London, Oct 2 (IANS): A team of scientists have identified a species group that infected early humans with genital herpes (HSV2), a sexually transmitted infection, nearly two million years ago.

Parathropus boisei was a heavyset bipedal hominin with a smallish brain that walked on two legs and had dish-like face.

It most likely contracted HSV2 through scavenging meat of chimpanzee, and then passed the pathogen to humans when they hunted for food.

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 enter into our bloodline, the researchers said.

"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," said Charlotte Houldcroft, a virologist from Britain's Cambridge University.

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

"HSV2 is ideally suited to low density populations. The genital herpes virus would have crept across Africa the way it creeps down nerve endings in our sex organs - slowly but surely," she said.

According to the research, published in the journal Virus Evolution, the researchers found that somewhere between three and 1.4 million years ago, genital herpes jumped the species barrier from African apes to human ancestors.

"By modelling the available data, from fossil records to viral genetics, we believe that Parathropus 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," Houldcroft noted.