H1N1 influenza
Enlarge text Shrink text- Work cat.: 2009 H1N1 Flu (Swine Flu) [CDC website, Nov. 2, 2009](2009 H1N1, novel influenza A, aka swine flu; new influenza virus causing illness in people; first detected in people in U.S. April 2009; spreading from person-to-person worldwide, probably in much the same way that regular seasonal influenza viruses spread; World Health Organization (WHO) signaled a pandemic of 2009 H1N1 flu was underway on June 11, 2009; originally referred to as swine flu because laboratory testing showed many genes in this new virus were very similar to influenza viruses that normally occur in pigs (swine) in North America; further study has shown that this new virus is very different from what normally circulates in North American pigs--has two genes from flu viruses that normally circulate in pigs in Europe and Asia and bird (avian) genes and human genes; scientists call this a "quadruple reassortant" virus; new flu virus of swine origin that first caused illness in Mexico and the United States in March & April, 2009)
- Infection control guidelines for healthcare workers for novel influenza A, H1N1, 2009(novel influenza A (H1N1) virus; appears behave similarly to seasonal influenza in terms of severity of illness & transmission of infection)
- Novel H1N1 Continues to Wallop Younger U.S. Population [Science insider, Oct. 20, 2009](novel H1N1 virus; people under 65 suffer the bulk of hospitalizations & deaths from the virus, exactly the opposite pattern seen w/seasonal influenza which primarily causes severe disease in the elderly)
Influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus (IAV). Some human-adapted strains of H1N1 are endemic in humans and are one cause of seasonal influenza (flu). Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza). Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope; for example, "H1N1" designates an IAV subtype that has a type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein. All subtypes of IAV share a negative-sense, segmented RNA genome. Under rare circumstances, one strain of the virus can acquire genetic material through genetic reassortment from a different strain and thus evolve to acquire new characteristics, enabling it to evade host immunity and occasionally to jump from one species of host to another. Major outbreaks of H1N1 strains in humans include the 1918 Spanish flu pandemic, the 1977 Russian flu pandemic and the 2009 swine flu pandemic, all of which were caused by strains of A(H1N1) virus which are believed to have undergone genetic reassortment. Each year, three influenza strains are chosen for inclusion in the forthcoming year's seasonal flu vaccination by the Global Influenza Surveillance and Response System of the World Health Organization (WHO). Since 1999, every annual formulation has included one strain of A/H1N1 as well as two other influenza strains - together representing strains thought most likely to cause significant human suffering in the coming season.
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