Influenza A virus subtype H1N1

 Influenza A virus subtype H1N1

 A preliminary report

Influenza A H1N1 virus is a subtype of influenzavirus A and the most common cause of influenza (flu) in humans. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a large fraction of all seasonal influenza. H1N1 strains caused roughly half of all human flu infections in 2006.
 Other strains of H1N1 are endemic in pigs " swine influenza" and in birds "avian influenza".

In June 2009, World Health Organization declared that flu due to a new strain of swine-origin H1N1 was responsible for the 2009 flu pandemic. This strain is often called "swine flu" by the public media.

See WHO declares influenza A (H1N1) pandemic

Dr Margaret Chan speaks to the media at the agency's headquarters in Geneva, on the 11th of June 2009. On the basis of available evidence and expert assessments of the evidence, the scientific cri... 

Designation of the disease " Nomenclature ": --

There are more than one reason for the designation of the disease this name
Influenza A virus strains are categorized according to two proteins found on the surface of the virus: hemagglutinin (H) and neuraminidase (N). All influenza A viruses contain hemagglutinin and neuraminidase, but the structures of these proteins differ from strain to strain, due to rapid genetic mutation in the viral genome.

Influenza A virus strains are assigned an H number and an N number based on which forms of these two proteins the strain contains. There are 16 H and 9 N subtypes known in birds, but only H 1, 2 and 3, and N 1 and 2 are commonly found in humans.

Russia and Spain: --

Her disease history with two states, Russia and Spain.

Russia was the epidemic of H1N1 avian influenza between 1977 to 1978. And hit the infection significantly below the age of 23 years, and therefore to acquire the older of immunity against the virus infection by a similar period from 1947 to 1957. This epidemic is not considered a pandemic as a real limit myself to a specific age group.
Likewise, the Spain of this disease and the virus.
The Spanish flu, also known as La Gripe Española, or La Pesadilla, was an unusually severe and deadly strain of avian influenza, a viral infectious disease, that killed some 50 million to 100 million people worldwide over about a year in 1918 and 1919. It is thought to be one of the most deadly pandemics in human history.
 It was caused by the H1N1 type of influenza virus.

The 1918 flu caused an unusual number of deaths, possibly due to it causing a cytokine storm in the body. (The current H5N1 bird flu, also an Influenza A virus, has a similar effect.)
 The Spanish flu virus infected lung cells, leading to overstimulation of the immune system via release of cytokines into the lung tissue.
 This leads to extensive leukocyte migration towards the lungs, causing destruction of lung tissue and secretion of liquid into the organ. This makes it difficult for the patient to breathe. 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

   

The virus is spreading again:

At the beginning of the disease began to spread again
In the 2009 flu pandemic, the virus isolated from patients in the United States was found to be made up of genetic elements from four different flu viruses - North American swine influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe - "an unusually mongrelised mix of genetic sequences."
 This new strain appears to be a result of reassortment of human influenza and swine influenza viruses, in all four different strains of subtype H1N1.

   

Information from the World Health Organization

Wikipedia