birds without killing them, potentially accelerating the spread of the disease over long distances. The genetic change had been noted after bird flu started racing westward last year from China across Central Asia to Turkey, a swath of the Earth little studied by ornithologists.
"The region from Asia to Europe is a kind of black hole in terms of what we know," said Malik Peiris, an influenza expert at the University of Hong Kong.
Although large numbers of infected birds have been found dead, he said those species may not be the long-haul carriers of the disease. "The real culprits who are doing the movement you probably don't see," Peiris said. "They're probably healthy. Obviously, if they're sick, they would not be able to migrate."
The utter dearth of information about the role of migratory fowl is hampering containment efforts.
"What would help with the wild bird situation is to know which species are the ones infected and moving the disease so we can pay attention to protecting poultry from them," said William B. Karesh, director of the field veterinary program at the New York-based Wildlife Conservation Society. "We can't be worried every day about thousands of species of wild birds. We need to figure that out."
Gilbert, 31, a former high school rugby player, worked with eagles in Panama and Papua New Guinea, falcons in Greenland, owls in Madagascar and vultures in India and Pakistan before signing on as the Wildlife Conservation Society field vet in East Asia two years ago. Bird flu was just starting to ravage chickens and ducks across the region.
Last week, Gilbert turned his binoculars on the flood plain of Cambodia's Tonle Sap Lake, the largest body of fresh water in Southeast Asia. During the rainy season, the lake inundates a vast expanse of northwestern Cambodia. But the water recedes in the dry season, revealing several thousand square miles of grassy plain, scrubland and even forest that provide a unique wintering ground for migratory birds.
When Gilbert's team finally trapped the florican, a British graduate student clasped the handsome bird and Gilbert tied a 40-gram transmitter to its back, looping the straps around its neck and behind its white wings, grimacing as he struggled to get a tight fit. The gadget was similar to those that U.N. officials plan to attach to scores of migratory fowl in the coming months in an effort to track the global spread of bird flu.
Before releasing the creature, Gilbert snapped on a pair of rubber gloves and took four fecal swabs. Two would be sent to the Cambodian government. Two would be tested at U.S. labs and added to the Wildlife Conservation Society archive with other samples he will collect elsewhere in the region.
Some wildlife conservation groups had long resisted the claim that migratory birds were spreading the virus, suggesting instead that the shipment of infected poultry and poultry products offered a better explanation. In this view, wild birds caught the virus locally from sick chickens and ducks.
But these groups revised their opinion after the virus last month killed swans and other wild birds in Europe, particularly in Germany and Italy, where there were no associated reports of sick poultry.
"Recent outbreaks in Europe are showing us that wild birds can carry the virus," said Leon Bennun, director of science and policy for Birdlife International, in Cambridge, England. "What we don't know is how long."
Bennun and some other wildlife experts still balk at the conclusion that migratory fowl are moving the virus over great distances. If wild birds had carried it west from China, these specialists say, there should be outbreaks all along their flyways. Reported cases, however, are few and sporadic.
But other researchers, such as Peiris, say there is already decisive evidence of long-distance transmission. They note that virus samples from recent outbreaks in Nigeria, Europe and Turkey are practically identical to those from a massive outbreak last year in wild fowl at China's Qinghai Lake, which killed 6,000 birds from five migratory species. Peiris said such uniformity would not result if the virus was conveyed by commercial poultry shipments.
As for the lack of confirmed outbreaks all along the migratory routes, these researchers suggest that cases are probably widespread but that local animal health authorities in remote districts may fail to notice or report them.
"We don't really know what the virus is doing in Asia at all," Gilbert acknowledged after night had blanketed the flood plain and his team had retired to a villager's home for dinner and rice wine.
The next day, they set out for a neighboring province, looking to catch birds with a longer range than the florican. They turned off the road, navigating with a global positioning system about 10 miles down a dirt track and five more along a viciously rutted ox cart path until they penetrated an area of the flood plain where thorn bushes and elephant grass rose well above the roofs of the two vehicles.
An advance team had already used a machete to slash narrow passages through the brush and stretched nets along them to snag perching birds. The researchers plucked warbler after small warbler from the trap, four species that all breed in northern China or Siberia, where they could potentially infect birds bound for Alaska. Those in turn might infect still others that later fly south into the continental United States.
Gilbert toiled past sunset by the light of his headlamp, taking samples with tiny swabs meant for the ears of newborn babies.
The researchers were back at it again hours later under the pastels of daybreak. This time they caught a pair of the particularly rare Siberian Ruby Throat.
Then, not long before they pulled down the nets, they trapped one last migratory bird, a small creature with broad white lines above its eyes and a patch of blue on its throat, fittingly named Bluethroat. They checked their guidebook to make sure of its range. Sure enough, this species migrates directly to Alaska, just one step removed from the lower 48 states.
Gilbert squinted as he swabbed the bird, carefully adding the sample to his collection.