The herpes simplex virus, or HSV1, is one of the most pervasive viruses among humans. A new study suggests the virus might have a more recent and tumultuous evolutionary path.
According to the World Health Organization, as of 2016, over 65% of the population of people aged 50 and below carry a variant of HSV1. Like many diseases the exact origin of the virus, or when humans first contracted it, remains unknown. So here are the basics: HSV1 is a double-stranded DNA virus that is easily transmissible. When triggered by stress, either psychologically or physically, it can result in lesions and sores.
According to a recent Science Advances publication, it affects two-thirds of the world's population.
Some cases can lead to more extreme side effects, and more extreme strains (such as HSV2, the genital herpes complex) can present differently. While many people don't outwardly show many symptoms after infection, people with immunocompromising or pre-existing conditions can present more extreme symptoms. Many genetic variants also factor in susceptibility and can be fatal in rare cases.
Recent genetic research by an international team led by the University of Cambridge has begun to establish a timeline for the evolution of the virus combined with newer cultural practices that were spreading during the neolithic period, AKA the onset of agriculture, and the Bronze Age.
The primary theory behind the early spread of herpes simplex viruses was that, since it originated in primates living in Africa, it must have then spread from there with early human migration out of Africa. However, a 2020 study challenged that assumption and showed that most current worldwide strains of HSV-2 left the African continent in the relatively recent past, coinciding with the 18th-century transatlantic slave trade. As for HSV-1, they estimate that there was a change in the virus about 5,000 years ago. This is where the archaeologists come in.
Archaeologists and genetic researchers working with aDNA (ancient DNA) have uncovered a possible sequence of information and events regarding the spread of the HSV-1 viral strain of facial herpes. The team can now begin to piece together the puzzle by sequencing ancient genomes.
In Europe, some samples were taken from three adult males and one adult female from various medieval cemeteries (3rd - 17th centuries CE). The oldest sample is an adult male from the Iron Age in Russia’s Ural Mountains (about 1,500 years old). Two others from the UK were an adult female (6-7th century CE) and a young adult male (late 14th century). And, finally, a young adult male from late-17th century Holland.
By targeting aDNA extracted from deep within the root of the teeth, the team could identify HSV-1 in these four individuals and use the viral genome to estimate the virus's origin. Using a comparison of ancient and modern viral DNA extractions, a rough phylogeographic analysis (the study of genotypes and their geographic relationships) was initiated to test the out-of-Africa theory and date the HSV-1 virus. The study concludes that the virus's more recent spread ca. 5,000 years ago was not due to any change in the virus itself but rather could be attributed to changes in human behavior and interactions. The Bronze Age saw population density in permanent communities increase. That, plus human migratory patterns and the influx of new cultural and interpersonal practices (romantic kissing and touching).
Based on the geographic circulation of strains previously documented and known, it suggests the distribution of the virus is more likely a more recent coevolutionary events. Scientists think large-scale migratory shifts, changes in cultural practices, and high population turnover may have provided paths for certain strains over others. However, new information will always come to light as we continue to test more ancient samples.