Sunday 11 December 2016

Smallpox Virus recovered from a seventeenth century mummy from Lithuania.

Smallpox (or Variola) is the first disease for which a vaccine was developed, and the only disease to date which has been eradicated by an international campaign of vaccination, with the last case reported in October 1977. Cases of Smallpox have been claimed, based upon historical records, dating back around 3500 years in Egypt, India and China. However diagnosing diseases from historical records is notoriously unreliable, and it is difficult to be confident such records do not relate to a similar infection, such as Measles, Chickenpox, or even some now vanished sickness. Major epidemics of Smallpox began to sweep across Western Asia and Europe from the late sixteenth century onwards, from here spreading to the rest of Eurasia, Africa and the New World and persisting until major vaccinations schemes began in the twentieth century.

In a paper published in the journal Current Biology on 8 December 2016, a team of scientists led by Ana Duggan of the McMaster Ancient DNA Centre at McMaster University, Maria Perdomo of the Department of Virology at the University of Helsinki and Dario Piombino-Mascali of the Department of Anatomy, Histology, and Anthropology at Vilnius University describe the isolation of the Smallpox Virus from a seventeenth century mummy of a child recovered from the crypt of the Dominican Church of the Holy Spirit in Vilnius, Lithuania.

Dominican Church of the Holy Spirit, Vilnius. Left: Lithuania is shaded in yellow, with the red star indicating the city of Vilnius, the location of the Dominican Church of the Holy Spirit where the specimen was found and dated to approximately 1654. Dates in black indicate known smallpox outbreaks in nearby countries during the 17th century. Top right: the Dominican Church of the Holy Spirit in Vilnius, Lithuania. Bottom right: the crypt where the child mummy was located. Duggan et al. (2016).

The mummy was carbon dated to between 1643 and 1665 AD, which matches with a recorded historical outbreak of the disease during the Russian occupation of the city in 1655-1661. Comparison of genome of the Viral strain recovered from the mummy to the genomes of other strains of the Virus collected from around the world between 1944 and 1977 revealed that the strain, while clearly closely related to these was less closely related than all the other strains were to one another. It did appear to be closely related to a strain recovered from a three hundred year old mummy from Siberia in 2012, though this Siberian strain yielded only a partial genome making its relationship to other strains, ancient or modern, difficult to assess.

Mummified remains of a young child of undetermined sex from Lithuania. Duggan et al. (2016).

Duggan et al. found that all the twentieth century strains of the Smallpox Virus shared a last common ancestor around 1654, while the Lithuanian strain shared an ancestor with these between 1588 and 1645. Furthermore they found that the modern strains were divided into two distinct lineages, named P-I and P-II, which were calculated to have shared a common ancestor between 1734 and 1793; the P-I strain was particularly associated with European populations, among which widespread vaccination from the end of the eighteenth century onwards changed the disease from an infection of adults to one of children, and the other most abundant in West African and American populations, suggesting that it may have been spread by slavery and colonialism.

The recent common ancestry of the modern strains of Smallpox, and the placement of a seventeenth century Lithuanian strain outside but close to this lineage strongly suggests that Smallpox is a relatively new infection, that first appeared not long before the major epidemics of the sixteenth and seventeenth centuries, and that the supposed ancient reports of the disease almost certainly refer to a different infection.

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