HIV was in America 10 years before anyone noticed

Newsbeat

“I’ve got gay cancer. I’m gonna die, and so are you.” Gaëtan Dugas, a flight attendant in the 1980s, would reportedly say those now-infamous words to men after he had unprotected sex with them, according to Randy Shilts, a journalist at the San Francisco Chronicle and author of the 1987 book And the Band Played On. Shilts named Dugas the “Patient Zero” of the human immunodeficiency virus (HIV) epidemic in the US, essentially blaming him for bringing the disease to America. Undoubtedly, Dugas passed on HIV to hundreds or even thousands of men he slept with, according to Shilts, which is why it was possible to trace at least part of the first documented (pdf) outbreak in Los Angeles in 1981 back to him. But since the release of Shilt’s book, scientists have been able to wield new genetic technologies to more clearly identify the path HIV has razed through human populations. Today (Oct. 26), scientists from the University of Arizona and the University of Cambridge published work in Nature that uses the most precise viral genome tracking methods available to show that HIV was present in America as early as 1970 or 1971 in New York, about 10 years before it was found Los Angeles. Additionally, they fully mapped out the genetic code of the specific instance of the virus Dugas carried and definitively proved he was not the first to bring it to the US. HIV is a virus that allows another pathogen to do the dirty work of killing its host. It lurks in the body without causing any symptoms, until all of a sudden it starts replicating its genetic material inside immune cells found in the blood, genital secretions, and breast milk. In doing so, the virus destroys these cells, and the body’s immune system weakened and is eventually rendered defenseless against infections normally fought off relatively easily—the condition called acquired immunodeficiency syndrome, or AIDS. HIV is a virus that allows another pathogen to do the dirty work of killing its host. One of the reasons that we don’t have a vaccine for HIV is because of how often the virus makes mistakes during the replicating process. “The virus goes through a round of replications in infected individuals every two or three days, and has a very sloppy set of enzymes that introduce mutations quite often,” says Michael Worobey, an evolutionary biologist at the University of Arizona and lead author of the recent paper. HIV only has a single strand of genetic code called RNA. DNA has two sets of code twisted together; each side acts like a spell check for the other during the copying process. But without a spell check, the genetic code for HIV often has minor typos—not enough for it to cease being a functioning virus, but enough to make it genetically distinct from previous generations. Although scientists can’t tell which mutations are likely to occur next—and thus can’t design an effective vaccine—they know how frequently they happen, which helps them understand how long the virus has been in a given population. When HIV shows up in a new place, “from that point, on you can kind of look at it like planting a seed.” Worobey says. Each mutation is like a new branch that grows off the original virus; for example, in Kinshasa, Democratic Republic of Congo, where HIV has been for a long time, the virus has enough branches to look like an old oak tree. “From that point, on you can kind of look at it like planting a seed.” Tracking the rate of mutations in the virus enabled scientists to follow the virus back to Cameroon in the early 1900s. The HIV that we see today was originally a mutation of the simian immunodeficiency virus (SIV), which occurs in about 40 different species of monkeys, including chimpanzees. In 2006, scientists published work isolating the specific group of chimps in Cameroon that carried the virus that made the jump to humans. How exactly that happens is not known. “The best hypothesis is the cut hunter hypothesis,” David Quammen, a journalist who’s written extensively about HIV, told Radiolab in 2011. Likely, a hunter was killing an SIV-positive chimp as bushmeat, and at some point cut himself, mixing the animal’s blood with his. That strain of SIV had evolved just enough to be able to survive and thrive in a human environment.