Viral DNA isolated from ancient human remains reveals the presence of smallpox in 7th century northern Europe, increasing the definitive antiquity of the disease in humans by nearly 1,000 years, according to a new study. It also reveals a previously unknown, now-extinct clade of the smallpox virus that may have been widespread throughout Viking Age Europe. Smallpox - caused by the variola virus (VARV) - was one of the most virulent and devastating human diseases, likely responsible for the deaths of as many as 500 million people in the 20th century alone, with an unknowable human toll for the several previous centuries. Forty years ago, it also became the first and only human disease to become eradicated from the human population. While smallpox eradication is one of the greatest victories of public health, concerns surrounding the potential reemergence or deliberate release of a smallpox-like virus remain. Unfortunately, a great deal about the origin and evolution of smallpox in humans remains a mystery. Current thinking suggests that a variola-like virus ancestor from Africa was transmitted to humans from rodents several thousand years ago and evolved into the highly virulent modern VARV. However, the earliest genetic evidence for the virus only dates back to the mid-1600s. Aside from ambiguous written records that describe possible infections and suggestive skin lesions found in the ancient Egyptian mummy of Ramses V, concrete examples of smallpox in the ancient past have been elusive. Using a high-throughput shotgun approach, Barbara Mühlemann and colleagues searched for ancient smallpox within the recovered archaeological remains of 1867 humans who lived between roughly 31,000 and 150 years ago and recovered viral sequences from 13 individuals - 11 of which were all from Viking Age (~600-1050 CE) northern Europe. In addition to pushing back the earliest evidence for smallpox infection by nearly 1000 years, Mühlemann et al. found that the newly discovered Viking Age VARV lineages represent a diverse, now-extinct sister clade to modern variola viruses, which may have been a widespread in northern Europe for centuries before evolving into the highly virulent and deadly strain of modern times. Antonio Alcamí discusses the study further in a related Perspective.
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Journal
Science