Not really a complete cell but simple nucleic acid (DNA or RNA) encased in protein, a virus must make use of other cells to function and reproduce as a lifeform. Thus it invades cell tissue and interferes with its normal function and genetic behaviour.
Often viruses will kill the host cell and move quickly to invade others. Sometimes they do not kill the cell but live on within it, manipulating its genetic codes in order to reproduce. Such viruses are known as retroviruses and include HIV, which causes AIDS.
Other illnesses and ailments arising from viral infection include the commom cold, chicken pox, measles, warts, influenza, cold sores and genital herpes. The body reacts to their presence by producing special kinds of blood proteins called antibodies. These antibodies remain in the blood after the virus has been beaten and reinfection by the same virus is not possible. Unfortunately, many viruses quickly mutate, rendering the antibodies useless. An example of a rapidly mutating virus is influenza which a person could catch every year. Non-mutating viruses such as mumps are rarely caught twice in a lifetime.
Tags: General health
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