More than 2,500 years ago, people carried herpes viruses of the HHV-6 type in their genome. This is shown by analyzes of ancient DNA from human skeletons found in various parts of Europe. Accordingly, the virus, which is now responsible, among other things, for three-day fever in small children, has been circulating in human populations for thousands of years and could be passed on from generation to generation as early as the Bronze Age.
Herpes viruses are best known for causing annoying cold sores. But in addition to the herpes simplex virus responsible for it, the family of human herpes viruses includes numerous other representatives that are responsible for, among other things, chickenpox, shingles, Pfeiffer’s glandular fever and various cancers. They all have one thing in common: once you become infected with them, they usually stay with them for life. The viruses hide in our own cell nuclei in an inactive state and can become active again at times when our immune system is weakened. Some even integrate their DNA into our genome.
Virus genome in ancient skeletons
But since when has humanity had to deal with these viruses? In search of an answer, a team led by Meriam Guellil from the University of Vienna analyzed DNA from almost 4,000 human skeletons from sites across Europe. The researchers focused on the human herpes virus type 6 (HHV-6), which causes three-day fever (Roseola infantum) in small children. HHV-6 is usually transmitted via smear and droplet infections and then preferentially implants itself in cells of the immune and nervous system. If this virus integrates its own DNA into the genome of the germ cells, it can also be passed on from parents to their children.
“While HHV-6 infects nearly 90 percent of the human population at some point in their lives, only about one percent carry the virus inherited from their parents in all the cells of their body,” explains Guellil. “These one percent of cases are the ones we are most likely to be able to identify using ancient DNA.” In fact, the researchers found traces of the virus in the genome of eleven of the human skeletons examined. The oldest sample comes from the skeleton of a ten-year-old girl who lived in Italy around 2,600 to 2,800 years ago. The researchers found additional infected people in sites in England, Belgium, Estonia and Russia. “Based on our data, the evolution of viruses can now be traced back over 2,500 years in Europe,” says Guellil.
Inherited for generations
The analyzes revealed that two different subgroups of the virus, HHV-6A and HHV-6B, existed in the human genome more than 1,000 years ago. To this day, some people carry copies of the viruses in their genome, which have probably been passed on from generation to generation over centuries. “Our results show that all chromosomally integrated HHV-6A clades known today were already represented in historical populations,” report the researchers. Unlike HHV-6B, the team found no evidence that HHV-6A had integrated into the human genome again more recently. From this they conclude that it has lost this ability over time.
While an acute infection with HHV-6 usually only causes temporary symptoms that resolve on their own, the viral genome integrated into the genetic material can increase the risk of illness in the long term. “If a copy of HHV-6B is present in the genome, it may be associated with angina pectoris and heart disease,” reports co-author Charlotte Houldcroft from the University of Cambridge in the United Kingdom. The results help to better understand the coevolution of humans and viruses. “Modern genetic data suggests that HHV-6 may have co-evolved with humans since our migration from Africa,” says Guellil. “These ancient genomes now provide the first concrete evidence of their presence in humanity’s distant past.”
Source: Meriam Guellil (University of Vienna) et al., Science Advances, doi: 10.1126/sciadv.adx5460