Biologists have found traces of the effects of natural selection on the HIV (Human Immunodeficiency Virus). They found that those viruses that accumulate in the blood in larger quantities, and therefore more infectious, are more successful in reproduction. Scientists have followed this trend over the past 10 years, and it seems to be independent of the HIV strategy. The study is published in the journal Nature Communications .
The classical theory of evolution suggests that natural selection acts on all organisms that are capable of multiplying. Therefore, we can assume that it could act on viruses, allowing one of them to reproduce more successfully than the other. However, traces of such exposure are rather difficult to detect.
For such studies, HIV is a very convenient model, since there are a lot of people infected with it, and they regularly get tested. Joel Wertheim from University of California, along with colleagues, collected data on 41,409 patients who underwent blood tests for diagnosis.
They measured the number of viral particles in the blood before treatment. This is a genetically determined trait in HIV that affects the infectiousness of the virus; the more particles there are, the higher their chances of getting into another person’s body, and therefore can be screened.
To evaluate 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 very similar viruses. The larger the cluster size, the more successful a particular virus.
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 in the clusters. Moreover, 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 during the initial diagnosis has changed over the past decade. They found 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 noticed that the number of viral particles in the blood also depends on the degree 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 effects of natural selection on HIV. More infectious viruses, which accumulate in larger quantities in the blood, are found in larger groups of patients – that is, they spread better in the population. Moreover, over time, HIV evolves toward greater infectivity.
Some scientists believe that this may be a logical consequence of the 90-90-90 strategy (90 percent of infected people get a diagnosis, 90 percent of them get 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, judging by new data, the trend towards an increase in infectivity is stable and does not depend on the strategy of fighting the infection.
Recently, scientists have identified a new subtype of HIV – for the first time in 20 years. The development of a biodegradable implant has also recently appeared , which could save people from the need to constantly take medications to fight the virus. In addition, scientists completely cleared the mice from HIV using the CRISPR / Cas9 system and antiretroviral drugs, and the first patient in the world already received CRISPR / Cas9 edited blood cells.