The $30 billion United States poultry industry is the largest in the world. Poultry farms and live bird markets are tightly regulated by the U.S. Department of Agriculture to keep them free of disease. Now, with the outbreak in several Asian countries of the highly contagious H5N1 avian influenza, which has led to the slaughter of millions of birds and the death of 60 people, U.S. poultry regulations have taken on new urgency.

Intensifying the focus on animal disease and surveillance is the National Animal Health Laboratory Network, comprised of a dozen state-run facilities. One is on the Cornell University campus in Ithaca, New York, where avian influenza is now a top priority.

Every day a Styrofoam cooler with dry ice is delivered to Cornell University's Animal Diagnostic Laboratory. In it are test tubes with respiratory and fecal samples from live bird markets in the New York region.

Benjamin Lucio-Martinez, an avian disease expert in the school's Veterinary Medical Center who works with poultry farmers in both backyard and commercial operations , says his mandate is to isolate factors that cause disease in chickens. "If there is a drop in egg production, which doesn't even kill the chickens, we try to determine why that happened," he says and adds, "If there are chickens dying, then it is even more important, because the losses will be higher. And since the hype on H5N1, it has become a priority to determine the cause of death of even a few chickens."

Avian influenza is an airborne respiratory virus that spreads rapidly from bird to bird through contact with manure, eye or nasal excretions. Forty percent of live bird markets in New Jersey and 25 percent in New York - the largest chicken supplies in the nation - tested positive at least once for the disease last year.

Fortunately, those strains were not the H5N1 variety, and none have been virulent. That wasn't the case in 1983 in Pennsylvania where an outbreak of another lethal strain of bird flu forced authorities to slaughter 17 million chickens.

The laboratory at Cornell wants to avoid that.

Each sample is closely studied. Samples are passed through a centrifuge to get rid of debris and then are treated with antibiotics to kill any bacteria. Then, as Dr. Lucio-Martinez explains, technicians dressed in protective gear and gloves carefully inject the sample into healthy chicken embryos.

"The chicken eggs come from our own flocks, flocks that are specific pathogen free flocks," he says. "Those flocks have not been vaccinated for any disease and they have not been exposed to common diseases of chickens. So they are free of antibodies and the eggs from these chickens allow a better growth of the virus."

The tiny hole in the shell is sealed and the chicken eggs are put back into an incubator and checked daily for four days. The ones that die are processed and tested for the infectious H5 or H7 virus. Dr. Lucio-Martinez says once a contagious avian virus strain is identified, New York State Agriculture officials follow strict protocols. "They go into that market. They close it down. They kill all the chickens and wash and disinfect it. They are not allowed to bring any more chickens until they retest and prove that they are negative."

Dr. Lucio-Martinez says it was more likely a few years ago to find an H5 or H7 virus. "Now they are more careful about whom the poultry dealers buy from," he says. "They buy from people they know who do not have a problem. So the number of isolations that we have been doing lately has markedly gone down. Most of the samples that we work with are negative and my personal feeling is that we will know about it even before it gets here because the chickens will be dying in the field."

Benjamin Lucio-Martinez says the H5N1 virus has the potential to devastate the U.S. poultry industry and, if it mutates to a form that can jump from human to human, could result in a deadly pandemic. But Dr. Lucio-Martinez says constant vigilance can help keep bird markets safe and identify problems before they get out of control.