Acquired Immune Deficiency Syndrome (AIDS)
Human immunodeficiency virus (HIV) is contracted through sexual contact via anal, oral, or vaginal intercourse; blood exchange; shared intravenous syringes; or from mother to child during pregnancy, labor, delivery, or breast-feeding. It originated in primates but ultimately transmitted to humans. The first cases were discovered in Africa in 1950s and 1960s, and the disease spread rapidly throughout the globe, affecting more than 36 million people by 2001.
HIV causes progressive failure of the immune system, making the body far more susceptible to infections and cancer. Although some antiretroviral drugs reduce the mortality and morbidity of the infection, there is no cure for HIV, and it's high genetic variability makes treatment options limited. Most untreated HIV victims ultimately develop acquired immunodeficiency syndrome (AIDS).
As AIDS greatly compromises the immune system, patients die not from AIDS itself, but from opportunistic infections or malignancies, such as the common cold virus or pneumonia. The length of time for HIV to develop into AIDS varies but, if left untreated, HIV will transition to AIDS approximately 10 years after infection.
Most experts agree that HIV is a descendent of the simian immunodeficiency virus (SIV), which initially only affected primates but, after mutating, was able to be transmitted to humans, likely as a result of humans killing monkeys and eating their flesh. After being acquired by humans, and once the disease was regularly transmitted from person to person, it became known as a human virus. HIV was transmitted throughout the world when travel out of Africa to other parts of the world became accessible. Roads and river transportation allowed for easier and quicker travel to industrialized parts of the world. The syndrome was finally regarded as a clinical virus in 1981 and named in 1986.
There are two types of HIV: Type 1, which can be broken down into several subgroups based on location, and type 2, which seems to be less easy to transmit. Both are contracted through the exchange of bodily fluids, and both can cause clinically indistinguishable AIDS, the final, life-threatening stage of HIV.
- HIV-1: HIV-1 is the more predominant form of the virus and is split into several subgroups. The dominant strain, group M, was found in chimpanzees and monkeys living in West Africa and is responsible for the AIDS pandemic.
- HIV-2: HIV-2 is found primarily in West Africa and is not as transmittable or virulent as HIV-1, but it causes AIDS more frequently than type 1. The period between initial infection and illness is longer in HIV-2 cases.
Written by: The Healthline Editorial Team
Medically reviewed by Jennifer Monti, MD, MPH