Doctor's Appointment: The True Origins of HIV?

Scientists believe the virus may date back a century or more, and that it spread from chimps in Africa and quickly established itself within the human population.

The disease we know now as acquired immune deficiency syndrome (AIDS) was first described in 1981 among five gay men from Los Angeles, but the virus that causes it has been in existence for much longer.

It's now believed that the virus that causes AIDS, the human immunodeficiency virus (HIV), was transmitted from non-human primates to people as early as 1908 and has been circulating among humans since the 1930s.

In the 25 years since HIV was first described, it has infected 65 million people worldwide and caused 25 million deaths. In countries where it's most common, HIV has reversed improvements in life expectancy and is blamed for setbacks in living standards.

First HIV Transmission to Humans

Exactly how HIV was first transmitted to humans is not definite, but a commonly accepted explanation lies in the African practice of hunting and butchering chimpanzees and other primates and selling them at city markets. Probably a form of the virus not harmful to these non-human primates, simian immunodeficiency virus (SIV), was transferred to humans at such a market in sub-Saharan Africa. Humans probably picked up the virus through direct contact with chimpanzees while hunting or dressing a kill, or by eating uncooked contaminated meat.

The oldest known human tissue sample containing HIV was taken in 1959 from a woman in Kinshasa, (formerly Léopoldville), Zaire. Based on this and other samples, scientists believe HIV-1, the strain responsible for most HIV disease in the world, dates back to a common viral genetic ancestor sometime between 1915 and 1941.

This early first phase of the AIDS pandemic involved several transfers of two kinds of SIV from non-human primates to people. From these two kinds of SIV arose three groups of HIV-1 and several groups of the much less common HIV-2.

The Spread of HIV

It is believed that HIV remained relatively confined to equatorial Africa until the advent of global urbanization and intercontinental travel. This second phase of the AIDS pandemic released HIV to the world. Today, sub-Saharan Africa still bears the brunt of the HIV pandemic. With 10 percent of the world’s population, it is home to 64 percent of those infected with the virus. The Caribbean is second only to sub-Saharan Africa in the proportion of HIV cases compared to the population. In both areas, the virus is spread chiefly by heterosexual contact.

In the United States, the demographic group most closely associated with HIV has been gay men. Of the 27,455 HIV infections diagnosed among male adults and adolescents in 2005, some 71 percent were among men who have sex with men.

The rate of new infections among gay men dropped during the 1980s and 1990s, but has increased since the late 1990s. Paradoxically, one reason for the increase may be the success of new HIV treatments, specifically antiviral therapies introduced in the mid-1990s, which seems to have reduced the fear of HIV and generated a mistaken belief that complying with safer sex practices is not as important as it once was.

Only 5 to 7 percent of adolescent and adult males in the United States identify themselves as gay, so HIV has had a disproportionate impact on this demographic group. But HIV is not exclusive to gay men. Of the estimated 56,300 people with HIV in the United States during 2006, about 27 percent were women, and an estimated 31 percent were infected through heterosexual contact.

Since its discovery, the diverse demographics of HIV infection in the United States and beyond suggest that prevention, treatment, and other outreach efforts must be varied as well.