What does AIDS stand for? What causes AIDS?

What does AIDS stand for? What causes AIDS?

AIDS stands for "acquired immunodeficiency syndrome." AIDS is a disease that weakens the immune system to the point where an affected person is vulnerable to a wide range of infections and cancers that result in death if not treated. AIDS is caused by the human immunodeficiency virus (HIV). The virus is spread through contact with infected blood or secretions. At first (stage 1 HIV infection), there is little evidence of harm. Over time, the virus attacks the immune system, focusing on special cells called "CD4 cells" which are important in protecting the body from infections and cancers, and the number of these cells starts to fall (stage 2). Eventually, the CD4 cells fall to a critical level and/or the immune system is weakened so much that it can no longer fight off certain types of infections and cancers. This advanced stage of infection (stage 3) with HIV is called AIDS.

HIV is a very small virus that contains ribonucleic acid (RNA) as its genetic material. (Animal cells, plant cells, bacteria, parasites, and some viruses use deoxyribonucleic acid [DNA] as their primary genetic material rather than RNA.) When HIV infects animal cells, it uses a special enzyme, reverse transcriptase, to turn (transcribe) its RNA into DNA which, in turn, directs the formation of HIV RNA that can be used to form new HIV. This is different from the way human cells reproduce (directly transcribing their DNA into RNA), so HIV is classified as a "retrovirus." When HIV reproduces, it is prone to making small genetic mistakes or mutations, resulting in viruses that vary slightly from each other. This ability to create minor variations allows HIV to evade the body's immunologic defenses, essentially leading to lifelong infection, and has made it difficult to make an effective vaccine. The mutations also allow HIV to become resistant to medications.