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Meet the hominin species that gave us genital herpes

fpjl2 — Sun, 01 Oct 2017 23:06:35 +0000

Two herpes simplex viruses infect primates from unknown evolutionary depths. In modern humans these manifest as cold sores (HSV1) and genital herpes (HSV2).

Unlike HSV1, however, the earliest proto-humans did not take HSV2 with them when our ancient lineage split from chimpanzee precursors around 7 million years ago. Humanity dodged the genital herpes bullet – almost.

Somewhere between 3 and 1.4 million years ago, HSV2 jumped the species barrier from African apes back into human ancestors – probably through an intermediate hominin species. Hominin is the zoological ‘tribe’ to which our species belongs.

Now, a team of scientists from Cambridge and Oxford Brookes universities believe they may have identified the culprit: Paranthropus boisei, a heavyset bipedal hominin with a smallish brain and dish-like face.

In a study published today in the journal Virus Evolution, they suggest that P.boisei most likely contracted HSV2 through scavenging ancestral chimp meat where savannah met forest – the infection seeping in via bites or open sores.

Hominins with HSV1 may have been initially protected from HSV2, which also occupied the mouth. That is until HSV2 “adapted to a different mucosal niche” say the scientists. A niche located in the genitals.

Close contact between P.boisei and our ancestor Homo erectus would have been fairly common around sources of water, such as Kenya’s Lake Turkana. This provided the opportunity for HSV2 to boomerang into our bloodline.

̽��ֱ��appearance of Homo erectus around 2 million years ago was accompanied by evidence of hunting and butchery. Once again, consuming “infected material” would have transmitted the virus – only this time it was P.boisei being devoured.

“Herpes infect everything from humans to coral, with each species having its own specific set of viruses,” said senior author Dr Charlotte Houldcroft, a virologist from Cambridge’s Department of Archaeology.

“For these viruses to jump species barriers they need a lucky genetic mutation combined with significant fluid exchange. In the case of early hominins, this means through consumption or intercourse – or possibly both.”

“By modelling the available data, from fossil records to viral genetics, we believe that Paranthropus boisei was the species in the right place at the right time to both contract HSV2 from ancestral chimpanzees, and transmit it to our earliest ancestors, probably Homo erectus.”

When researchers from ̽��ֱ�� of California, San Diego, published findings suggesting HSV2 had jumped between hominin species, Houldcroft became curious.

While discussing genital herpes over dinner at Kings College, Cambridge, with fellow academic Dr Krishna Kumar, an idea formed. Kumar, an engineer who uses Bayesian network modelling to predict city-scale infrastructure requirements, suggested applying his techniques to the question of ancient HSV2.

Houldcroft and her collaborator Dr Simon Underdown, a human evolution researcher from Oxford Brookes, collated data ranging from fossil finds to herpes DNA and ancient African climates. Using Kumar’s model, the team generated HSV2 transmission probabilities for the mosaic of hominin species that roamed Africa during “deep time”.

“Climate fluctuations over millennia caused forests and lakes to expand and contract,” said Underdown. “Layering climate data with fossil locations helped us determine the species most likely to come into contact with ancestral chimpanzees in the forests, as well as other hominins at water sources.”

Some promising leads turned out to be dead ends. Australopithecus afarensis had the highest probability of proximity to ancestral chimps, but geography also ruled it out of transmitting to human ancestors.

Ultimately, the researchers discovered the key player in all the scenarios with higher probabilities to be Paranthropus boisei. A genetic fit virally who was found in the right places to be the herpes intermediary, with Homo erectus – and eventually us – the unfortunate recipients.

“Once HSV2 gains entry to a species it stays, easily transferred from mother to baby, as well as through blood, saliva and sex,” said Houldcroft.

“HSV2 is ideally suited to low density populations. ̽��ֱ��genital herpes virus would have crept across Africa the way it creeps down nerve endings in our sex organs – slowly but surely.”

̽��ֱ��team believe their methodology can be used to unravel the transmission mysteries of other ancient diseases – such as human pubic lice, also introduced via an intermediate hominin from ancestral gorillas over 3 million years ago.

New research uses innovative data modelling to predict which species acted as an intermediary between our ancestors and those of chimpanzees to carry HSV2 – the genital herpes virus – across the species barrier.

Herpes infect everything from humans to coral, with each species having its own specific set of viruses

Charlotte Houldcroft

Left: a cast of a P.boisei skull used for teaching at Cambridge ̽��ֱ��. Right: a figure from the data analysis in the study.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Neanderthals may have been infected by diseases carried out of Africa by humans, say researchers

fpjl2 — Mon, 11 Apr 2016 08:23:09 +0000

A new study suggests that Neanderthals across Europe may well have been infected with diseases carried out of Africa by waves of anatomically modern humans, or Homo sapiens. As both were species of hominin, it would have been easier for pathogens to jump populations, say researchers. This might have contributed to the demise of Neanderthals.

Researchers from the universities of Cambridge and Oxford Brookes have reviewed the latest evidence gleaned from pathogen genomes and DNA from ancient bones, and concluded that some infectious diseases are likely to be many thousands of years older than previously believed.

