Beware the Starlings: Common birds can carry avian influenza

October 17, 2007 at 11:40 am

Starlings, introduced into North America from Europe in the 19th century, have become a widespread nuisance. And they just got more annoying: It turns out they’re good at carrying bird flu.

THREAT FROM THE AIR. Some common songbirds, like this European starling, could act as carriers of avian flu. iStockphoto

During the past two winters, common songbirds in Hong Kong “have been dropping dead out of the sky,” says Robert Webster, an infectious-diseases specialist at St. Jude Children’s Research Hospital in Memphis, Tenn. Some of those birds died from avian influenza. Webster and his colleagues wanted to know what role the birds might play in spreading the virus.

In a laboratory study, the scientists found that captured starlings infected with four strains of avian influenza breathed and defecated large amounts of virus. One uninfected starling picked up the bug from its cage mates—the first reported case of starling-to-starling transmission.

If highly pathogenic avian influenza ever arrives in North America—and there’s no evidence that it has—the experiment shows that the near-ubiquitous birds could serve as a reservoir for the disease, Webster and his colleagues report in the November Emerging Infectious Diseases.

“It’s the little songbirds like starlings that form the bridge, if you will, between waterfowl and poultry and people,” says Walter Boyce, executive director of the Wildlife Health Center at the University of California, Davis. At watering holes, for instance, songbirds often mingle with waterfowl, which later might mingle with poultry.

In other experiments, Webster’s team found that house sparrows and common pigeons did not spread the virus to others of their species. Sparrows dispersed large amounts of virus, but died 4 to 6 days after infection, making them poor long-term carriers. Infected pigeons showed no signs of illness and breathed and defecated only small amounts of virus, indicating that they, too, would provide a poor bird-flu reservoir.

Boyce says that the study “adds another piece of the puzzle. [But] there is not strong evidence these [common songbirds] are going to be an important source of virus for the other animals they’re in contact with.”

Since 1996, outbreaks of the H5N1 avian-influenza virus in Asia, Europe, and Africa have led to the culling of millions of poultry. Experts think that ducks and other waterfowl serve as the natural reservoir of H5N1, which is genetically distinct from the influenza viruses that circulate in the United States each winter.

Health authorities recorded the first human case of avian influenza in 1997, and 202 people have since died from the virus.

The high fatality rate of H5N1—61 percent of the confirmed human cases have resulted in death—worries public health officials. They’re concerned that the virus might mutate into a form that can spread from person to person, sparking a pandemic.