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Influenza A virus structure. The influenzavirus virion is pleomorphic; the viral envelope can occur in spherical and filamentous forms. In general, the virus's morphology is ellipsoidal with particles 100–120 nm in diameter, or filamentous with particles 80–100 nm in diameter and up to 20 μm long. [5]
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.
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.
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.
The influenza viruses are members of the family Orthomyxoviridae. [1] Influenza viruses A, B, C, and D represent the four antigenic types of influenza viruses. [4] 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. [5]
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 hemagglutinin (HA) or haemagglutinin [p] (British English) is a homotrimeric glycoprotein found on the surface of influenza viruses and is integral to its infectivity. Hemagglutinin is a class I fusion protein , [ 1 ] [ 2 ] having multifunctional activity as both an attachment factor and membrane fusion protein .
3D model of the flu virion. (M2 labeled in white.) The Matrix-2 (M2) protein is a proton-selective viroporin, integral in the viral envelope of the influenza A virus. The channel itself is a homotetramer (consists of four identical M2 units), where the units are helices stabilized by two disulfide bonds, and is activated by low pH.