Type a Influenza Virus
Influenza: a virus that replicates, mutates, spreads among species, and the cause of the recent H1N1 scare is definitely an apparent danger to humans today.
Type A influenza is an RNA virus that ‘reproduces’ through replication. The virus particles are surrounded by hemagglutinin (HA) and neuraminidase (NA) – both are structural glycoproteins attached to the virus’s outside lipid bi-layer. HA serves its function in helping the virus to bind to the sialic acid receptors located on the human cell. Then, through endocytosis, the virus enters the cell and makes its way to the host cell’s nucleus. Through transcription, the virus then creates copies of mRNA (messenger RNA) and uses them to translate new viral proteins (replication) – essentially creating new virus particles. These particles then attempt to escape the cell but HA again binds to the sialic acid receptors – preventing this. The glycoprotein NA then plays its role in ‘splitting’ the virus particles from the receptors – allowing its escape and therefore infection other cells.
The human immune system usually responds to the spread of the virus, unless the virus evades detection. This is possible is through the modification of the virus’s HA and NA exterior glycoproteins. The virus then avoids detection because the antibodies released will be ineffective in binding to the new antigenic sites on the modified HA and NA proteins – ultimately the host doesn’t recognize the modified virus. The virus achieves such mutations due to the lack of enzymes that correct errors made on the viral genome during replication. The errors are therefore uncorrected, hence the virus mutates rapidly. This process is known as antigenic drift. But, the virus is more feared for its significant mutation due to the process of antigenic shift. In this process, the antigenic sites (HA and NA) mutate more rapidly and can even be completely replaced with new variations of the glycoproteins. The human body then cannot identify the virus, and so the new strain created can become lethal, and especially dangerous if contagious.
The virus originates from wild aquatic birds. It doesn’t affect them as it’s found in their intestinal tract, and spreads through water contaminated from their feces. Mammals, especially swine, and domestic poultry exposed to such water are then infected with the virus. Swine serve as good mediums (for the virus) between humans and birds as they are able to be infected with both human and avian types of the virus – meaning they have receptors for both sub-strains. The two sub-strains can then undergo antigenic shift far easier within swine to produce a new, possibly lethal strain. The virus then spreads through the human consumption of their meat products.
H1N1 (a deadly and infectious strain) caused the Canadian government, and some other countries, to make the virus as public as possible and urged the public to get their free vaccinations. Some believe it was an over-reaction, my opinion is rather be safe than sorry. I think the quick reaction time, and publically available vaccinations may have prevented H1N1 from causing a disaster.
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