How new strain of influenza viruses evolve ?

Saturday, September 5, 2009

Whenever a new version of virus evolves , there's a chance that it'll become pandemic. Its because human does not have immuno resistance against that new strain. However, the interesting Ques. is how these new strains evolve?

New strain of virus ( like " Nobel H1N1" ) can be emerged via two basic processes.They r -

1. Antigenic Shift

2. Antigenic Drift

Antigenic shift is the process by which at least two different strains of a virus (or different viruses), especially influenza, combine to form a new subtype having a mixture of the surface antigens of the two original strains. The term antigenic shiftis more often applied specifically (but is not limited) to the influenza. Antigenetic shift is a specific case of reassortment or viral shift that confers a phenotypic change.

Genomes of influenza virus consist of 8 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. If a single host (a human, a chicken, or other animal) is infected by two different strains of the influenza virus, then it is possible that new assembled viral particles will be created from segments whose origin is mixed, some coming from one strain and some coming from another. The new reassortant strain will share properties of both of its parental lineages.

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Another term Antigenic drift is completely diferent and should not be confused with Antigenic shift. Random mutations in the genes of a virus drives antigenic drift that changes the antigens of the virus. As these changes accumulate it may help the virus to evade the immune system since antigens are what the immune system recognizes.

Thus a new strain can evolve by the genetic changes in viral genome... !

Reference:

http://en.wikipedia.org/wiki/Antigenic_drift

http://en.wikipedia.org/wiki/Antigenic_shift

Nobel H1N1 Swine influenza virus in brief

Wednesday, September 2, 2009

Introduction

Swine influenza virus is actually a virus of pigs and its commom thoughout pig population worldwide. Transmission of this virus from pigs to human is rare and it usually can not pass from human to human. But early in this year (2009), a new strain of influenza virus is found in human (a zoonosis) which was thought to be come from pigs and its capable of spreading from human to human. This virus is classified under influenza A, subtype H1N1, generally known as the swine flu virus or "nobel H1N1"

What does H1N1 mean actually?

There r 3 genera of influenza virus that cause human flu. Those r Influenza A, B and C. Influeza A is the most common cause of seasonal flu,but also there are some other strain of influenza A those are endemic in pigs and birds. 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. 3 H and 2 N subtypes r common in human.

Origin

The new strain was initially described as an apparent reassortment (mixing of the genetic materials of two or more viruses) of at least four strains of influenza A virus subtype H1N1, including one strain endemic in humans, one endemic in birds, and two endemic in swine. Subsequent analysis suggested it was a reassortment of just two strains, both found in swine. Although initial reports identified the new strain as swine influenza (i.e., a zoonosis originating in swine), its origin is still not clear.

Who r in risk?

Those who have lower immuno resistance ,such as children, HIV positives r very much susceptible for this virus.The U.S. Centers for Disease Control and Prevention (CDC) noted that although this was a very serious virus, cases worldwide were usually mild, and most hospitalizations and deaths had been of persons that also had underlying conditions such as asthma, diabetes, obesity, heart disease, or a weakened immune system.

Vaccination

Vaccines are available for different kinds of swine flu. Although the current trivalent influenza vaccine is unlikely to provide protection against the new 2009 H1N1 strain,vaccines against the new strain are being developed and could be ready as early as November 2009. Besides, ayurvedic experts said, tulsi pata( a herb) provide a little bit resistance against swine flu as well as any other seasonal flu. But if the new virus mutated futher ,it could become more virulent and less susceptible to any new vaccines.

reference:

http://en.wikipedia.org/wiki/2009_flu_pandemic

Cancer cells and embryonic stem cells r immortal. How they escape death ?

Monday, June 15, 2009

In 1961 ,Dr, Leonard Hayflick discovered that when cells are taken from the body and grown in tissue culture on a laboratory dish, there is a limit to how long the cell line lives . After about 50 (the num varies with the kind of tissue) divisions, the aging cell line dies. Its known as Hayflick limit. This Hayflick limit has puzzled developmental biologists for decades. What causes the cells, after so many successful divisions, to abruptly break down ? How does a cell know its time is up?

But scientist now know all the answers !!!

The secret to immortality proved to be a short tag of DNA attached on the tips of the cell's chromosomes,known as telomere. This segment of DNA plays a key role in cell division. The telomere provides a place for the cell's DNA-copying machinery to latch onto the chromosome when the time comes for the chromosomal DNA to be copied into daughter chromosomes. However, every time the machinery attaches, the short bit of the telomere where the machinery sits down on the DNA is not itself copied, so the telomere gets a little shorter each time the cell divides. When the telomere reaches a minimal length after some 50 divisions, the cell can no longer replicate its DNA and lapses into senescence.

So, why Cancer and ESC cells are immortal ?

All cells possess a gene, known as the telomerase gene, which can add DNA back to the tip of telomeres. In almost all cells this gene is turned off early in development. If somehow, this gene is turned on then the cell become a cancer cell.

Embryonic Stem Cells also have the telomerase activity. But when they differentiate into other specialized cells they lose their telomerase activity ,as well as immortality. A few, however, are set aside, protected from the influences that trigger differentiation and shutting down of the telomerase gene. Called germ line cells, these embryonic stem cells have a fully functional telomerase gene and continue to divide, producing eggs and sperm that in their turn produce more stem cells in the next generation.

reference :

http://txtwriter.com/onscience/index.html