The virus that causes cervical cancer has been evolving in hominins for 500,000 years and split from its ancestors around the same time that humans and Neanderthals diverged, researchers find.
A study provides evidence that the human papilloma virus (HPV) has adapted within our species, and, further, that Neanderthals passed a sub-strain to humans in Asia roughly 80,000 years ago.
"Understanding the evolution of papillomaviruses should provide important biological insights and suggest mechanisms underlying HPV-induced cervical cancer," wrote the authors, led by Zigui Chen of the Chinese University of Hong Kong and Robert Burk of the Albert Einstein College of Medicine in the US.
HPV is part of a family of large group, called papillomaviruses. It is most commonly transmitted through sexual intercourse and has been identified as the main cause of cervical cancer, which is the fourth most common cancer among women.
Worldwide, more than a quarter of a million women die from the disease each year. The researchers used "molecular clock models" to estimate when HPV16 - the most common and deadly form of the human virus - diverged from other strains.
They also isolated papilloma viruses (PV) in nonhuman primates in order to study the diversity of the virus and its evolution. Analysis of tissue from the primate PV hosts "indicated niche adaptation of viruses to host ecosystems as the first stage of the evolution of oncogenic HPVs".
Based on their findings, the researchers suggest HPV followed "an early ancient intrahost viral divergence model ... followed by viral-host coevolution". A similar type of evolution was suggested for polyoma viruses, herpes viruses, and some retroviruses.
"The current data provides a framework to unravel the mysteries of oncogenic HPV genomes as we expand our understanding of viral-host evolution," they go on to conclude.
The researchers also found that the prevalence of a sub-strain of HPV16 in Asia suggests that Neanderthals passed the virus to modern non-African humans through interbreeding as Neanderthals moved eastward, some 80,000 years ago.
"This notion of viral sexual transmission between groups is reflected in the recent genetic admixture... with evidence of 2 to 4 per cent of nuclear DNA in Eurasians that can be traced to Neanderthals", the authors wrote.
The study was published in the journal PLOS Pathogens.
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