Influenza A virus H1N1 is a subtype of influenzavirus A and the most common cause of influenza (flu) in humans. Some strains of H1N1 are endemic in humans. This also includes the strain responsible for the 1918 flu pandemic which killed 20-100 million people worldwide.
Less virulent H1N1 strains still exist in the wild today, worldwide, causing a small fraction of all influenza-like illness and a large fraction of all seasonal influenza.Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza).
What Happened To The Virus that Caused Swine Flu?
As the name suggests swine inluenza strain is responsible for the present 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 Mexican influenza,
- North American avian influenza
- Human influenza
- Swine influenza virus typically found in Asia and Europe
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.
Reassortment is the mixing of the genetic material of two similar viruses that are infecting the same cell. In particular, reassortment occurs among influenza viruses, whose genomes consist of eight distinct segments of RNA. These segments act like mini-chromosomes, and each time a flu virus is assembled, it requires one copy of each segment.
Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. The six genes from American swine flu are themselves mixtures of swine flu, bird flu, and human flu viruses.
On June 11, 2009, the WHO declared an H1N1 pandemic, moving the alert level to phase 6.
The virus is contagious and can spread from human to human. Symptoms of swine flu in people are similar to the symptoms of regular human flu such as cough, fever, body aches, sore throat, chills, fatigue and headache.
Swine Flu is a respiratory track infection. This infection is a worldwide virus outbreak that started in Mexico and eventually spread from one country to another continent including China.
