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Influenza A virus and influenza B virus circulate in humans and cause seasonal epidemics, and influenza C virus causes a mild infection, primarily in children. Influenza D virus can infect humans but is not known to cause illness. In humans, influenza viruses are primarily transmitted through respiratory droplets from coughing and sneezing.
Influenza viruses are members of the family Orthomyxoviridae. [2] Influenza viruses A, B, C, and D represent the four antigenic types of influenza viruses. [3] Of the four antigenic types, influenza A virus is the most severe, influenza B virus is less severe but can still cause outbreaks, and influenza C virus is usually only associated with minor symptoms.
Influenza viruses A and B are estimated to have diverged from a single ancestor around 4,000 years ago, while the ancestor of influenza viruses A and B and the ancestor of influenza virus C are estimated to have diverged from a common ancestor around 8,000 years ago. [40] Outbreaks of influenza-like disease can be found throughout recorded history.
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The spread of avian influenza in the eastern hemisphere. According to the United Nations FAO, wild water fowl likely plays a role in the avian influenza cycle and could be the initial source for AI viruses, which may be passed on through contact with resident water fowl or domestic poultry, particularly domestic ducks. A newly mutated virus ...
Influenza B virus is almost exclusively a human pathogen, and is less common than influenza A. The only other animal known to be susceptible to influenza B infection is the seal. [47] This type of influenza mutates at a rate 2–3 times lower than type A [48] and consequently is less genetically diverse, with only one influenza B serotype. [26]
Swine influenza (also known as swine flu or pig flu) is a respiratory disease that occurs in pigs that is caused by the Influenza A virus. Influenza viruses that are normally found in swine are known as swine influenza viruses (SIVs). The three main subtypes of SIV that circulate globally are A(H1N1), A(H1N2), and A(H3N2).
Influenza B virus is the only species in the genus Betainfluenzavirus in the virus family Orthomyxoviridae.. Influenza B virus is a negative-sense single-strand RNA virus known only to infect certain mammal species, including humans, ferrets, pigs, and seals.