H1N1 is a sub-type, of the influenza A virus and is the most common form that infects people. Certain strains of H1N1 are endemic in the human population and cause periodic flu outbreaks. It was an H1N1 flu virus that was responsible for the 1918 flu pandemic that killed 50-100 million people at the end of WWI and into 1919.
The H number in the name refers to the viral hemagglutinin protein, while the N refers to the type of neuraminidase enzyme on the surface of the virus. Both the hemagglutinin and the neuraminidase are involved in the infection process.
It is the H1N1 type that generally causes seasonal influenza worldwide each year and kills tens of thousands of people. Influenza A (H1N1) virus is a subtype of influenza A virus and the most common cause of influenza (flu) in humans. Other strains of H1N1 are endemic in pigs (swine flu) and in birds (avian influenza).
In March 2009, an outbreak of influenza (commonly being called swine flu) in Mexico was confirmed. This novel form of H1N1 flu strain has evolved with genes from human, pig, and bird flu viruses combined. The use of the term swine flu or swineflu is therefore something of a misnomer.
There have been dozens of fatalities there and the incidence of the disease in other countries – US, UK, Spain, Israel, New Zealand is on the increase, the virus having been contracted by people visiting Mexico and returning to these and other countries.The U.S. Centers for Disease Control (CDC) has warned that this could be the first wave of a possible pandemic and the UN and WHO are have put out warnings and advice. We are, at the time of writing in a Phase IV (4) alert as sustained human-to-human transmission of the virus has now been confirmed. Phase VI (6) is the highest level of alert.
At the time of writing the first death from this strain of H1N1 outside Mexico had been reported. A 23-month old baby in Texas.
Other influenza viruses include: H1N1 – H1N2 – H2N2 – H2N3 – H3N1 – H3N2 – H3N8 – H5N1 – H5N2 – H5N3 – H5N8 – H5N9 – H7N1 – H7N2 – H7N3 – H7N4 – H7N7 – H9N2 – H10N7
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