If a virulent strain of avian influenza ever struck the U.S. poultry industry, this country probably would fare better than many other nations due to careful biosecurity procedures in force.
But if the virus develops an ability to pass from one human to another, the United States would have far less protection as the world possibly faces one of the worst flu pandemics in history.
Among the U.S. health officials watching the progress of this extraordinarily active virus (known as H5N1) as it infects chickens in Asia and waterfowl in Russia, is Alfonso Torres, director of the Animal Health Diagnostic Center and associate dean for veterinary public policy at Cornell University's College of Veterinary Medicine.
"The fear is that if the virus changes or recombines with a regular human flu, the virus may acquire the ability to be effectively transmitted from human to human, then it could become the big pandemic that everyone is very concerned about," he says. As a consultant, Torres has held high-level policy discussions on avian flu with the U.S. Department of Agriculture (USDA) and NATO, among others.
For now, the United States, like the rest of the Western world, can only watch and prepare. Since January 2004, the known human cases of avian flu have all struck in Southeast Asia -- out of 120 patients requiring treatment, about half have died. All of these infections were contracted from chickens, with the exception of a few cases in Vietnam where the source is unclear.
A natural reservoir for the avian flu virus is migratory waterfowl, and infected birds have been found in Mongolia, Kazakhstan and Russia, raising concern in the U.S. as the disease moves west. Although waterfowl do not appear to be playing a big role in poultry and human transmissions right now, they are being closely monitored.
"When experts look at the maps of the areas affected by avian influenza in Asia and they look at the flying pathways of migratory waterfowl, there is not an overlap," Torres observes. Although waterfowl are the natural reservoir for all types of avian flu -- meaning they are long-term hosts of these viruses and pass them among each other, but often may not get sick or they develop mild infections -- Torres says, "Waterfowl, at this point in time, are not the culprit for what is happening in Asia."
Rather, the disease has spread in Asia in backyard and low-tech poultry and duck production areas where people transport infected chickens atop cars or on motorbikes to markets. There, sick birds can infect other birds that then return home unsold. Also, people who handle uncooked meat and infected birds can spread the flu virus from bird to bird.
But in Asian poultry farms that use modern biosecurity practices, like those in the United States that prevent infectious diseases from spreading through flocks, the disease has not spread. U.S. biosecurity regulations serve to minimize contact between poultry and outside materials that could bring disease. For example, measures can require poultry farm workers to take showers upon entering a production facility and when they move between birdhouses on the farm, and restricts them from owning pet birds at home and from hunting ducks and other waterfowl.
As long as the disease stays primarily a bird flu, officials have some control, says Torres, a former U.S. chief veterinary officer and director of the Plum Island Animal Disease Center, a high-security animal laboratory previously operated by the USDA but now part of the Department of Homeland Security.
While H5N1 strain most concerns researchers because of its virulence and ability to be transferred from birds to people, all strains that include the H5 and H7 proteins are now monitored because they are most commonly affect poultry and they could potentially mutate into more virulent, contagious forms.