The biology of HIVa

The biology of HIV

HIV is a virus. A virus is a tiny, relatively simple, nonliving organism, usually made up of little more than a few strands of genetic material and a protein shell. HIV is a virus that infects only people and creates a deficiency in their body's immune system. Viruses similar to HIV affect other animals, including cats and monkeys.

HIV belongs to a family of viruses called retroviruses. Unlike regular viruses, which have DNA (deoxyribonucleic acid) as their genetic material, retroviruses have RNA (ribonucleic acid). Retroviruses also contain an enzyme called reverse transcriptase, which allows the retrovirus's genetic material to imitate the host cell's genetic material.

In comparison to cells and DNA-based viruses, retroviruses mutate (that is, their genetic code changes) very quickly. When retroviruses mutate, a person's immune system often does not have any defenses against the new version of the retrovirus. As a result, retroviruses are more difficult to fight than normal viruses.

Retroviruses mutate more quickly than other viruses because of the way they reproduce. When cells and normal viruses reproduce, an enzyme "proofreads" the resulting genetic material. The equivalent enzyme involved in retroviruses' reproduction—reverse transcriptase—does not proofread the new genes. As a result, new batches of retroviruses are more likely to have errors, or mutations, in their genes than are new batches of normal viruses or cells.

The human immunodeficiency virus also belongs to a subfamily of retroviruses called lentiviruses. Lenti means "slow," so lentiviruses are retroviruses that have a long delay between the time they initially infect a person and the time the person starts to show serious symptoms (Anderson, 1992).