Genes Involved in the Restriction of Replication of Avian Influenza A Viruses in Primates
The influenza viruses are enveloped viruses with a segmented genome of eight negative-sense stranded RNA segments (Murphy and Webster, 1989). Influenza viruses are classified into three types, A, B, and C, based on differences in the antigenicity of their nucleoprotein and matrix proteins. Influenza A viruses infect a variety of animal species, including swine, horses, marine mammals, birds, and humans. In humans, influenza A viruses cause respiratory infections with significant morbidity and mortality especially in the elderly and in individuals with chronic pulmonary or cardiac disease. The epidemiology of these infections is complex but is characterized by periodic worldwide pandemics with high attack rates. Such pandemics are associated with changes in the major protective antigens of the virus, the hemagglutinin and neuraminidase. This type of genetic change in influenza viruses is referred to as antigenic shift. The most recent pandemics of influenza A in humans occurred in 1957, when viruses of the HIN1 subtype were replaced by the H2N2 subtype, and in 1968, when the H2N2 virus was replaced by the H3N2 virus (Fig. 1). Since 1977, both the H1N1 and H3N2 subtypes of influenza A virus have cocirculated in humans.
KeywordsInfluenza Virus Avian Influenza Avian Influenza Virus Squirrel Monkey Human Influenza
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