Tracing the long, convoluted history of the AIDS epidemic

The common narrative holds that the spread of HIV and AIDS among humans can be traced back to one flight attendant in the 1980s. But while that individual certainly did spread the virus, he was far from the first to do it. In fact, humans had been infected with HIV as far back as at least the early 1900s, writes renowned science journalist David Quammen, who traced the genetic origins of the AIDS epidemic by reviewing scientific literature, consulting researchers and traveling to the geographic source of the deadly disease.

The story Quammen puts forward in his newly published work, “The Chimp and the River: How AIDS Emerged From an African Forest,” is an edited and reshaped version of a chapter from “Spillover,” his much larger 2012 book about zoonotic diseases. “The AIDS pandemic results from a single spillover of what was a chimpanzee virus, from one chimpanzee to one human, in the southeastern corner of Cameroon back around 1908, give or take a margin of error,” Quammen told The Post. But unless you’ve been paying close attention to developments in scientific literature, Quammen said, “that’s shockingly different than what we knew.”

For “Spillover,” Quammen spent 12 years tracing the animal origins of a number of diseases, with travels taking him to the far corners of the globe. The title won multiple science and biology book awards and earned raves: New York Times critic Dwight Garner called Quammen “not just among our best science writers but among our best writers, period.” (“That he hasn’t won a nonfiction National Book Award or Pulitzer Prize is an embarrassment,” Garner added.)

Last year, drawing on “Spillover,” Quammen released a similar standalone book on the history of the Ebola virus. Whereas Ebola’s worldwide death toll is in the thousands since the first outbreak in 1976, more than 39 million people have died from HIV/AIDS over the years, according to the World Health Organization, which says an additional 35 million have been infected.

“Knowing the origins of a disease like [AIDS] is crucially important for preventing instances of the same sort of thing,” Quammen said.

With Ebola, for instance, learning about the animal origins of the virus could help stop the next outbreak before it happens. “That’s true of AIDS also, but it’s different with AIDS because it’s already killed [millions of] people and it’s in the human population for good. People are not worried about the next spillover because this one is already so horrible.”

Quammen looked to scientists who have done much work to help answer the where, when and how of HIV’s animals-to-humans transition. For the question of “when,” he sought out the University of Arizona’s Michael Worobey, who published a paper in the journal Nature in 2008 that detailed the genetic analysis of biological samples from taken from two HIV-infected humans decades before.

One of these samples dates back to 1959, and the other to 1960. Worobey and his team “looked at the genetic sequences of these two specimens, and he combined that with a molecular clock with how fast HIV generally changes, mutates and evolves,” Quammen said. “He saw these were two branches of a tree, and the point where they diverged from a larger limb, was essentially 51 years earlier.”

That means that HIV jumped from a chimpanzee to a human, at the latest, around 1908, give or take some years. (The calculation is an estimated time frame.) The jump could have happened prior to that, Quammen said, but the research shows it couldn’t have first happened later.

Quammen then looked at the work of Beatrice Hahn, then of the University of Alabama at Birmingham, to learn more about where this spillover may have happened. Researchers knew that HIV came from a precursor chimpanzee virus, called SIV. Using a new method to detect traces of viruses by examining fecal matter and urine, Hahn and her team decided to find out which chimpanzees had the SIV from which HIV came; they screened samples from all over Africa, looking for what is “essentially a chimpanzee version of HIV,” Quammen said.

Of particular interest, he noted, is HIV-1 group M, which is the strain responsible for the global AIDS pandemic. In 2006, Hahn and her team discovered that the virus’s genetic diversity was reflected in chimp SIV from one particular part of central Africa.

So how did that first chimp infect a human? “That is unknowable. People want to immediately say a human had sex with a chimpanzee,” Quammen said. But that scenario is not the most plausible, and therefore not the likely way it happened, he noted.

The more sound theory, Quammen said, is the “Cut Hunter” hypothesis: A hunter who butchered an SIV-infected chimpanzee somehow made contact with its blood, perhaps through an open wound.

Quammen eventually visited the very place likely to be the location of the spillover: The infected humans likely carried the virus through a series of rivers to the current city of Kinshasa in the Democratic Republic of Congo, he said.

Learning about the origins of a virus is more than just an interesting, historical exercise; it can provide insight as researchers work on therapies and potential cures, Quammen said.

“It’s bound to be helpful to understand how this virus works, how did it evolve and how it continues to evolve,” he said. “People have to understand that one of the things that makes AIDS a really difficult disease is the HIV virus is constantly evolving, constantly changing. … So understanding its evolutionary history is part of understanding why it’s such a problematic virus.”

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s