Experts at AAAS Forum Assess the Spread of Avian Flu in Birds, People

While health authorities are paying close attention to the possible spread of avian flu to the United States, a leading bird researcher says it is incorrect to assume that migratory birds will be the primary culprits.

“You actually have to have the smoking gun,” says Peter Marra, a senior scientist with the Smithsonian Institution’s Migratory Bird Center. “You have to have an individual [bird] that’s migrating that is also carrying the virus to the point where it can actually shed the virus. And that’s difficult.”

Specialists are trying to sort out the role of migratory birds in spreading the virus compared to that of infected poultry or wild birds traded legally or on the black market. Experts discussed the role of birds in spreading the disease—and a range of human preparations for a possible human pandemic—on Thursday 20 April at the 31st annual AAAS Forum on Science and Technology Policy in Washington, D.C.

Marra said it is difficult enough to determine the precise migration patterns of wild birds, much less find birds in the active process of shedding flu virus. He also said that the widely published flyways maps for migratory birds offer only a “gross oversimplification” of the true flight patterns of specific birds. “They are useless for truly understanding the movement of a virus,” he Marra said.

For most species, Marra said, researchers still don’t know the flyways used by specific populations or the strength of their “migratory connectivity,” how reliably the same populations of birds return to the same locations each year for breeding and over-wintering.

Still, Marra, who spoke at the 31st annual AAAS Forum on Science and Technology Policy, said that migratory birds certainly do have the potential to spread the avian flu to North America and other regions as yet untouched by the disease.

The virulent H5N1 strain emerged in Asia and has spread to birds in Russia, the Middle East, Europe and Africa. More than 190 cases have been reported in humans, with 110 deaths. The cases have involved people who have had close contact with infected birds or their handlers.

Marra and several colleagues have studied the probable pathways for several dozen outbreaks of the H5N1 bird-flu strain since 1997. In about 20 outbreaks, scientists found evidence consistent with migratory birds moving H5N1 virus and 12 outbreaks where the poultry trade appeared suspect. Three were the result of trade in wild birds and 11 had unknown causes.

While the H5N1 virus has been spreading to bird populations in many locations, health authorities stress that it has yet to acquire the ability to spread readily by human-to-human contact, a prerequisite for a global flu pandemic in people.

“Obviously, it’s a pandemic if you’re a bird, but it’s certainly not a pandemic if you’re a person,” said Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention, said during a luncheon address at the AAAS Forum.

Gerberding said the potential for a pandemic poses serious challenges for public health authorities at all levels. By one estimate, 1.9 million ,900,000 Americans could die in a flu pandemic similar to the one that occurred in 1918 and nearly 1.5 million 1,485,000 could require critical care.

Linda Lambert, chief of the respiratory diseases branch at the National Institute of Allergy and Infectious Diseases, said ongoing studies of a vaccine against the H5N1 bird-flu strain have been promising, although the dose of vaccine required to provoke an immune response is significantly higher than with vaccines for other flu strains. Researchers both here and abroad have been looking at use of adjuvants such as aluminum hydroxide to increase the potency of each vaccine dose.

While it is unclear whether the H5N1 virus now circulating in birds will eventually trigger a global pandemic in humans, Lambert said that close surveillance and study of the virus will provide information that could help prevent some of the more than 36,000 deaths each year in the United States from the usual seasonal flu outbreaks.

Cecile Viboud, a research scientist at the Fogarty International Center[http://www.fic.nih.gov/] of the National Institutes of Health, described efforts to do mathematical modeling of the possible course of a flu pandemic, based on past experience with the devastating 1918 outbreak and milder pandemics in 1957 and 1968. She said Based on the available historical data suggest that , she said, health authorities should expect a preliminary outbreak about six months to a year before the full-blown pandemic. The transmissibility of the virus—how fast it spreads—is typically greater for a pandemic than a regular seasonal outbreak, Viboud said.

Viboud is principal author of an article in the 21 April issue of Science that modeled the possible spread of a flu pandemic throughout the United States. The study suggests the virus could become widespread in as little as two to four weeks if the outbreak started in California. The model relies on three decades of data on seasonal influenza epidemics, where commuters traveling to their places of work play a significant role in the interregional spread of the illness. While such models are useful guides for policy makers, Viboud said, “Llike weather forecasts, epidemiologic predictions come with uncertainty.”

Meghan Thompson, senior editor in the corporate communications department of Citigroup, discussed steps her company, with 300,000 employees in more than 100 countries, has been taking in anticipation of a flu pandemic. Citigroup estimates that 30 percent of its workforce could be out during the peak of a pandemic, but . The the company must be able to provide continuity of business. , Thompson said. “We need to be able to assure people that their finances are safe,” she said.

Citigroup has started to stockpile some materials, including face masks, and has been working to develop consistent plans on absenteeism across many locations and cultures, Thompson said. One message, she said, is that an employee can do more harm to the company by bringing in the illness and spreading it to colleagues than by staying home. Citigroup also has been drawing lessons from the 2003 outbreak of SARS (Severe Acute Respiratory Syndrome), a deadly illness that emerged in Asia and spread to more than two dozen countries worldwide. In some cases, she said, company officials spent too much time in conference calls reporting on what they were doing rather than actually managing the crisis.

Peter Sandman, a risk communications consultant in Princeton, N.J. and adjunct professor at Rutgers University, said that public officials and health authorities often have a “fear of fear” and imagine that any scary messages about bird flu will inevitably cause people to panic. But panic is extremely rare, Sandman said, adding People “don’t do unwise, self-defeating, harmful things.”

“To want people to take precautions but to not want to scare them doesn’t make sense,” Sandman said. He said fear has a positive value and motivates people to take precautions. When people are unsure or ambivalent about how worried they should be about an impeding crisis, Sandman says, they often become more alarmed when officials seem too reassuring. The goal is to help people cope with their fears, he said, “rather than telling them they are jerks for feeling that way.”

Earl Lane

26 April 2006