Bird flu findings fly in face of assumptions
Scientists at the Institute of the Environment Center for Tropical Research help prove U.S. songbirds can carry the avian flu.
Originally published in UCLA Today
By Alison Hewitt
It's not easy getting 13,000 birds to fly in for a bird flu check-up.
But that's exactly what UCLA researchers were able to do, with the assistance of catch-and-release birding stations and colleagues across the country. Between 2005 and 2008, scientists from UCLA's Center for Tropical Research analyzed swab samples from birds of all feathers to explore a hunch that — contrary to a 30-year assumption that American songbirds are flu-free — songbirds actually carry the infection.
The UCLA researchers were right.
That's not to say songbirds are deadly. They carry a mild version of bird flu – the harmful H5N1 strain of bird flu has never been found in the United States, said Tom Smith, an ornithologist, center director and Professor of Ecology and Evolutionary Biology, who headed the joint EEB and Institute of the Environment-based project. The virus strain songbirds carry doesn't actually make birds or people sick. Only a small percentage of certain species of songbirds — American robins, Swainson's thrush, fox sparrows and a few types of finches, among others — turn out to be flu carriers, Smith said. Other songbird species — mockingbirds and scrub jays, for instance — received a clean bill of health.
The danger, Smith pointed out, is that these mild, "low-pathogenic" strains of avian influenza could recombine with flu strains from other animals to form new, potentially life-threatening strains.
Smith had suspected songbirds as flu carriers for years, even though the scientific community has long held that birds like ducks and chickens are the main vectors of bird flu, passing the virus on to humans on farms, for example.
"Songbirds had been overlooked," said Trevon Fuller, a postdoctoral researcher with Smith's team and lead author of the paper announcing the discovery.
Studies over the years consistently found that waterfowl and shorebirds carried the virus, Fuller said. The flu was hardly ever found in songbirds, perhaps because early research focused on a limited number of species and locations, he said.
But, said Smith, "I had a hunch we were going to find it." Where others saw flukes in the rare instances of bird flu in songbirds, he saw clues – and a much broader threat due to the songbirds' migratory natures. "If there were an outbreak, it wouldn't be localized — it would fly south for the winter and spread along the way," he said. Songbirds are also more likely than wild waterfowl to share habitats with pigs and poultry, animals in which the disease can recombine and spread.
Smith began to test his hunch in 2005, when the Department of Biology and Evolutionary Ecology received a grant from the Ecology of Infectious Diseases Program, a joint initiative of the NIH and NSF. At the time, the bird flu scare was at its height, with chicken-to-human transmissions causing deaths in China and Africa.
There was mounting concern that wild birds could spread the disease across borders. "There's no H5N1 in the U.S.," Fuller explained, "but there are birds that migrate, amazingly, from Asia clear to California." The government wanted to determine if birds presented a danger of flu transmission to American soil.
"What's really cool was Tom's idea to look for it in songbirds after people had ignored them for so long," Fuller added.
To obtain samples from birds nationwide, Smith collaborated with the Institute for Bird Populations, which has about 400 bird-catching stations all over the country. Several members of the UCLA team joined the stations to collect samples. They also made training videos and thousands of sample-collection kits.
Birds were caught mid-flight in hundreds of volleyball net-like "mist nets." After gently freeing the birds from the nets, researchers and volunteers swabbed the birds, then set them free. All told, the UCLA team analyzed 13,000 swabs, including 5,000 swab samples gathered by the institute, and thousands more from shared databases created by bird-flu researchers around the country.
The team was grateful when the birds flew south for winter, Fuller joked — it gave them time to analyze the samples they had collected the rest of the year.
The analysis itself proved tricky and led to a separate scientific breakthrough: It turned out to be problematic to identify the bird flu virus in the swabs. The swabs were stored in alcohol to preserve them, but the alcohol also degraded the samples.
Emily Curd, one of Smith's graduate students, developed a way to identify the virus from small fractions of its RNA. The unique technique can be applied to a wide range of scientific testing, said Fuller.
After Smith's team began finding infected songbirds, they had one more hurdle to cross: they needed proof that these birds weren't rare outliers that picked up the virus from chickens on farms.
Postdoctoral researcher Kristin Ruegg had that covered. She did her dissertation on Swainson's thrush, one of the songbirds identified as a bird flu carrier in the UCLA study. Swainson's thrush live far from farms. And people. And hotels. Ruegg spent three months living in a tent to research the birds. That proved they were carrying the flu independent of exposure to farms.
But other songbirds do visit farms, mingling with animals such as chickens, turkeys and pigs. Bird flu strains could flow between species and learn potentially dangerous new tricks. In the recent influenza pandemic H1N1, originally called swine flu, the virus was a bird flu that developed into a human flu in part by mutating with strains from pigs. Likewise, a benign bird flu like the type carried by songbirds can mutate and become fatal to poultry.
Using data modeling and GPS data, Fuller was able to create a hotspot map of the U.S. where bird flu concentrations are highest. He overlaid the hotspots onto a map where pig farms are plentiful and found that the Mississippi Flyway over Illinois, Iowa and Minnesota is at the greatest risk for an outbreak.
Ironically, the UCLA team discovered that farms appear to increase the risk of flu in wild birds. Large swaths of cropland force birds to crowd together in smaller natural habitats, and the crowding leads to easier flu transmission.
Making use of the wide-ranging information gathered in this research, UCLA researchers plan to keep a close tab on emerging strains of bird flu. Spotting the newest strains could guide the development of better, more targeted vaccinations.
Smith's team, which is now conducting a similar songbird study in Africa, recently traveled to an international conference in Germany to present their findings. Were other scientists smacking their foreheads for having overlooked songbirds for so long?
Smith was too polite to say so, but nodded thoughtfully. "I think," he said diplomatically, "that people are going to be much more interested in songbirds now."
Published: Monday, August 02, 2010