Where Did HIV Come From?
What Is HIV?
HIV, or human immunodeficiency virus, is the causative agent of AIDS (acquired immune deficiency syndrome). There are actually two types of HIV; HIV-1 and HIV-2. HIV-1 is the dominant virus worldwide, whereas HIV-2 is largely confined to West African countries and those with links to this area such as France and Portugal.
HIV-2 is separated into eight groups, A-H, with group A being the most prevalent worldwide. Only groups A and B have been successfully transmitted between humans- the rest have been isolated cases with “dead end” viruses. HIV-1 is divided into 4 groups; M, N, O and P. M, which has been responsible for the majority of infections worldwide, is further divided into 9 different subtypes which dominate in different countries.
The HIV Conspiracy Theory
There are a few different ideas that have been put forward to explain how HIV came about. The two thrown around most, by far, are: “The government did it,” or “It was definitely people having sex with monkeys!”
There are lots of conspiracy theories surrounding HIV; some people do not believe it causes AIDS at all, and others believe that HIV is a man-made virus.
According to a 2005 survey of African Americans living in the US, almost 50% of the respondents believed that HIV was manufactured in a lab. Furthermore, over 25% believed that this was done by the government. A significant number also believed that it was created in order to control the population of black people/homosexuals.
There is absolutely no evidence in support these theories and a lot of evidence to suggest they’re baloney. Some of the earliest documented cases of HIV were in the late 1950s; it’s absurd to think that scientists would have had the knowledge or technology to create viruses back then. We only identified the structure of DNA in 1953. We’ve only just managed to create the first synthetic bacterial genome, let alone create a virus from scratch.
Creating a virus would require knowledge of genetic manipulation. We simply did not have the expertise to be able to achieve something like this at that time.
Tracing The Origin Of HIV
There exists an overwhelming amount of evidence to suggest that HIV arose from cross-species transmission of closely related viruses that are found naturally in various primate hosts in Africa.
By looking at the genomes of these viruses, which are collectively known as simian immunodeficiency viruses (SIV), and comparing them with those of the different types of HIV we can see that the SIVs are the closest relatives of HIV. Furthermore, geographical correlations exist between SIVs in their different hosts and HIV.
HIV-1 and HIV-2 have different origins as they arose from independent transmission events. Closely related SIVs have been found in monkeys called sooty mangabeys in Western Africa, which is the only region that HIV-2 is endemic in. Therefore, scientists conclude that HIV-2 has its origins in SIV infected sooty mangabeys.
HIV-1 is a little more complicated, but each different group (M, N, O and P) arose from a single transmission event. M and N have been traced back to SIV infected chimpanzees (Pan troglodytes troglodytes), but the closest relatives of O and P have been found in gorillas.
When Did HIV Enter The Population?
By looking at the genome sequences of different viruses over time, researchers can calibrate a “molecular clock” based on the rate of sequence change, or mutations. Scientists can then use this to infer the rate of evolution and thus determine approximately when the most recent common ancestor existed.
We Know When, What About How?
There are a few different theories about how these viruses got into the population. The idea that humans copulated with primates and subsequently became infected tickles the fancy of some, but this idea is not taken seriously by experts in the field! (A gorilla? Really?!)
The simplest explanation is that humans came into contact with the blood or other secretions of infected primates which is perfectly plausible since, for example, sooty mangabeys were both kept as pets and slaughtered for bushmeat in West Africa, the same region that HIV-2 is most prevalent. It would be easy for infected bodily fluids to come into contact with broken skin during the butchering process.
Given the fact that medical resources are costly, it is plausible that during immunization programs in Africa, healthcare professionals would have shared needles, providing ample opportunity to spread infection through the population. This, coupled with an increase in international travel alongside sexual promiscuity and intravenous drug use, seems a logical explanation for the emergence of HIV.
Another theory is that humans became infected from contaminated oral polio vaccines. The vaccine in question was called CHAT which required the use of living tissue for production. The idea was that the kidney cells used in the production line came from SIV infected chimps and thus a large number of people were exposed. However, this theory falls down because as we have seen, not all of the HIVs came from chimps. It’s also extremely unlikely that oral vaccines would result in transmission since, unless compromised, the mouth is a pretty good barrier to infection. Furthermore, researchers found stocks of the vaccine used and when it was tested, no traces of SIV were found. This theory has therefore largely been refuted.
In sum, while it is difficult to definitively prove where HIV came from, we can make assertions based on the best available evidence. This evidence points to a simian (monkey or ape) origin, not the government. Everyone loves to hear about a good conspiracy theory, but it really does not add up here.
Justine Alford received her PhD in life sciences from Warwick University in 2014. Her work focused on HIV and immunology. She has no conflicts of interest to declare.
Header image “B0002395 Cut-away model of HIV,” by Wellcome Images, via Flickr, used in accordance with CC BY-NC-ND 2.0.