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Generally after each influenza pandemic, the pandemic strain continues to circulate as the cause of seasonal influenza, replacing prior strains. [1] From 1700 to 1889, influenza pandemics occurred about once every 50–60 years. Since then, pandemics have occurred about once every 10–50 years, so they may be getting more frequent over time. [68]
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 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 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.
The main treatment for mild influenza is supportive; rest, fluids, and over-the-counter medicines to alleviate symptoms while the body's own immune system works to recover from infection. Antiviral drugs are recommended for those with severe symptoms, or for those who are at risk of developing complications such as pneumonia. [71] [2]
Cytokines are a normal part of the body's immune response to infection, but their sudden release in large quantities may cause multisystem organ failure and death. [ 1 ] Cytokine storms may be caused by infectious or non-infectious etiologies , especially viral respiratory infections such as H1N1 influenza , H5N1 influenza , SARS-CoV-1 , [ 2 ...
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]
Antigenic shift is contrasted with antigenic drift, which is the natural mutation over time of known strains of influenza (or other things, in a more general sense) which may lead to a loss of immunity, or in vaccine mismatch. Antigenic drift occurs in all types of influenza including influenza A, influenza B and influenza C.