Smallpox was one of the most deadly diseases on Earth; the BBC estimates that in the 20th century alone, the disease took around 300 million lives. The disease was eradicated in 1980, but a new report suggests that climate change could bring smallpox back.

The bodies of victims of a smallpox outbreak that occurred in Siberia in the 1890s are in danger of being exposed because the permafrost layer of soil in which they are buried is melting, The Independent reported. The bodies could still carry traces of smallpox, which means the disease may be unleashed after 36 years of eradication. The permafrost of the Yakutia region usually melts between 30 to 60 centimeters a year, but this year it melted more than a meter.

“Naturally, the bodies were buried under the upper layer of permafrost soil, on the bank of the Kolyma River,” Boris Kershengolts, of the Siberian branch of the Academy of Sciences, told The Independent. “Now, a little more than 100 years later, Kolyma's floodwaters have started eroding the banks.”

Smallpox is a contagious, sometimes fatal, infectious disease. The Centers for Disease Control and Prevention says there is no specific treatment for smallpox, and the only prevention is vaccination.

Though a recent excavation of the site did not reveal the virus itself, scientists did find fragments of smallpox DNA. This is not the first time that a change in the climate has brought about a disease outbreak. Earlier this summer an anthrax outbreak in the same area of Russia was traced back to a reindeer corpse from 75 years ago that had thawed. In total, the disease killed around 1,500 reindeer and led to the hospitalization of 13 people, including four children. According to The Independent, this area of Russia has around 200 burial grounds of cattle that have died from the disease.

As the climate warms in the Arctic, there is more organic matter for cold-climate bacteria to eat — further increasing the risks of disease.