Potentially dangerous viruses and bacteria can be released when permafrost melts. A 2014 study confirmed that microorganisms preserved in permafrost can remain infectious even after being frozen for tens of thousands of years. A major concern is a potential for melted permafrost to expose burial sites containing disease victims whose corpses may contain well-preserved, potentially dangerous pathogens. Victims of smallpox, the Spanish flu, and other infectious diseases are buried in gravesites in the permafrost.
In 2016, an outbreak of anthrax sickened dozens of people in Siberia--the deadly outbreak is believed to have been caused by melting permafrost exposing a reindeer corpse which had been buried for decades.