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Pigeons unlikely bird flu threat

Although pigeons are not immune from the virus, tests indicate the birds pick it up only when they are exposed to very high doses, do not always become infected under those conditions, and are carriers only briefly.

Government scientists looking for the first signs of the H5N1 bird flu strain in the United States are focusing on wild migratory birds, not resident birds such as pigeons, starlings, and sparrows that stay close to home.

There have been no pigeon die-offs in parts of the world experiencing H5N1 outbreaks, according to USGS wildlife disease specialist Grace McLaughlin.

In one experiment, researchers squirted into pigeons' mouths liquid drops that contained the highly pathogenic H5N1 virus from a Hong Kong sample. The birds got about 100 to 1,000 times the concentration that wild birds would encounter in nature. They couldn't infect the pigeons.

In 2004, the lab did two more experiments. Using a pigeon and a crow that had both died in Thailand, researchers gave 12 pigeons similarly high doses of the bird flu virus. Seven became infected and one died. Five others did not become infected. That tells researchers that pigeons can be susceptible. But they're not uniformly susceptible.

Infected pigeons carried the virus about 10 days. But they were infectious for only about two days and then at levels below what it would normally take to infect a chicken. The experimental data shows that pigeons are unlikely to be spread the virus around.

FAO says human activities, not wild birds, spread H5N1

The UN’s Food and Agriculture organization says it is unreasonable to blame wild birds as the source of H5N1, in the absence of rigorous research into their role in the ecology and dynamics of the virus.

“It is indeed likely that (wild birds) can introduce the disease to unaffected areas from countries in which the disease has already been identified," the FAO’s statement asserts, "But the disease is spread through the human activities of poultry production, improper hygiene, and uncontrolled commercialization."

More research is needed to understand wild bird migration and the vulnerability of different species.

"Surveillance for avian influenza viruses and the presence of the HPAI H5N1 virus in wildlife can be given priority only once adequate surveillance of the poultry sector is in place, since poultry are more likely to transmit infection to humans and other susceptible animals,” the statement adds. “To devote resources to monitoring wild birds rather than take stock of production practices and improving such practices would not be justified."