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New research predicts US entry of H5N1 avian influenza

December 05, 2006

Scientists at the Consortium for Conservation Medicine (CCM), the Royal Society for the Protection of Birds, and the Smithsonian Institution's National Zoo report that H5N1 avian influenza is most likely to be introduced to countries in the Western Hemisphere through infected poultry trade.

Following the initial outbreaks of H5N1 avian influenza in Hong Kong, scientists and government officials worldwide have debated exactly how the virus was being spread and what could be done to stop it.

Dr. Marm Kilpatrick, senior research scientist with the Consortium for Conservation Medicine, led the team in their efforts to predict the most likely method of introduction to the U.S. Dr. Kilpatrick and colleagues predict that bird flu will most likely be introduced to countries in the Western Hemisphere through infected poultry trade rather than from migrating birds from eastern Siberia, as previously thought. The subsequent movement of infected migrating birds from countries south of the U.S. would be a likely pathway for H5N1 avian influenza to reach the USA.

The research will be published online in the Proceedings of the National Academy of Sciences in December.

Avian influenza has reached more than 50 countries, and millions of chickens have been either infected and/or culled to prevent the spread of the virus to other poultry farms. Estimated financial losses are in the tens of billions of dollars from its spread. In addition, 258 people have been infected and 153 human deaths have occurred, with most cases in Vietnam, Indonesia, Thailand, and China.

This new research set out to identify the pathways for individual H5N1 introductions as the virus spread through Asia, Europe and Africa. The predictive modeling approach used by the researchers offers substantial promise for understanding past introductions, the pathway for new introductions, and ways to prevent future spread of the deadly virus.

The researchers analyzed the risk of introduction by three different pathways: poultry, wild bird trade, and the movement of migratory birds.

"In order to determine the pathway of introduction we gathered global data on the country-to-country trade in poultry and wild birds and mapped out the migratory routes of every species of duck, goose, or swan. We then compared our analyses basedon these data to the relationships between virus isolates from the different countries," said Dr. Kilpatrick.

Dr. Robert Fleischer, a Smithsonian Institution scientist noted, "The rate of genetic change of the virus is extremely fast, and both the evolutionary and geographic pathways of the virus can be traced from the phylogeny over just the past three or four years."

The findings showed that migratory bird movements were likely responsible for three introductions in Asia, 20 in Europe, and three in Africa. Dr David Gibbons, Head of Conservation Science with the UK's Royal Society for the Protection of Birds, said "Much of the spread of H5N1 around Europe followed an unusually cold period of weather in central and eastern Europe in January and February 2006, with wild birds moving west through Europe in search of more clement conditions, some carrying H5N1 with them. As part of the UK Government's AI surveillance strategy, RSPB staff will be looking for sick or dead ducks, geese and swans this winter."

Dr. Peter Marra, an avian ecologist with the Smithsonian's Migratory Bird Center at the National Zoo commented, "In almost all cases in which we have detected H5N1 in wild birds, it has been found in dead birds. It's critical that dead bird surveillance mechanisms be developed for the early detection of not only H5N1, but also the next pathogenic avian disease to come along."

In comparison, poultry trade was responsible for two bird flu introductions to countries in Africa and nine important introductions in Asia where the disease is still infecting humans and poultry. "The synergistic combination of poultry trade and migratory bird movements spread H5N1 much further than it would have gone by either of these pathways alone," said Dr. Kilpatrick.

Dr. Peter Daszak, Executive Director of CCM, "This study shows how trade between continents opens the door for pathogens to move effortlessly along those routes." Daszak added, "The study of Conservation Medicine strives to understand how human activities drive disease spread and proposes critical action steps on preventing future pandemics."

Donald Burke, Dean of the University of Pittsburgh Graduate School of Public Health, and an advisor to the group, emphasized the importance of a globally coordinated and forward thinking approach to pandemic threats. "This report shows that it is possible to move beyond the conventional 'surveillance and response' mode to one of 'prediction and prevention' he said.

Dr. Mary C. Pearl, President of Wildlife Trust and a co-founder of the CCM noted, "Fully three-quarters of new diseases have an animal origin. By researching the links between wildlife, livestock, and humans, we can better identify the movement of many new disease-causing agents - not just avian flu - before they move to people."

Dr. Leslie A. Dierauf, Director of the USGS National Wildlife Health Center, an institutional partner in CCM, expressed the need for additional field and laboratory research into the biology and epidemiology of avian influenza viruses in wild migratory birds -"Such research is integral to our preparedness for the anticipated arrival of HPAI in North America. It is critical to gather data to further inform predictive models necessary to track this emerging disease and stem its spread among wild birds and domestic poultry and its potential transmission to other wildlife, pets, and people.\\\

Smithsonian