While the origins of smallpox has remained a mystery for centuries, researchers now believe that it dates back 2,000 years earlier than previously thought.
Until recently, the earliest genetic evidence of smallpox, the variola virus, was from the 1600s. And in 2020, researchers found evidence of it in the dental remains of Viking skeletons, pushing its existence 1,000 years earlier.
Now, Italian scientists have used a mathematical equation to pinpoint the beginnings of smallpox, and coupled with pox scarring seen on ancient Egyptian mummies, they have pushed the emergence of the virus back 3,800 years.
“Variola virus may be much, much older than we thought,” said study first author Dr. Diego Forni, from the Scientific Institute IRCCS Eugenio Medea, in Italy.
“This is important because it confirms the historical hypothesis that smallpox existed in ancient societies. It is also important to consider that there are some aspects in the evolution of viruses that should be accounted for when doing this type of work,” Forni said in a news release from the Microbiology Society.
Smallpox was only eradicated recently, relatively speaking, killing at least 300 million people in the 20th century.
In the new study, the researchers found that different strains of smallpox all descended from a single common ancestor. A small fraction of the genetic components found in Viking-age genomes even persisted until the 18th century.
To estimate the origin of the virus, the researchers then accounted for something called the "time-dependent rate phenomenon."
What this means is that the speed of evolution depends on the length of time over which it is being measured. That means viruses appear to change more quickly over a short timeframe and more slowly over a longer timeframe, something well-documented in DNA viruses, according to the study authors.
By using a mathematical equation to account for the time-dependent rate phenomenon, the research team estimated the first emergence of smallpox may harken back to Egyptian times: Ancient mummies, including the Pharaoh Ramses V, who died in 1157 BC, had suspicious scarring.
The findings were published online Jan. 9 in the journal Microbial Genomics.
The U.S. Centers for Disease Control and Prevention has more on smallpox.
SOURCE: Microbiology Society, news release, Jan. 9, 2023