A new study revealed that one of the most viral diseases ever to affect humans has evolved far more recently than previously thought.

The study, published in the journal Current Biology, showed that all the available strains of the virus, which causes small pox, have an ancestor no older than 1580. This could potentially debunk previous claim about the disease terrorizing humans thousands of years ago.

"Scientists don't yet fully comprehend where smallpox came from and when it jumped into humans," said senior author Hendrik Poinar, an evolutionary geneticist and director of the McMaster Ancient DNA Centre, in a press release. "This research raises some interesting possibilities about our perception and age of the disease."

For the study, the researchers captured, sequenced and reconstructed ancient and heavily fragmented DNA of smallpox virus, variola. The variola virus, or VARV, was collected from the partial mummified remains of a Lithuanian child believed to have died between 1643 and 1665.There are no indication of live virus from the reconstructed virus, making the smallpox from the mummies not infectious.

By comparing and contrasting the strain taken from the Lithuanian child to those from a modern databank of samples dating from 1940 up to its eradication in 1977, the researchers were able to discover that the evolution of VARV occurred far more recently than previously thought, with all the available strains of the virus having an ancestor no older than 1580.

Additionally, the researchers found that the virus have evolved into two circulating strains after the development of its vaccine by English physician Edward Jenner in 1796. One of the forms of VARV is known as V. major, while the other one is known as V. minor. V. major was a highly virulent and deadly. On the other hand, V. minor was much more benign. During the rise of global vaccination efforts against smallpox, the two forms experienced a "major population bottleneck."

With their findings, the researchers were still not sure what animal served as the true reservoir of the smallpox virus before it made a jump into humans. More research is necessary to determine how the virus diversified in the face of vaccination efforts. Furthermore, researchers need to have a better understanding of the virus' origins in order to prepare for its potential reemergence.