| Influenza A virus subtype H1N1 | |
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Virus classification 
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| (unranked): | Virus |
| Realm: | Riboviria |
| Kingdom: | Orthornavirae |
| Phylum: | Negarnaviricota |
| Class: | Insthoviricetes |
| Order: | Articulavirales |
| Family: | Orthomyxoviridae |
| Genus: | Alphainfluenzavirus |
| Species: | Influenza A virus |
| Serotype: | Influenza A virus subtype H1N1 |
| Strains | |
| Influenza (Flu) |
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virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of Influenza A virus. Well known outbreaks of H1N1 strains in humans include the 2009 swine flu pandemic, as well as the 1918 flu pandemic. It is an orthomyxovirus that contains the glycoproteins haemagglutinin and neuraminidase. For this reason, they are described as H1N1, H1N2 etc. depending on the type of H or N antigens they express with metabolic synergy. Hemagglutinin causes red blood cells to clump together and binds the virus to the infected cell. Neuraminidase is a type of glycoside hydrolase enzyme which helps to move the virus particles through the infected cell and assist in budding from the host cells.[1]
Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza, for instance in 2004–2005.[2] Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza). Its size is 80 to 120 nm in diameter.[3] Swine influenzaSwine 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 known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H3N1, H3N2 and H2N3. Pigs can also become infected with the H4N6 and H9N2 subtypes.[citation needed] Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu or a variant virus. People with regular exposure to pigs are at increased risk of swine flu infection. Properly cooking the meat of an infected animal removes the risk of infection. Pigs experimentally infected with the strain of swine flu that caused the human pandemic of 2009–10 showed clinical signs of flu within four days, and the virus spread to other uninfected pigs housed with the infected ones.[4] Notable incidents1918–1919 Spanish fluThe Spanish flu was an unusually severe and deadly strain of H1N1[5] avian influenza, a viral infectious disease, that killed some 17[6] to 50 or more million people worldwide over about a year in 1918 and 1919. It was one of the deadliest pandemics in human history. The 1918 flu caused an abnormally high number of deaths, possibly due to it provoking a cytokine storm in the body.[7][8] (The current H5N1 bird flu, also an Influenza A virus, has a similar effect.)[9] After the Spanish flu infected lung cells it frequently led to overstimulation of the immune system via release of cytokines (a protein that invokes the immune response) into the lung tissue. This leads to extensive leukocyte migration towards the lungs, resulting in the destruction of lung cells and secretion of blood and mucus into the alveoli and airways. This makes it difficult for the patient to breathe and can result in suffocation. In contrast to other pandemics, which mostly kill the old and the very young, the 1918 pandemic killed unusual numbers of young adults, which may have been due to their healthy immune systems mounting a too-strong and damaging response to the infection.[10] The term "Spanish" flu was coined because Spain was at the time the only European country where the press were printing reports of the outbreak, which had killed thousands in the armies fighting World War I (1914–1918). Other countries suppressed Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza, for instance in 2004–2005.[2] Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza). Its size is 80 to 120 nm in diameter.[3] 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 known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H3N1, H3N2 and H2N3. Pigs can also become infected with the H4N6 and H9N2 subtypes.[citation needed] Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu or a variant virus. People with regular exposure to pigs are at increased risk of swine flu infection. Properly cooking the meat of an infected animal removes the risk of infection. Pigs experimentally infected with the strain of swine flu that caused the human pandemic of 2009–10 showed clinical signs of flu within four days, and the virus spread to other uninfected pigs housed with the infected ones.[4] Notable incidents1918–1919 Spanish fluThe Spanish flu was an unusually severe and deadly strain of H1N1[5] avian influenza, a viral infectious disease, that killed some 17[6] to 50 or more million people worldwide over about a year in 1918 and 1919. It was one of the deadliest pandemics in human history. The 1918 flu caused an abnormally high number of deaths, possibly due to it provoking a cytokine storm in the body.[7][8] (The current H5N1 bird flu, also an Influenza A virus, has a similar effect.)[9] After the Spanish flu infected lung cells it frequently led to overstimulation of the zoonotic swine flu or a variant virus. People with regular exposure to pigs are at increased risk of swine flu infection. Properly cooking the meat of an infected animal removes the risk of infection. Pigs experimentally infected with the strain of swine flu that caused the human pandemic of 2009–10 showed clinical signs of flu within four days, and the virus spread to other uninfected pigs housed with the infected ones.[4] The Spanish flu was an unusually severe and deadly strain of H1N1[5] avian influenza, a viral infectious disease, that killed some 17[6] to 50 or more million people worldwide over about a year in 1918 and 1919. It was one of the deadliest pandemics in human history. The 1918 flu caused an abnormally high number of deaths, possibly due to it provoking a cytokine storm in the body.[7][8] (The current H5N1 bird flu, also an Influenza A virus, has a similar effect.)[9] After the Spanish flu infected lung cells it frequently led to overstimulation of the immune system via release of cytokines (a protein that invokes the immune respon The 1918 flu caused an abnormally high number of deaths, possibly due to it provoking a cytokine storm in the body.[7][8] (The current H5N1 bird flu, also an Influenza A virus, has a similar effect.)[9] After the Spanish flu infected lung cells it frequently led to overstimulation of the immune system via release of cytokines (a protein that invokes the immune response) into the lung tissue. This leads to extensive leukocyte migration towards the lungs, resulting in the destruction of lung cells and secretion of blood and mucus into the alveoli and airways. This makes it difficult for the patient to breathe and can result in suffocation. In contrast to other pandemics, which mostly kill the old and the very young, the 1918 pandemic killed unusual numbers of young adults, which may have been due to their healthy immune systems mounting a too-strong and damaging response to the infection.[10] The term "Spanish" flu was coined because Spain was at the time the only European country where the press were printing reports of the outbreak, which had killed thousands in the armies fighting World War I (1914–1918). Other countries suppressed the news in order to protect morale.[11] In 1976, a novel swine influenza A (H1N1) caused severe respiratory illness in 13 soldiers, with one death at Fort Dix, New Jersey. The virus was detected only from 19 January to 9 February and did not spread beyond Fort Dix.[12] Retrospective serologic testing subsequently demonstrated that up to 230 soldiers had been infected with the novel virus, which was an H1N1 strain. The cause of the outbreak is still unknown and no exposure to pigs was identified.[13] 1977–1978 Russian flu |