The origin of AIDS: from monkeys through chimpanzees to humans

Researchers have discovered a new theory about the history of the epidemic and human infection in Africa; A chimpanzee previously preyed on monkeys - each of which carried a different strain of the virus - and became infected; When the virus passed to humans - it mutated

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The prevailing theory about the origin of the AIDS virus is called "the wounded hunter". According to the theory, a hunter who was injured while hunting chimpanzees became infected with the SIV virus that resided in the chimpanzee's body, and began to spread the disease after the virus mutated.

Now an international group of researchers presents another theory: the SIV virus developed in chimpanzees, after a chimpanzee previously preyed on two monkeys of different types, each of which carried a different strain of the virus. After studying the genetic structure of the AIDS virus, the researchers concluded that the two viruses mutated in the chimpanzees' bodies - and became a third type of SIV. When the virus passed to humans, it underwent another mutation and became the AIDS virus HIV-1 (there is another virus known as HIV-2, which originates from a different species of monkey called the "Mangebi").

The researchers, who publish the results of the study in the journal Science, claim that the discovery will remove doubts about the origin of the AIDS virus. "Many people do not believe that the origin of AIDS is from monkeys," said Dr. Beatrice Hahn, a virologist from the University of Alabama who participated in the study. "They think that the origin of the virus is in failed experiments to find a polio vaccine, in contaminated needles or in strange tribal rituals. Our research reveals the illogicality of their arguments", she explains.

The new theory, proposed by a group of researchers from the UK, France and the USA, can be defined as the "wounded chimpanzee theory". To locate the exact origin of the virus, the genetic structure of SIV viruses, carried by eight different types of monkeys, was analyzed.

The researchers tested different segments of the genes and found similarities between two genetic segments discovered in the virus carried by chimpanzees, and segments discovered in viruses carried by two different types of monkeys - Spot-Nosed Guenons and Red-Capped Mangabey. The researchers believe that these monkeys were eaten by a chimpanzee; She was injured among their people, and thus contracted viruses from them. According to the researchers, although in the past it was believed that chimpanzees were vegetarian animals, now they know that they also hunt monkeys.

Human infection - at the beginning of the 20th century

The viruses penetrated the chimpanzee's bloodstream, then mutated and "melted" into a new virus. The researchers do not know when exactly the transmission of the viruses to chimpanzees occurred, but in their estimation it is a relatively new event: the proportion of chimpanzees infected with the new virus is small compared to the proportion of monkeys carrying the SIV.

According to one of the participants in the study, Prof. Paul Sharp from the University of Nottingham in the UK, the SIV virus is considered common among about 30 different types of African monkeys. The monkeys do not show any symptoms of the disease, and the genetic structure of the different strains of the virus is different. "90-50% of all adult monkeys carry this virus," Sharp told the New York Times.

Human infection probably occurred in the first half of the 20th century. According to the popular theory, between 1910 and 1950 a hunter from the West-Central African region hunted more chimpanzees, and contracted the virus after the chimpanzee's blood mixed with his blood. This theory is supported by the data showing that about a third of the chimpanzees in West-Central African countries - such as Cameroon and Gabon - carry the mutated SIV virus.

Advertisement Unions of genetic structure of viruses (recombination) also occur in humans. For example, subtype B of HIV-1 is common in Western Europe and the United States, while subtype C is common in Africa. There are studies that indicate that the E substrain, which is mostly common in Thailand, is a hybrid of the B and C strains. Despite this, no significant differences were found between the strains in regards to the development of the disease and its symptoms.

According to Sharp, the results of the study will allow researchers to focus on a particular strain of SIV and test the monkeys that have developed immunity to it. Sharp added that due to the genetic similarity between chimpanzees and humans, there is a danger that other viruses carried by chimpanzees will be transferred to humans in the future. "Although it is a faint possibility, theoretically it could materialize tomorrow," he said
Source: Yuval Dror, Haaretz
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