HIV Is Evolving to Be Weaker Than Your Immune System

​The general evolutionary rule of thumb for pathogens and parasites is simple: Don't kill your host before it can successfully transmit your DNA to another host. That general rule, along with some help from anti-retroviral drugs, is slowly turning HIV from a terrifying death sentence into a virus that one day may be much less harmful.

Evidence of HIV's evolution from killer to manageable disease was discovered by Oxford University researchers in human populations in Botswana, where HIV has been a full-blown epidemic for well over a decade. HIV samples taken from there were markedly less virulent than ones taken in South Africa, which ​has the world's largest number of HIV patients but where the epidemic is newer, according to Philip Goulder, an Oxford University researcher and lead author of a ​paper published today in Proceedings of the National Academy of Sciences.

"Theory predicts, all other things being equal, that infections causing new epidemics will reduce in virulence over time because pathogens require host survival to transmit," Goulder wrote.

None of this is to say that HIV, left untreated, is going to be harmless anytime soon. But it does appear as though the virus is evolving in that direction—and more quickly than would be expected naturally, thanks to antiretroviral therapies.

Samples taken from Botswana were roughly 10 percent less virulent than South African samples, a development that Goulder told me "adds maybe 25 percent more time between getting infected and developing AIDS."

"It doesn't mean that it's no longer able to cause disease at all, but if you look 20-50 years ahead, people might be getting infected with a watered-down form of HIV that the immune system can respond to," he said.

Already, roughly 1 in 300 infected people are able to keep HIV in check, indefinitely, at undetectable levels, without any therapy at all. These people are called "​long-term nonprogressors." In a few years, that number could go up to 5 or 10 percent, Goulder said.

"Over tens of decades, maybe the majority of people will be able to control it without treatment," he added.

Diminishing virulence is a normal feature of most pathogens—it's the reason why we're able to live with most herpes viruses without really getting sick. But, in the case of HIV, it seems like modern medicine has actually sped up its evolution from a very dangerous virus to a potentially manageable one.

Highly virulent strains are generally able to be transmitted more easily, but highly virulent strains also cause immunodeficiency quicker. In sub-Saharan Africa, people who appear sick—which skews towards more virulent strains—are the ones who usually get antiretroviral therapy, when it's available. That medically depresses HIV's viral load in patients, making it less likely for them to pass highly virulent strains on to someone else (and also helping delay AIDS symptoms in the infected patient).

What you're left with are people who have "weaker" forms of HIV, meaning that whatever is being passed on is relatively less dangerous.

"In the vast majority of cases, the people who are getting treatment have the most virulent viruses. If you treat those and prevent transmission from those people, well, then you're limiting transmission from the most virulent versions," Goulder said. "Continuing this strategy is just one of the approaches that can potentially help bring this epidemic under control."