There is evidence that our ancestors interbred with Neanderthals and exchanged genes associated with disease. There is also evidence that viruses moved into humans from other hominins while still in Africa. So, the researchers argue, it makes sense to assume that humans could, in turn, pass disease to Neanderthals, and that – if we were mating with them – we probably did.

Dr Charlotte Houldcroft, from Cambridge’s Division of Biological Anthropology, says that many of the infections likely to have passed from humans to Neanderthals – such as tapeworm, tuberculosis, stomach ulcers and types of herpes – are chronic diseases that would have weakened the hunter-gathering Neanderthals, making them less fit and able to find food, which could have catalysed extinction of the species.

“Humans migrating out of Africa would have been a significant reservoir of tropical diseases,” says Houldcroft. “For the Neanderthal population of Eurasia, adapted to that geographical infectious disease environment, exposure to new pathogens carried out of Africa may have been catastrophic.”

“However, it is unlikely to have been similar to Columbus bringing disease into America and decimating native populations. It’s more likely that small bands of Neanderthals each had their own infection disasters, weakening the group and tipping the balance against survival,” says Houldcroft.

New techniques developed in the last few years mean researchers can now peer into the distant past of modern disease by unravelling its genetic code, as well as extracting DNA from fossils of some of our earliest ancestors to detect traces of disease.

In a paper published today in the American Journal of Physical Anthropology, Houldcroft, who also studies modern infections at Great Ormond Street Hospital, and Dr Simon Underdown, a researcher in human evolution from Oxford Brookes ̽��ֱ��, write that genetic data shows many infectious diseases have been “co-evolving with humans and our ancestors for tens of thousands to millions of years”.

̽��ֱ��longstanding view of infectious disease is that it exploded with the dawning of agriculture some 8,000 years ago, as increasingly dense and sedentary human populations coexisted with livestock, creating a perfect storm for disease to spread. ̽��ֱ��researchers say the latest evidence suggests disease had a much longer “burn in period” that pre-dates agriculture.

In fact, they say that many diseases traditionally thought to be ‘zoonoses’, transferred from herd animals into humans, such as tuberculosis, were actually transmitted into the livestock by humans in the first place.

“We are beginning to see evidence that environmental bacteria were the likely ancestors of many pathogens that caused disease during the advent of agriculture, and that they initially passed from humans into their animals,” says Houldcroft.

“Hunter-gatherers lived in small foraging groups. Neanderthals lived in groups of between 15-30 members, for example. So disease would have broken out sporadically, but have been unable to spread very far. Once agriculture came along, these diseases had the perfect conditions to explode, but they were already around.”

There is as yet no hard evidence of infectious disease transmission between humans and Neanderthals; however, considering the overlap in time and geography, and not least the evidence of interbreeding, Houldcroft and Underdown say that it must have occurred.

Neanderthals would have adapted to the diseases of their European environment. There is evidence that humans benefited from receiving genetic components through interbreeding that protected them from some of these: types of bacterial sepsis – blood poisoning occurring from infected wounds – and encephalitis caught from ticks that inhabit Siberian forests.

In turn, the humans, unlike Neanderthals, would have been adapted to African diseases, which they would have brought with them during waves of expansion into Europe and Asia.

̽��ֱ��researchers describe Helicobacter pylori, a bacterium that causes stomach ulcers, as a prime candidate for a disease that humans may have passed to Neanderthals. It is estimated to have first infected humans in Africa 88 to 116 thousand years ago, and arrived in Europe after 52,000 years ago. ̽��ֱ��most recent evidence suggests Neanderthals died out around 40,000 years ago.

Another candidate is herpes simplex 2, the virus which causes genital herpes. There is evidence preserved in the genome of this disease that suggests it was transmitted to humans in Africa 1.6 million years ago from another, currently unknown hominin species that in turn acquired it from chimpanzees.

“ ̽��ֱ��‘intermediate’ hominin that bridged the virus between chimps and humans shows that diseases could leap between hominin species. ̽��ֱ��herpesvirus is transmitted sexually and through saliva. As we now know that humans bred with Neanderthals, and we all carry 2-5% of Neanderthal DNA as a result, it makes sense to assume that, along with bodily fluids, humans and Neanderthals transferred diseases,” says Houldcroft.

Recent theories for the cause of Neanderthal extinction range from climate change to an early human alliance with wolves resulting in domination of the food chain. “It is probable that a combination of factors caused the demise of Neanderthals,” says Houldcroft, “and the evidence is building that spread of disease was an important one.”

Inset image: Dr Charlotte Houldcroft

Review of latest genetic evidence suggests infectious diseases are tens of thousands of years older than previously thought, and that they could jump between species of ‘hominin’. Researchers says that humans migrating out of Africa would have been ‘reservoirs of tropical disease’ – disease that may have sped up Neanderthal extinction.

Humans migrating out of Africa would have been a significant reservoir of tropical diseases

Charlotte Houldcroft

Erich Ferdinand

Neanderthal man

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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