But this discovery could help to better understand how the HIV virus, which causes the disease AIDS, attacks cells. This work also demonstrates that a virus can indeed evolve to become more virulent – a scientific hypothesis that has been widely studied in theory, but of which there have been only a few examples until now. The Delta variant of the coronavirus has recently been another.
Declining since 2010
In total, the researchers found 109 people infected with this variant, only four of them outside the Netherlands (in Belgium and Switzerland). The majority were men who have sex with other men, similar in age to people infected with the virus in general.
The variant developed in the late 1980s and 1990s, and was transmitted more rapidly in the 2000s. Likely due to Dutch efforts to control the disease, it has been in decline since 2010 It has been named “variant VB”, for “virulent variant of subtype B” – the most common subtype in Europe.
500 mutations
The HIV virus is constantly changing, so each infected person has a slightly different version of it, which mostly doesn’t matter. But the variant discovered has more than 500 mutations. “Finding a new variant is normal, but finding a new variant with unusual properties is not. Even less so with increased virulence,” said Chris Wymant.
The first person identified with this variant in the study was diagnosed in 1992 (albeit with an unfinished version), and the last in 2014. But other researchers have subsequently identified a few people diagnosed later. Once treated, they present no more risk of complications than the others. But then what does this increased virulence mean?
Disease progression is usually measured by the number of CD4 T cells in the blood. These cells, which are part of the immune system, are the target of the virus. However, people infected with the variant had a lower CD4 count than others at the time of diagnosis, with a decline estimated to be twice as fast. The researchers calculated that, without treatment, the dangerous threshold of 350 T-CD4 cells per microliter of blood would be reached in nine months with this variant, compared to three years for the other patients. The viral load (amount of virus in the blood) of people infected with this variant was also significantly higher.
In addition to its virulence, researchers have also shown that it is highly transmissible. For this, they examined the similarities between the different versions of the virus in infected patients. However, these were very similar, suggesting that the virus had not had time to accumulate many mutations before passing quickly from one person to another.
Importance of screenings
“Our results underscore the importance […] regular access to tests for people at risk of contracting HIV, in order to allow early diagnosis, followed by treatment initiated immediately afterwards”, underlined in a press release epidemiologist Christophe Fraser, co-author of the study. This researcher is behind the Beehive project, bringing together data from patients in eight countries, including the Netherlands. Used for this work, they made this discovery possible.
This project was created in 2014 precisely to analyze to what extent mutations in the virus could have an impact on the disease developed. The differences in the severity of the disease from one person to another were in the past interpreted as solely linked to the more or less good capacity of their immune system to defend itself.
The researchers could not explain which specific mutations of the VB variant caused its high virulence, or by what mechanism. They hope that future studies can do this. “This is a warning, we should never be too presumptuous and assume that a virus will evolve to become more benign”, finally underlined Chris Wymant. A conclusion that will be of interest in the context of current debates around Covid-19.