Last year, scientists discovered the mummy of a child who died of smallpox in the 17th century in the crypt of a Lithuanian church. McMaster University researchers discovered one of the oldest and best-known samples of the smallpox virus inside the mummy and sequenced its DNA. This, the scientists believe, will provide insight into the history of epidemics and trace the evolution of the infection.
It's important to note that smallpox is a highly contagious infection. Mortality rates reach 90 percent, and those who survive are left with numerous scars. In the last century alone, the smallpox virus, known as Variola major, which is one of the main causative agents of smallpox, caused the deaths of an estimated 300-500 million people. Medicine is now considered to have eradicated smallpox, as the last documented case was recorded in Somalia in October 1977. Globally, the infection was eradicated thanks to mass vaccination, which cost approximately $300 million between 1967 and 1979 alone.
Scientists have uncovered evidence that smallpox was a true scourge of antiquity after studying Egyptian mummies dating back 3,000-4,000 years. Experts discovered that some of the bodies were covered in scars that closely resembled those found on the skin of smallpox sufferers. However, according to the results of a new study, these conclusions are premature and raise serious doubts.
A team of scientists led by geneticist Henrik Poinar, well known in scientific circles for his work extracting DNA from pathogenic organisms in ancient human remains, succeeded in reconstructing the genome of the Variola major virus from individual fragments. This was achieved by using a hybridization enrichment technique—the use of so-called RNA decoys, small RNA molecules that capture specific DNA strands. In this case, the RNA decoys used were sequences characteristic of the smallpox virus. They were attached to a special microarray. This made it possible to isolate only the genetic material belonging to the virus, and not that of the deceased child from whose mummy the DNA was extracted.
The fragments obtained were sufficient for a complete reconstruction of the ancient virus strain's genome. Furthermore, they were also sufficient for comparison with the genomes of strains that emerged much later, in the last century. Based on this study, the scientists concluded that all the studied strains share a common ancestor that emerged between approximately 1588 and 1645. Its emergence coincided with the discovery of the New World, the exploration and colonization of new territories.
According to Poinar, scientists have a timeline of viral evolution at their disposal, which allows them to determine whether the recorded historical references to smallpox, dating back to the time of Ramses V and before 1500, were real. The scientist notes that these could indeed have been cases of smallpox, but they are easily confused with chickenpox or measles.
Researchers have also identified different periods of virus evolution. One of the most striking examples of the development of the Variola major virus is the smallpox vaccine developed by the English physician Edward Jenner. In 1796, he successfully vaccinated an eight-year-old boy with cowpox. The child suffered a mild form of the disease, making him immune to the smallpox virus. This incident marked the beginning of the widespread use of vaccination as an effective method of combating the infection. On the other hand, it led to the division of the virus into several strains: the deadly Variola major and Variola minor, which primarily affected children in West Africa.
Biologists remain hopeful that they will eventually be able to find other smallpox virus samples that infected people across Europe and compare their DNA with the genome of the virus discovered in the Lithuanian crypt. This will allow them not only to study the virus's evolution in more detail but also to determine its origins. Researchers already know that smallpox began around 1650, but they still have some questions. Specifically, they don't know how the virus first began infecting humans, nor which animal was its original host.
Although smallpox has been almost completely eradicated, some samples are still stored in laboratories at the Russian Vector Research Center and at the Centers for Disease Control and Prevention in the United States. These laboratories are believed to be the only place where the smallpox virus still exists, but the World Health Organization is considering destroying the entire sample collection.
However, the problem is that the possibility of a resurgence of the infection remains. This is why the heads of research centers are confident that it is premature to completely eradicate the smallpox virus. For example, several years ago, a box containing vials of smallpox virus was accidentally discovered at a public health institute in Maryland. Since there is no guarantee that this is an isolated case, continued research on the virus is essential, including on samples that can help track its development.
