Bird flu's U.S. flyby?

NATIONAL REPORT — For the first time in history, scientists could be on the forefront of predicting an influenza pandemic.

Recent outbreaks among poultry in the United States with no transmission to humans.

"We have never had the technology or the funding to be in the driver's seat that we are today," says Dr. Carol Cardona, Dipl. ACPV, avian influenza expert with the National Center for Foreign Animal and Zoonotic Disease Defense. "We know that a pandemic will undoubtedly occur at some point in our near future. But we don't know what virus that will be. The H5N1 looks like a good candidate, however, it might never, ever become a pandemic virus."

Despite the plague of media attention, H5N1 largely remains an avian flu with little immediate threat to the food supply or companion birds in the United States.

Still, the country's producers are under the microscope for the next killer bug, and border control has become a public health issue. About 38,000 animals cross U.S. borders each day, and the illegal exotic animal trade is a $4-billion to $6-billion industry, according to Dr. Lonnie King, director of the Office of Strategy and Innovation for the Centers for Disease Control and Prevention (CDC).

Recent North American outbreaks of avian influenza with transmission to humans

Smugglers could introduce an array of disruptive viruses to the country. Cockfighting organizers are thought to have introduced exotic Newcastle disease into the United States in 2002, resulting in millions of depopulated birds and a multi-national boycott of U.S. poultry products. Newcastle disease remains a virulent threat, says Dr. Thomas Tully, MS, Dipl. ABVP, president of the Association of Avian Practitioners and professor of clinical sciences at Louisiana State University.

"We are keeping our eyes on H5N1 for sure, but it's more likely that Newcastle would rear up than H5N1 at this point," Tully says. "We don't know if all the birds are going to respond to the virus, but we are trying to determine that. With West Nile, for example, some birds are more susceptible than others. With H5N1, there are certain birds that incubate a highly pathogenic strain that affects them, so there is a lot still up in the air."

Influenza pandemics during the 20th Century

Historically, the incidence of influenza in exotic birds is very low, says Dr. Susan Clubb, Dipl. ABVP, owner of Rainforest Clinic for Birds. Influenza has been detected only once in the 30 years the United States has observed a one-month quarantine for exotics, she says.

"If you look back at import records (according to the National Veterinary Services Laboratory) there has only been one occasion since 1974 where a pathogenic bird flu has come into the United States in exotic birds. That was in Peking Robins that came in from China," she says. "Now people are afraid to feed the birds in their back yard, and there is a state of fear that we are living in. Exotic birds are not the risk. The risk is in poultry and waterfowl."

Still, practitioners who see new patients have a duty to inquire about the origin of an animal to deflect a range of diseases. Many breeders in this country use aluminum identification bands that identify the producer to ensure companion birds are made in America.

"Practicing veterinarians need to be aware and encourage people to purchase only those birds that have been legally imported. That's an important safeguard that we need to protect at this time," says Cardona, who is also associate professor and cooperative extension poultry veterinarian in the University of California-Davis School of Veterinary Medicine.

Assessing risks

Stringent surveillance and reporting protocols already in place to monitor for food-safety risks routinely test flocks for avian influenza, among other diseases. More than a thousand broiler, layer, turkey, game bird and ostrich operations are monitored by the Animal and Plant Health Inspection Service (APHIS) National Poultry Improvement Plan (NPIP). The program was developed with industry, state and federal cooperation to identify and eradicate infectious diseases; 48 state agencies and 130 authorized laboratories monitor close to 10,000 flocks comprised of about 85 million birds for avian influenza. Most are broilers.

"Right now, the risk of H5N1 coming into our birds is very low," says Dr. C. Stephen Roney, Dipl. ACPV, director of Veterinary Services for Goldkist, a producer with more than 2,300 family farmers in the Southeast that produce 14 million chickens a week. "There have been times when animals in live-bird markets or migratory water foul have had some low-path viruses that bleed over into commercial flocks, but we find them in our routine monitoring."

The need for NPIP became clear after an outbreak of exotic Newcastle disease in Southern California in 1971 threatened the industry. The outbreak in California was finally eradicated in 1974, but not before it infected 1,341 flocks resulting in the depopulation of 12 million birds at a cost of $56 million.

The disease reared again in 2002-2003, when an outbreak in a non-commercial flock in California eventually spread to 22 commercial flocks in the state, resulting in culling 3.9 million birds. Small outbreaks also occurred in Nevada, Arizona and Texas before the disease was wiped out. According to APHIS, the event had a significant economic impact on the U.S. poultry industry due to prohibitions on U.S. poultry imports by Canada, Mexico, China, Japan, Korea, the Philippines, Poland, Tahiti, Taiwan, the European Union, Argentina and Guam. The United States exports approximately $2.5 billion worth of poultry a year, according to the National Chicken Council.

