We will surely never know who or how, but we can speculate.
There was a great deal of conjecture in the late 1980’s about Patient Zero, identified as Gaetan Dugas – a Canadian flight attendant who purportedly knowingly infected as many as 250 men a year on both sides of the Atlantic – said to have singlehandedly started the epidemic, but most of this is now largely discredited.
Anyhow, no one ever believed he was the first to be infected. Computer models have estimated that the first human infection occurred about 1930, give or take 20 years. The earliest known infection of an identified human being dates back to 1959, found in a plasma sample taken from an adult male living in Democratic Republic of the Congo.
As to how, most of the loose talk on the street seems to assume sex between a human and a chimp, as the HIV-1 virus is almost identical to a simian virus found in chimpanzees. A human eating a chimp seems just as likely, and some evidence suggests that it may have occurred iatrogenically when chimps were used in developing a polio vaccine for humans.
Below the timeline of HIV/AIDS according to wikipedia:
- Researchers estimate that some time in the early 1900s a form of simian immunodeficiency virus, SIV, was transmitted to humans in central Africa.This particular virus, group M of HIV-1, went on to become the pandemic strain of HIV, though others have been identified.
- Scientists estimate that HIV was circulating in Kinshasa by the 1920s.
- The first known case of HIV in a human occurs in a man who died in the Congo, later (from his preserved blood samples) confirmed as having HIV infection
- Genetic studies of the virus indicate that, in or about 1966, HIV first arrived in the Americas, infecting one person in Haiti. At this time, many Haitians were working in Congo, providing the opportunity for infection.
- The daughter of Arvid Noe dies in January 1976 at 9 years of age.
- Norwegian sailor Arvid Noe dies in April 1976; it is later determined that he contracted HIV/AIDS in Africa during the early 1960s.
- The wife of Arvid Noe dies in December 1976.
- May 18, Lawrence Mass becomes the first journalist in the world to write about the epidemic, in the New York Native, a gay newspaper. A gay tipster overheard his physician mention that some gay men were being treated in intensive-care units in New York City for a strange pneumonia. “Disease Rumors Largely Unfounded” was the headline of Mass’s article. Mass repeated a New York City public-health official’s claims that there was no wave of disease sweeping through the gay community. At this point, however, the Centers for Disease Control (CDC) had been gathering information for about a month on the outbreak that Mass’s source dismissed.
- June 5, The CDC reports a cluster of Pneumocystis pneumonia in five gay men in Los Angeles.
- July 3, An article in The New York Times carries the headline: “Rare Cancer Seen in 41 Homosexuals”. The article describes cases of Kaposi’s sarcoma found in forty-one gay men in New York City and San Francisco.
- July 4, The CDC reports clusters of Kaposi’s sarcoma and Pneumocystis pneumonia among gay men in California and New York City.
- September, “AIDS poster boy” Bobbi Campbell becomes the 16th person in San Francisco diagnosed with Kaposi’s sarcoma.
- October, first reported case in Spain, a 35-year-old gay man. Died shortly after.
- December 12, First known case reported in the United Kingdom.
- One of the first reported patients to have died of AIDS (presumptive diagnosis) in the US is reported in the journal Gastroentereology. Louis Weinstein, the treating physician, wrote that “Immunologic incompetence, related to either disease or therapy, or both … although suspected, could not be proved…”
- By the end of the year, 121 people are known to have died from the disease