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Influenza A viruses are further classified, based on the viral surface proteins hemagglutinin (HA or H) and neuraminidase (NA or N). 18 HA subtypes (or serotypes) and 11 NA subtypes of influenza A virus have been isolated in nature. Among these, the HA subtype 1-16 and NA subtype 1-9 are found in wild waterfowl and shorebirds and the HA ...
Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses.Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue.
The subtypes of influenza A virus are estimated to have diverged 2,000 years ago. 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.
To unambiguously describe a specific isolate of virus, researchers use the Influenza virus nomenclature, [21] which describes, among other things, the subtype, year, and place of collection. Some examples include: [22] A/Rio de Janeiro/62434/2021 (H3N2). [22] The starting A indicates that the virus is an influenza A virus.
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes the disease avian influenza (often referred to as "bird flu"). It is enzootic (maintained in the population) in many bird populations, and also panzootic (affecting animals of many species over a wide area). [ 1 ]
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.
Antigenic drift occurs in both influenza A and influenza B viruses. (Confusion can arise with two very similar terms, antigenic shift and genetic drift . Antigenic shift is a closely related process; it refers to the more dramatic changes in the virus's surface proteins when the genetic material from two or more viruses mix together.
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).