Virus may be seen only with the help of electronic microscope. The vast majority of doctors meet viruses and electronic microscopes only on images in clever medical books. Diseases caused by viruses have so specific symptoms that it makes no use of electronic microscope and images because everything is clear.
The essential and most significant biological peculiarity of any virus is that it is unable to multiply without cells of other organisms. Virus enters a particular cell and this infected cell transforms into a factory of virus production.
It is clear that cell cannot work for both virus and body and thus it cannot perform its major function and here appear absolutely specific symptoms of the disease. Major feature of the virus is its selectivity. Virus cannot live in any cell, it needs a proper one which will work for it.
For example, infectious hepatitis virus may live and multiply only in liver cells. Epidemic parotitis virus (mumps) prefers cells of salivary gland, influenza virus – cells of mucous membrane of bronchi and tracheae, encephalitis virus – cells of cerebrum. Each virus may be associated with particular cells and tissues of human body which virus damages.
Virus selectivity is observed not only in damages of particular cells but also in the ability to cause particular diseases in particular biologic species. Measles virus may find necessary cells in human body and is not dangerous for a cat. Virus of hardpad is not dangerous for a human.
These are not common rules. Particular cells of different mammals are analogous with each other and some viruses cause one and the same disease in different animals, for example, rabies virus. The ability of some viruses to affect only particular biological species has a great significance.
No comments:
Post a Comment