How Virus Survives

Viruses are obligate intracellular parasites which infects living cells for their own nourishment. They behave as both living and non living organisms. Lets discuss how viruses survives inside or out side of the living cells.

• Outside a Host cell

Virus does not have cellular , cellular or spore forms as parasites. When there is no host or when there are unfavourable conditions, outside the cells viruses may form crystals, e.g., Tobacco mosaic virus. Some remain in saliva, in respiratory droplets, e.g, Influenza A virus, measles virus, Vermicelli zoster virus (chicken pox), in respiratory aerosol, e.g., small pox virus, in the feces e.g., adenoviruses.

• Inside a Host Cell 

Viruses surround the host immune response by:

1. Blocking complement activation, e.g., vaccine or using complement receptor to enter B lymphocytes.
2. Inhibiting interferon induced antiviral responses.
3. Blocking production of cytokines or response to cytokines e.g., cowpox.
4. Suppressing major histocompatibility complex.
5. Reducing B-cell activation
6. Changing their own genetic constitution so rapidly that vaccines or antibodies of host against them become ineffective.