Relationships of influenza viruses and their hosts are overviewed as a historical process. First, infection by harmless avian influenza viruses is presented including a great diversity of hosts (wild aquatic birds) and viruses (Figure 1). Ancient evolutionary processes, such as delineations according to primary hosts and/or geography as well as creation of novel gene combinations by reassortments leading to present diversity are described. Then infections in secondary host species (chicken, man, horse and swine) emerged during civilization are outlined that were initiated with colonisation by primitive viruses from the natural hosts, a process that is still continuing (Figure 2). Disease forms which emerged in secondary hosts due to unnatural keeping of animals and change of virus properties are examined. The influence of these factors on the genesis of epidemics is also treated. Namely, the transition from sporadic forms, that manifests in outbreaks caused by highly pathogenic strains due to local mutation of their low pathogenic version, to typical acute epidemic (Figure 3). Circumstances, including high density poultry populations, mixed keeping of land-based poultry and water-fowls as well as multiple reassortment of viruses in the region are discussed as major factors in eliciting the unprecedented territorial spread of the current H5N1 Asian epizootic and the emergence of duck pathogenic strains that contaminated the natural reservoir.
|Translated title of the contribution||History of influenza virus infections with reference to H5N1 avian influenza outbreaks in East Asia|
|Number of pages||15|
|Journal||Magyar Allatorvosok Lapja|
|Publication status||Published - Dec 12 2006|
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