Theories on the origin of Aids have sparked considerable interest and controversy since the beginning of the epidemic. Some people, in trying to identify where Aids originated, may try and use the debate to blame particular groups of individuals or certain lifestyles for the epidemic. The history of our interaction with the HI virus, and especially the rise and fall of many prevention initiatives, are sometimes more useful to help us to understand our own behaviour. The following is the story of the beginning of the HI virus.
The first cases of Aids occurred in the USA in 1981, but they provide little information about the source of the disease. There is now clear evidence that the disease Aids is caused by the HI virus. But where does HIV come from?
What type of virus is HIV?
HIV is part of a family or group of viruses called lentiviruses. These viruses are known to be slow to cause disease. Lentiviruses other than HIV have been found in a wide range of nonhuman primates. HIV is related to the simian (monkey) immunodeficiency virus (SIV).
So where did HIV come from? Did HIV come from SIV?
It is now generally accepted that HIV is a descendant of the simian (monkey) immunodeficiency virus (SIV). Certain SIVs bear a very close resemblance to HIV-1 and HIV-2, the two types of HIV. For example, HIV-2 corresponds to an SIV found in the Sooty Mangabey (SIVsm), sometimes known as the Green Monkey, which is indigenous to western Africa.
The more virulent strain of HIV, namely HIV-1, was until very recently more difficult to trace. In 1999 the research of Beatrice Hahn and her team from the University of Alabama confirmed that the chimpanzee viruses from West Central Africa were most closely related to HIV-1. They had studied frozen tissue from a chimpanzee and found that the simian virus it carried (SIVcpz) was almost identical to HIV-1. The chimpanzee came from a sub-group of chimpanzees common in West Central Africa.
Hahn concluded that the West Central African chimpanzee was the natural host and reservoir for existing HIV-1 strains. It is unclear whether chimpanzees continue to serve as reservoirs for the virus. The researchers claim that these chimpanzees were the source of HIV-1, and that the virus at some point crossed species from chimpanzees to humans. However, it was not necessarily clear that chimpanzees were the original reservoir for HIV-1 because chimpanzees are only rarely infected with SIVcpz.
Is there any evidence of when the transfer took place?
During the last few years it has become possible not only to determine whether HIV is present in a blood or plasma sample, but also to determine the particular subtype of the virus. Studying the subtype of virus of some of the earliest known instances of HIV infection can help to provide clues about the time of origin and the subsequent evolution of HIV in humans.
Three of the earliest known instances of HIV infection are as follows:
- A plasma sample taken in 1959 from an adult male living in what is now the Democratic Republic of Congo.
- HIV found in tissue samples from an African-American teenager who died in St. Louis in 1969.
- HIV found in tissue samples from a Norwegian sailor who died around 1976.
Analysis in 1998 of the plasma sample from 1959 was interpreted as suggesting that HIV-1 was introduced to humans around the 1940s or the early 1950s, which was earlier than had previously been suggested. Other scientists have suggested that it could have been even longer, perhaps more than a hundred years ago.
In January 2000, the results of a new study presented at the Seventh Conference on Retroviruses and Opportunistic Infections suggested that the first case of HIV infection occurred around 1930 in West Africa. The study was carried out by Dr Bette Korber of the Los Alamos National Laboratory. The estimate of 1930 (which does have a 20-year margin of error) is based on a complicated computer model of HIV’s evolution.
Is it known where HIV entered the population?
Many people now assume that because HIV has apparently developed from a form of SIV found in a type of chimpanzee in West Africa, it was actually in West Africa that HIV first emerged in humans. It is then presumed that HIV spread from there to the rest of the world.
We will probably never know exactly when and where the virus first emerged. What is clear, however, is that sometime in the middle of the 20th century, HIV infection in humans developed around the world into the epidemic disease that we now refer to as Aids.
What caused the epidemic to spread so quickly?
There are a number of factors that may have contributed to the sudden spread, including international travel, the blood industry and widespread drug use.
International travel. The role of international travel in the spread of HIV was highlighted by the case of ‘Patient Zero’. Patient Zero was a Canadian flight attendant, Gaetan Dugas, who travelled extensively worldwide. Analysis of several of the early cases of Aids showed that the infected individuals were either direct or indirect sexual contacts of the flight attendant. These cases could be traced to several different American cities, demonstrating the role of international travel in spreading the virus. It also suggested that the disease was probably the consequence of a single transmissible agent.
The blood industry. As blood transfusions became a routine part of medical practice, the industry involved in meeting this increased demand for blood grew. In some countries, such as the USA, paid donors were used, including intravenous drug users. This blood was then sent worldwide. Also, in the late 1960s haemophiliacs began to benefit from the blood clotting properties of a product called Factor VIII. However, to produce the coagulant, blood from thousands of individual donors had to be pooled. Factor VIII was then distributed worldwide making it likely that haemophiliacs could become exposed to new infections.
Drug use. In the 1970s, following the Vietnam War and other conflicts in the Middle East, there was an increase in the availability of heroin. This increased availability, together with the development of disposable plastic syringes and the establishment of ‘shooting galleries’ where people could buy drugs and rent equipment, provided another route through which the virus could be passed on.
What other theories have there been about the origin of HIV?
A number of conspiracy theories are put forward about the origin of HIV. Some people have suggested that HIV was manufactured by the American Central Intelligence Agency (the CIA), while others believe that HIV was genetically engineered.