Influenza Virus

Influenza virus belongs to the Orthomyxoviridae group, which are enveloped, segmented, single-stranded negative sense RNA viruses. The group includes three types of influenza viruses, A, B and C. Type B and C viruses only infect humans, but the type A viruses infect humans, horses, swine, other mammals, and a wide variety of domesticated and wild birds. Human influenza A and B viruses cause seasonal epidemics of disease almost every winter in the United States. The emergence of a new and very different influenza virus to infect people can cause an influenza pandemic. Influenza type C infections cause a mild respiratory illness and are not thought to cause epidemics. Each virus subtype has mutated into a variety of strains with differing pathogenic profiles; some are pathogenic to one species but not others, some are pathogenic to multiple species.