This ancient negro primate may be responsible for genital herpes

[Jiggles Boo]

Our ancestors have been catching herpes since before we were
human. The infection is quite common today; the World Health
Organization estimates that two-thirds of adults under 50 are
infected with the herpes virus that causes oral cold sores. One
in six have genital herpes.

Yet humans might have dodged herpes' below-the-belt blow if it
weren't for an ancient encounter between early members of our
genus and a more distant primate relative.

Blame genital herpes on Paranthropus boisei, a heavy-jawed
primate with teeth so large teeth it earned the nickname the
Nutcracker Man. So say a team of virologists and anthropologists
hunting for herpes's ancient origin. Their statistical detective
work, meshing geographic and fossil evidence, was published in
the journal Virus Evolution on Sunday.

Herpes viruses are as varied as they are old. There are more
than 100 different kinds of herpes. Eight regularly infect
humans, causing diseases like chickenpox and mononucleosis. What
we commonly call herpes are two types of incurable herpes
simplex viruses, HSV-1 and HSV-2. Oral cold sores are almost
always caused by HSV-1. HSV-2 is typically sexually transmitted.
(Spikes in HSV-1 genital infections, attributed to a rise in the
popularity of oral sex, have muddied the distinction.)

Our closest living relatives, gorillas and chimpanzees, get
herpes simplex infections, too. “Every other species of primate
only has one kind of herpes simplex virus,” said Charlotte
Houldcroft, a virologist at the University of Cambridge in
England. Houldcroft and her colleagues suggest that a long-ago
meeting of two primates — when Paranthropus boisei met Homo
erectus — explains why our story is different.

Scientists had previously analyzed the herpes genome and created
a viral family tree. Oral herpes, HSV-1, has been around since
humans and chimpanzees split 6 million years ago, as The
Washington Post reported in 2014. The researchers also
discovered that HSV-2 must have jumped from ancestral
chimpanzees into the human lineage later, as recently as 1.4
million years ago.

Houldcroft and her colleagues used a statistical model, called a
Bayesian network, to link primate species through possible lines
of transmission. The authors collected half a dozen possible
culprits from 30 prehistoric species. The ancient patient zero
had to share paleontological time and geographic space with a
human ancestor.

“It was almost like a murder mystery: Who had motive and
opportunity? Who was in the right place at the right time?”
Houldcroft said. In the model's most likely scenario,
Paranthropus boisei infected a human ancestor called Homo
erectus.

“They’re writing the history,” said Joel Wertheim, an
evolutionary biologist who studies infectious disease at
University of California, San Diego's medical school. Wertheim,
part of the team who conducted the 2014 herpes genomic analysis,
was not involved with this new research. He called the recent
study a “detailed, textured history of the geography of these
ancestral species.”

The event must have involved swapping bodily fluids. “You can
speculate in any scurrilous way that you like because we can’t
be sure,” Houldcroft said. But she said she believes violence
was the answer. Perhaps our ancestor killed and ate a
Paranthropus boisei. Perhaps Homo erectus scavenged on
Paranthropus boisei's corpse. Perhaps the Nutcracker Man chomped
on an attacking Homo erectus in defense.

“The idea that it possibly would have jumped over during a
violent encounter, butchering and eating, is actually very
similar to the way modern chimp viruses have jumped into
humans,” Wertheim said. People who butchered chimpanzee
carcasses, he said, were the first exposed to the pandemic
strain of HIV.

Rick Potts, a paleoanthropologist with the Smithsonian’s Human
Origins Program, said that this scenario was possible. The
evidence is good that the species overlapped 2 million and 1.5
million years ago, he said. Archaeologists have found
Paranthropus boisei fossils in the same landscape as tools made
by Homo erectus.

But Potts said wasn't completely convinced that Homo erectus had
to catch HSV-2 from a hominin like Paranthropus. “It strikes me
that if Paranthropus boisei could have obtained a virus from
ancestral chimpanzee, why couldn't Homo erectus have done so?”
he said.

There are other questions this work cannot answer, such as why
HSV-2, if it incubated in Paranthropus boisei before migrating
to the genus Homo, prefers genital tissues. “That's something
virologists are still doing work to answer,” Houldcroft said.

Primate viruses continue to evolve. “Viruses are constantly
going to be jumping from other species into humans, especially
from other apes,” Wertheim said. “Understanding where these
ancient pathogens came from and how they got into humans can
help us understand where our future pandemics will likely arise.”

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