The evolution of HIV
HIV caught on evolution towards greater contagion
Polina Loseva, N+1
American biologists have found traces of the action of natural selection on the human immunodeficiency virus. They found out that those viruses that accumulate in the blood in greater quantities are more successful in reproduction, which means they are more contagious. Scientists have traced this trend over the past 10 years, and from the strategy of combating Apparently, she does not depend on HIV. The study was published in the journal Nature Communications (Wertheim et al., Natural selection favoring more transmissible HIV detected in the United States molecular transmission network).
The classical theory of evolution assumes that natural selection acts on all organisms that are able to reproduce. Therefore, it can be assumed that it could also act on viruses, allowing one of them to reproduce more successfully than others. However, it is quite difficult to detect traces of such an impact.
For such studies, HIV is a very convenient model, since there are quite a lot of people infected with it, and they are regularly tested. Joel Wertheim from the University of California, together with colleagues, collected data on 41,409 patients who took blood tests for diagnosis.
The number of viral particles in their blood was measured before the start of treatment. This is a genetically determined trait in HIV that affects the contagiousness of the virus — the more particles, the higher their chances of getting into another person's body — and therefore can be selected.
To assess the success of the spread of viruses, the researchers compared their reverse transcriptase gene sequence and isolated genetic clusters — groups of patients who are infected with the same or extremely similar viruses. The larger the cluster size, the more successful a particular virus is.
Scientists have found that in those patients who are part of the genetic clusters, the concentration of the virus in the blood is significantly higher (p<0.001) than in patients who are not part of the clusters. At the same time, in people who were diagnosed at an earlier stage of the disease, this dependence is stronger than in those who received it later.
Then the authors of the work checked how the number of viral particles in the blood at the initial diagnosis changed over the past decade. They found out that the viral load at all stages increased (p<0.001) from 2007 to 2016. For example, in the early stages of the disease in 2007, an average of 13020 particles per milliliter of blood were found in patients, and in 2016 — already 22100.
In addition, scientists have noticed that the number of viral particles in the blood also depends on the extent to which the patient (or rather, the virus with which he is infected) is included in the genetic cluster. That is, each additional genetic link increased the viral load (p<0.001).
Thus, the researchers found traces of the action of natural selection on HIV. More contagious viruses, which accumulate in larger amounts in the blood, occur in larger groups of patients — that is, they spread better in the population. At the same time, over time, HIV evolves towards greater contagiousness.
Some scientists believe that this may be a natural consequence of the "90-90-90" strategy (90 percent of infected people receive a diagnosis, 90 percent of them receive therapy, 90 percent of them get rid of the virus in the blood) and that it may favor the development of more infectious strains. However, according to the new data, the trend towards increased contagion is stable and does not depend on the infection control strategy.
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