That economic impact is a serious concern for producers at home, too, as the fowl plague could fuel uncertainty among consumers.

"With the current panic and scare that is going on in the media, I'm afraid that there might be some unfounded panic and fear, even if we had a virus that was really harmless," Roney says.

U.S. poultry industry revenues neared $30 billion in 2004.

So what's the hype?

It's not all Chicken Little. The first outbreak of H5N1 that occurred in Hong Kong in 1997 proved that a purely avian virus could infect people directly. Previously, pigs were thought to be the obligatory mixing vessel for re-assortment of viruses because they possess receptors for both avian and human influenza viruses on the cells of their respiratory tract. Now, people could serve as a mixing vessel, which signaled that a pandemic might be imminent, according to the World Health Organization.

Although the virus has 90-100 percent mortality rate in infected flocks and a 50-percent mortality rate in humans, little is known about the possibility of immune response.

"We know of the people and animals that were infected and became sick, almost half of those appear to have died, but we really don't know if there are individuals who are being exposed to the virus and setting up an immune response and not becoming seriously ill." says Yvette J. Johnson, DVM, MS, PhD, assistant professor of clinical epidemiology and poultry species veterinarian for the University of Illinois College of Veterinary medicine. "With West Nile virus, we found out a lot about the people who became severely ill and had high death rates, but later on after looking at antibodies circulating in the population, we found out that most people were exposed and either didn't know they were sick or were mildly sick and moved on. That type of work hasn't been done yet."

Migratory waterfowl appear to be the main vessels for spreading the disease. Though the lion's share of commercial U.S. poultry are raised indoors, many fear that backyard flocks, subsistence farmers and some local producers who mainly sell their livestock at live-bird markets could expose their poultry to diseases from wild, migrating waterfowl. Then, the tainted birds commingle with those from other operations. A busy live-bird market could be ground zero if a highly pathogenic strain infiltrates the United States.

"Especially on the east coast and other major urban areas, people purchase live chickens for home consumption," says Johnson, who is also part of the International Society of Veterinary Epidemiology and Economics. "Then you have birds that have not necessarily been reared in the types of conditions seen the usual commercial poultry operation, and then those birds are being transported and mixed with an assortment of animals during the sale process. So you've got a situation where potentially, the virus can then spread."

Ponds that attract wild waterfowl were present on the property of more than 38 percent of backyard flocks, according to Poultry '04, a study by the National Animal Health Monitoring System of the U.S. Department of Agriculture. More than half of the backyard flocks surveyed that raised domestic waterfowl had a pond on the property that attracted wild waterfowl. About 1.2 percent of the premises obtained birds from outside the United States.

Some fear migrating birds from Asia could cross the Bering Straight into North America. Canadian public health veterinarians are randomly testing wild geese and ducks for the virus in six of its 10 territories. In October, a low-pathogenic H5 avian flu was found in 33 wild ducks in Quebec and Manitoba.

"H5 is not uncommon here in the United States or Canada, but it's not the same H5 that is in Asia," Cardona says. "Vets who have clients with backyard poultry or small flocks of poultry, this is the year that they need to talk to them about building a coup and keeping those birds indoors. If they are allowed outside access, it should only be for a brief period, and they should keep their food and water covered."

Biosecurity begins at home

With so many questions still up in the air, basic biosecurity protocols should be in place for all producers and practitioners, especially during flu season.

"With the other zoonotic diseases that we encounter every day, it's important to practice those same safegards with poultry as well as all birds, as you do with any animal," Cardona says. "For practitioners, the most likely thing that they need to worry about catching themselves during this upcoming flu season is actual flu epidemic that takes place every year. That's nothing to laugh at because it's an epidemic that kills 36,000 Americans in a normal year, so it's important to encourage employees to stay home when they are sick, cover their coughs and wash hands frequently."

The CDC recommends that all healthcare workers get a flu shot; that includes veterinarians, Johnson says.

"We need to be reminded of our role in public health and that protecting ourselves and our employees by using good biosecurity and educating our clients for the potential of exposure to disease from animals, whether their pets or meat at the grocery store," Johnson says. "We shouldn't be afraid, but the same types of precautions that we take when people are sick, we need to take those precautions when our pets are sick."