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Category: Clinical Microbiology
Understanding the Ecology and Epidemiology of Avian Influenza Viruses: Implications for Zoonotic Potential, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818050/9781555812010_Chap06-1.gif /docserver/preview/fulltext/10.1128/9781555818050/9781555812010_Chap06-2.gifAbstract:
In general, influenza viruses replicate in epithelial cells of the upper respiratory tract or gastrointestinal tract, and the outcomes of such infections include no clinical signs, upper respiratory disease, pneumonia, and occasionally death. In birds, most infections are subclinical. However, in poultry, influenza infections have caused clinical respiratory disease or drops in egg production, and a few specific avian influenza virus strains have caused severe disseminated infections with systemic disease and high death losses. Interspecies transmission between different hosts within separate classes is even less frequent, as has occurred rarely with chicken-to-human or free-flying duck-to-pig transmission. One exception to the above rule has been the ease and frequency of transfer of swine H1N1 viruses to turkey breeder hens, but these are sporadic and isolated occurrences. The ability of influenza viruses to spread and produce infectious progeny and lesions is related to the cleavage of the hemagglutinin in various cell types. In mammals, influenza viruses primarily replicate in the respiratory tract and cause associated clinical signs and lesions. Virus replication occurs predominantly in the epithelium of the nasal cavity and results in clinical rhinitis, the most frequent clinical presentation in human patients, horses, and pigs. In Minnesota, traditional and molecular epidemiology has demonstrated the direct transfer of mildly pathogenic avian influenza viruses from free-flying birds (primarily mallard ducks) to range turkeys reared outdoors during annual wild-bird migrations.
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Phylogenetic tree of nucleoprotein genes, showing the major influenza virus lineages in birds and mammals. (Courtesy of David L. Suarez, U.S. Department of Agriculture [USDA].)
Phylogenetic tree of nucleoprotein genes, showing the major influenza virus lineages in birds and mammals. (Courtesy of David L. Suarez, U.S. Department of Agriculture [USDA].)
Ecology of influenza viruses in various avian and mammalian hosts. LBM, live-bird markets.
Ecology of influenza viruses in various avian and mammalian hosts. LBM, live-bird markets.
Poultry species from multiple sources are mixed in the live-bird markets, where poultry pathogens such as avian influenza virus can be exchanged and maintained. (Photo courtesy of Martin Smeltzer, USDA.)
Poultry species from multiple sources are mixed in the live-bird markets, where poultry pathogens such as avian influenza virus can be exchanged and maintained. (Photo courtesy of Martin Smeltzer, USDA.)
Ecology of avian influenza viruses in the live-bird markets (LBM).
Ecology of avian influenza viruses in the live-bird markets (LBM).
Gathering of poultry during exhibition or recreational events such as illegal cock-fights in the United States provides the opportunity to exchange pathogens, including avian influenza virus. (Photo from an anonymous source.)
Gathering of poultry during exhibition or recreational events such as illegal cock-fights in the United States provides the opportunity to exchange pathogens, including avian influenza virus. (Photo from an anonymous source.)
Commercial turkeys raised outdoors for seasonal markets on occasion have had direct contact with migratory waterfowl and have been infected with mildly pathogenic avian influenza viruses. (Photo courtesy of Alex Bermudez, University of Missouri.)
Commercial turkeys raised outdoors for seasonal markets on occasion have had direct contact with migratory waterfowl and have been infected with mildly pathogenic avian influenza viruses. (Photo courtesy of Alex Bermudez, University of Missouri.)
A commercial broiler house sufficient to raise 20,000 chickens.
A commercial broiler house sufficient to raise 20,000 chickens.
Wholesale poultry market at Cheung Sha Wan (left) and one of 1,000 retail markets in Hong Kong that provide consumers with fresh poultry meat (right).
Wholesale poultry market at Cheung Sha Wan (left) and one of 1,000 retail markets in Hong Kong that provide consumers with fresh poultry meat (right).
Hemagglutinin subtype distribution among different birds (class Aves) and mammals (class Mammalia) a
Hemagglutinin subtype distribution among different birds (class Aves) and mammals (class Mammalia) a