But the biggest blow they delivered came from something else entirely — smallpox and other infectious diseases that ravaged indigenous populations. They recovered ancient viral DNA from the mummies of two people who died during the early Spanish colonial period in an Inca community in northern Chile. Smallpox is caused by a pathogen called the variola virus. In the Americas, smallpox and other viral diseases killed, according to some estimates, roughly 90% of the indigenous people. Three years later, the World Health Organization declared smallpox the first — and still only — human infectious disease eradicated worldwide.