Could bacteria or viruses lurking in ancient Egyptian mummies unleash a plague today?

The ancient Egyptians were no strangers to illness, with research showing that they were affected by a host of infectious diseases, including smallpox, tuberculosis and leprosy.

For instance, Ramesses V, the fourth pharaoh of Egypt's 20th dynasty, contracted smallpox, which is evidenced by telltale smallpox scars pockmarking his mummified body. 

Even though the World Health Organization (WHO) officially declared smallpox eradicated worldwide in 1980, is it possible that, thousands of years later, newly unearthed mummies could unleash smallpox or any other illnesses from their bodies? 

Piers Mitchell, director of the University of Cambridge's Ancient Parasites Laboratory and a senior research associate in its Department of Archaeology, said it's extremely unlikely. 

"Most species of parasites are dead within a year or two" without a living host to latch onto, Mitchell told Live Science. "If you wait more than 10 years, everything is dead." 

Related: 7 famous mummies and secrets they've revealed about the ancient world

For example, poxviruses like smallpox can only reproduce within the cells of a living host, according to the National Library of Medicine’s National Center for Biotechnology Information at the National Institutes of Health (NIH). The bacteria that causes tuberculosis and leprosy also require living hosts to survive, according to the NIH.