Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2002
Publication Date: 9/1/2003
Citation: Suarez, D.L., Spackman, E., Senne, D. Update On Molecular Epidemiology Of H1, H5 and H7 Influenza Infections In Poultry In North America. Avian Diseases,2003, 47:888-897.
Interpretive Summary: Avian influenza virus is normally a virus of wild birds like ducks and gulls. However, these wild bird viruses can infect other species including chickens and turkeys. The avian influenza virus in these new species can cause serious disease outbreaks, especially if the virus is allowed to infect birds over a long period of time. Influenza viruses can be sequenced, where their precise genetic code is determined. The sequence for any new outbreak of influenza is usually a unique identifier of that virus that can be distinguished from all other influenza viruses. This allows us to compare a newly discovered virus with other sequenced viruses to see if they are related. This technique was used for recent outbreaks of H1, H5, and H7 subtypes of influenza in the U.S. It was determined that a recent outbreak of H7 influenza in Virginia and North Carolina was related to viruses isolated from the Northeast U.S. live bird markets. Several unrelated H5 outbreaks were observed in different parts of the U.S., and an unusual H1 virus appeared for the first time in turkeys from Virginia.
Technical Abstract: Avian influenza is endemic in wild birds in North America, and the virus routinely transmitted from this reservoir to poultry. Influenza, once introduced into poultry, can become endemic in the poultry population, it may be successfully eradicated by human intervention, or the virus may fail to successfully spread on its own. In the last five years, influenza has been isolated from poultry in the U.S. on numerous occasions, and most of the isolations have been associated with the live bird markets in the Northeast United States. This has included primarily H7N2 influenza viruses, but also H7N3, H5N2 and other influenza subtypes. Most of the H7N2 viruses were part of a single lineage that was first observed in 1994, but new introductions of H7N2 and H7N3 were also observed. The predominant H7N2 LBM lineage of virus spread to large commercial poultry operations on at least three occasions since 1997, with the largest outbreak occurring in Virginia in 2002. The H5N2 viruses in the LBMs included viruses from domestic ducks, gamebirds, and environmental samples. Some H5N2 viruses isolated in different years and in different locations had a high degree of sequence relatedness, although the reservoir source, if it is endemic, has not been identified. Finally, a H1N2 virus, associated with a drop in egg production, was isolated from turkeys in Missouri in 1999. This virus was a complex reassortant with swine, human, and avian influenza genes that was similar to recent swine isolates from the Midwest. Additional serologic evidence suggests that flocks in other states were infected with a H1N2 virus.