Scientists are not quite sure why the virus, called H5N1, has yet to morph into a strain that can be transmitted between humans. One study found that the avian strain can't bind to human cells. Anotherstudy, released last week, suggested one key mutation is all that is keeping the avian flu out of the human population.
Now two independent research teams have revealed that bird flu virus can bind to human lung cells, but it attaches too deep in the respiratory tract to be coughed up and spread.
Flu viruses are constantly changing and mutating. These changes can happen slowly over time or suddenly.
Antigenic drift is when these changes happen slowly over time. These changes happen often enough that your immune system can’t recognize the flu virus from year to year. That is why you need to get a new flu vaccine each year. The flu vaccine protects you against that season’s three or four most common flu virus strains.
Antigenic shift is when changes happen suddenly. This occurs when two different flu strains infect the same cell and combine. This may create a new flu subtype. Because people have little or no immunity to the new subtype, it can cause a very severe flu epidemic or pandemic.
A virus is a small infectious agent that replicates only inside the living cells of otherorganisms. Viruses can infect all types of life forms, from animals and plants tomicroorganisms, including bacteria and archaea.
Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinckin 1898, about 5,000 viruses have been described in detail, although there are millions of different types. Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity. The study of viruses is known as virology, a sub-speciality of microbiology.
Virus particles (known as virions) consist of two or three parts: i) the genetic material made from either DNA or RNA, long molecules that carry genetic information; ii) a protein coat that protects these genes; and in some cases iii) anenvelope of lipids that surrounds the protein coat when they are outside a cell. The shapes of viruses range from simple helical and icosahedral forms to more complex structures. The average virus is about one one-hundredth the size of the average bacterium. Most viruses are too small to be seen directly with an optical microscope.
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