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Category: Bacterial Pathogenesis; Clinical Microbiology
The Role of Punctuated Evolution in the Pathogenicity of Influenza Viruses, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555819453/9781555819446_Chap06-1.gif /docserver/preview/fulltext/10.1128/9781555819453/9781555819446_Chap06-2.gifAbstract:
Pandemic influenza represents a recurring threat to human health. Several times a century, novel influenza A viruses cross over from the animal reservoirs of the world and establish new, dominant lineages in humans. These newly endemic strains may cocirculate with other established lineages or may replace them. Invariably, zoonotic pandemic influenza viruses are more pathogenic than the better-adapted seasonal strain present upon their emergence. This is partly due to differences in primary viral virulence and partly mediated by an enhanced ability to facilitate bacterial superinfections, such as pneumonia ( 1 ). Over time, however, pandemic strains adapt and gradually take on characteristics of seasonal strains with lower virulence and a diminished synergism with bacterial pathogens. Study of this punctuated evolution yields a number of insights into the overall pathogenicity of influenza viruses.
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Influenza A virus life cycle in cells.
Influenza A virus life cycle in cells.
Influenza A virus ecology. The wild-bird reservoir is the source of all zoonotic influenza A viruses. These viruses cross over into humans through intermediate species, such as domestic poultry and swine. Farm animal silhouettes by Otutor, used under License CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/us/); oyster catcher silhouette courtesy of Rachison Alexandra; human silhouettes courtesy of Mackey Creations.
Influenza A virus ecology. The wild-bird reservoir is the source of all zoonotic influenza A viruses. These viruses cross over into humans through intermediate species, such as domestic poultry and swine. Farm animal silhouettes by Otutor, used under License CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/us/); oyster catcher silhouette courtesy of Rachison Alexandra; human silhouettes courtesy of Mackey Creations.
Pandemic timeline. Four major lineages of influenza A virus have established endemicity in humans in the last century. The 1957 and 1968 pandemic viruses were reassortants which included genes from the previously circulating viruses which they replaced. The 1918 and 2009 pandemic strains came directly from animal reservoirs. The seasonal H1N1 lineage which circulated early in the 20th century was replaced in 1957 but reemerged in 1976 and cocirculated for 32 years with seasonal H3N2 strains.
Pandemic timeline. Four major lineages of influenza A virus have established endemicity in humans in the last century. The 1957 and 1968 pandemic viruses were reassortants which included genes from the previously circulating viruses which they replaced. The 1918 and 2009 pandemic strains came directly from animal reservoirs. The seasonal H1N1 lineage which circulated early in the 20th century was replaced in 1957 but reemerged in 1976 and cocirculated for 32 years with seasonal H3N2 strains.
Influenza A virus gene functions
Influenza A virus gene functions