As the world warms, permafrost soils that have been frozen for thousands years are melting, releasing ancient viruses and bacteria that have lain dormant, reports the BBC.

The first case: Last August, in a remote part of the Siberian tundra in the Arctic Circle, a 12-year-old boy died and at least 20 people were hospitalized after being infected by anthrax.

• The theory: Over 75 years ago, a reindeer infected with anthrax died and its frozen corpse became trapped under a layer of frozen soil, or permafrost. The remains stayed there until a heatwave in 2016 melted the permafrost. The exposed carcass then released its anthrax into nearby water and soil, and made its way into the food supply.

Why this matters: Scientists worry this will not be an isolated case. As the Earth continues to warm, more permafrost will melt, and expose years of dormant diseases.