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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.
The genetic structure of H5N1, a highly pathogenic avian influenza virus (influenza A virus subtype H5N1), is characterized by a segmented RNA genome consisting of eight gene segments that encode for various viral proteins essential for replication, host adaptation, and immune evasion.
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]
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.
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 A virus subtype H3N2 (A/H3N2) is a subtype of influenza A virus (IAV). Some human-adapted strains of A/H3N2 are endemic in humans and are one cause of seasonal influenza (flu). [ 1 ] Other strains of H1N1 are endemic in pigs ( swine influenza ) and in birds ( avian influenza ). [ 2 ]
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 .
Influenza A viruses differ by comprising multiple ribonucleoproteins, the viral NP protein organizes the RNA into a helical structure. The size is also different; the tobacco mosaic virus has a 16.33 protein subunits per helical turn, [22] while the influenza A virus has a 28 amino acid tail loop. [25]