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• Influenza A viruses infect a wide variety of mammals, including man, horses, pigs, ferrets and birds.

• Influenza A viruses are a major human pathogen, associated with epidemics and pandemics.

• Influenza B viruses infect humans only and cause disease, but generally not a severe as A types.

• Influenza B viruses are believed to be epidemiologically important - reassortment with type A leads to epidemics.

• Influenza C viruses infect humans only, but are not believed to cause disease.