National Wildlife Health Center

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Wildlife Health Bulletin #05-02

To: Natural Resource/Conservation Managers  
From: Leslie Dierauf, Director, USGS National Wildlife Health Center
Title: Update on Avian Influenza in Wildlife
Date: July 2005

This is a follow-up to Wildlife Health Bulletin 04-01 that the USGS National Wildlife Health Center distributed in February 2004 on the H5N1 Highly Pathogenic Avian Influenza (HPAI) virus in Southeast Asia. Bulletin 04-01 is available at:

The current series of outbreaks of HPAI H5N1 in Southeast Asia can be traced to outbreaks in 1997 in Hong Kong, where it was first documented that humans could become infected with the influenza virus by direct contact with poultry. Since 1997, HPAI H5N1 has spread to ten countries in Southeast Asia (; Thailand and Vietnam have been the most severely affected. More than 200 million domestic chickens and ducks have died or been destroyed in attempts to control the spread of HPAI H5N1. As of July 2005, 109 human cases have been reported and 55 people have died. Currently, there is no evidence of sustained human-to-human transmission of HPAI H5N1.

Concern about wild birds infected with HPAI H5N1 increased when migratory waterfowl began dying at Qinghai Lake Nature Reserve in western China in May 2005. Over 6,000 birds have died so far. Bar-headed geese, great black-headed gulls and brown-headed gulls are among the species affected. Nature and Science recently published studies that showed that these birds were infected with HPAI H5N1 and that the Qinghai H5N1 strain appears to be a new recombinant virus, combining genetic material from at least two other HPAI H5N1 strains. Bar-headed geese will be leaving the Qinghai Lake Nature Reserve to fly over the Himalayas during migration to their wintering grounds in India, Bangladesh, and other parts of Asia, and there is concern that they may be able to spread the HPAI H5N1 during the upcoming migration.

Traditionally, waterfowl and shorebirds have been reservoirs for many strains of avian influenza, but they rarely fall ill from these viruses. However, the current HPAI H5N1 strain has caused mortality in over 40 species of wild birds, including geese, ducks, storks, egrets, herons, and falcons, as well as some mammalian species. It is unknown whether waterfowl and shorebird species infected with the current strains of H5N1 will become reservoirs, or whether they will become carriers of the virus during migration. Presently, there is no clear evidence that migratory birds have spread the HPAI H5N1 strain to new locations.

From some reports about the outbreaks of H5N1 in Asia, it is difficult to determine whether the infected waterfowl have been from captive or backyard flocks or from the wild. The full host range of Asian bird species that are susceptible to infection by H5N1 is unknown. Furthermore, the local movements, migration patterns, source and outcome of infection, and the potential of each bird to carry and shed the H5N1 virus are not currently known.

Currently, the implications of HPAI H5N1 for North American wildlife remain unclear. If migratory birds carry and shed the virus along flyways, the potential exists for the virus to spread into additional migratory species and for the subsequent spread of the HPAI H5N1 virus into other parts of the world including Europe, Australia, and North America. As noted, it is unclear whether infected birds are capable of migration, and carrying and shedding the virus.

When evaluating the risks of migratory birds spreading the HPAI H5N1 virus, many factors must be taken into account. There is considerable variation between species susceptibility and response to any given disease. This, combined with the different behaviors, ecology, geography, migratory pathways, and interactions among and between species, presents a very complex picture of avian influenza and associated risks for spread via migratory birds. For more information about wild birds and H5N1, see ProMED-mail, June 25, 2005 (, archive 20050625.1786).

Bird migration is only one of the possible routes of introducing HPAI H5N1 to the North American continent. Travel by infected people, along with contaminated luggage or clothing, and transportation of infected poultry, including the smuggling of illegal pet birds, and other poultry equipment and products, are more direct means to transport the virus.

The NWHC has the capability to detect HPAI H5N1 and is screening select submissions for avian influenza. The availability of molecular technology has enabled NWHC to test for the influenza viruses that carry the H5, H7 (another possible poultry pathogen) and N1 subtypes. The NWHC, with assistance from others, will also conduct targeted surveillance of aquatic birds for avian influenza and will continue to assist in disease investigations of wildlife mortality events.

Please contact the USGS National Wildlife Health Center at 608-270-2400 to report observations of sick and dying waterfowl. For guidelines on how to safely handle sick or dead wildlife, visit

For additional information about HPAI H5N1, visit

Centers for Disease Control and Prevention, Spread of avian influenza viruses among birds: Centers for Disease Control and Prevention (CDC) online,, accessed 06/20/05.

Chen, H., Smith, G.J.D., Zhang, S.Y., Oin, K., Wang, J., Li. K.S., Webster, R.G., Peiris, J.S.M., and Guan, Y. 2005, H5N1 virus outbreak in migratory waterfowl: Nature online,, accessed 07/06/05

Chen, H., Deng, G., Li, Z., Tian, G., Li, Y., Jiao, P., Zhang, L., Liu, Z., Webster, R.G., and Yu, K., 2004, The evolution of H5N1 influenza viruses in ducks in southern China: PUBMED online,, accessed 06/20/05.

Liu, J., Xiao, H., Lei, F., Zhu, Q., Qin, K., Zhang, Xiaowei., Zhang, Xinglin, Zhao, D., Wang, G., Feng, Y., Ma, J., Liu, W., Wang, J., and Gao, F., 2005, Highly pathogenic H5N1 influenza virus infection in migratory birds: Science online,, accessed 07/11/05.

World Health Organization, 2005, Cumulative number of confirmed human cases of avian influenza A/(H5N1) reported to WHO: World Health Organization (WHO) online,, accessed 07/07/05.


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