A zoonosis is an infection or infectious disease that is transmissible from vertebrate animals to people.
The best accepted theory about the origin of HIV is that it is a descendant of a closely related virus, simian immunodeficiency virus (SIV), which infects monkeys. Researchers have known for a long time that certain viruses can pass from animals to humans, a process that is called zoonosis. HIV may have crossed over from chimpanzees as a result of a human killing a chimp and eating it for food.
In 1999, researchers confirmed that tissue from a chimpanzee carried a form of SIV that was nearly identical to an aggressive form of HIV, HIV-1. It appears highly likely chimpanzees were the source of HIV-1, and that the virus at some point crossed species from chimpanzees to humans. We cannot say for sure when the virus first emerged, but it is clear that HIV started to infect humans and became epidemic in the middle of the twentieth century.
There are a number of factors that allowed HIV to move from epidemic to pandemic, but international travel was a key factor. The first person diagnosed with AIDS, and potentially an early source of the HIV epidemic in the United States, called “patient zero,” was a Canadian flight attendant named Gaetan Dugas. He traveled extensively, and analysis of several early cases of AIDS showed that these individuals had either direct or indirect (shared partner) sexual contact with the flight attendant. The early cases were also traced to several different American cities where these infected individuals lived, demonstrating a critical role for air travel in spreading the virus.
Why don't mosquitoes transmit AIDS? The HIV virus does not multiply in mosquitoes. If a mosquito feeds on an HIV-infected human, the virus is treated like food and digested along with the blood meal. If the mosquito resumes feeding on a non-HIV-infected individual, too few particles are transferred to initiate a new infection.
Not long ago, British author Edward Hooper claimed that HIV originated as a product of cross-contamination from an oral polio vaccine administered in Africa in the late 1950s. The vaccine, called “Chat,” was claimed to be derived from chimp kidney cells and was thought to be contaminated with SIV. The vaccine was given to roughly a million people in the Belgian Congo, Rwanda, and Burundi.
On the surface, Hooper's claim seemed to have merit, because the oldest known case of AIDS occurred in a man from Kinshasha near the mouth of the Congo River. His blood was drawn in 1959 and tested positive for HIV. However, the Wistar Institute in Philadelphia, which developed the polio vaccine, came across an old vial containing the original vaccine. After careful analysis, it was proven that the vaccine contained neither HIV nor SIV. In addition, they confirmed that only macaque monkey kidney cells, which cannot be infected with SIV or HIV, were used to make the Chat vaccine. Bottom line, always check your facts, and think twice before throwing old stuff away.
Actor Rock Hudson was the first major public figure known to have died of AIDS. Tennis great Arthur Ashe also died from transfusion-related AIDS. Ryan White, a 13-year-old hemophiliac with AIDS, who eventually died, became famous for his fight to attend school. And basketball superstar Magic Johnson, 10 years after he announced that he was HIV positive, is still living a healthy life with the disease.
A plasma sample taken in 1959 from an adult male living in the Democratic Republic of Congo was found to contain HIV. The virus was found in tissue samples from an African American teenager who died in St. Louis in 1969, and HIV was found in tissue samples from a Norwegian sailor who died around 1976. Many scientists believe that HIV was probably introduced into humans around the 1940s or the early 1950s, although it has been suggested that the first case may actually have occurred in the 1930s.