"What should I know about Influenza A"
Influenza A is the most common type of the influenza virus. Some strains of the Influenza A virus are endemic in humans and cause a small fraction of the influenza illness as well as the majority of the seasonal flu illness.
IN 2006, the influenza A virus was to be the cause of nearly half or all the human flu infections. Influenza A not only infects humans, it has been found to infect pigs as well as birds.
In June 2009, the World Health Organization declared that the Influenza A virus was the strain of the virus that was responsible for the 2009 flu pandemic.
The influenza A virus strain is categorized according to the two proteins found on their surface: hemagglutnin and neuraminidase. In fact all strains of the flu contain these two proteins -- but their structures vary which is why there are many different strains of the common influenza virus. And there are so many different kinds of the influenza virus because they constantly undergo rapid genetic mutations.
Influenza A virus strains are assigned a hemagglutinin (H) number and a neuraminidase (N) number based on the forms each of these proteins make on the surface of the virus. In total there are sixteen (H) and nine (N) subtypes found in other species. But as of now, only (H) 1, 2 and 3 and (N) 1, 2, and 3 are found in humans.
But as long as genetic mutations continue to occur on the surface of these viruses, there is always a chance that these will start to infect humans.