Some examples of viruses that became more deadly over time include those that developed drug resistant variants, and animal viruses such as bird flu, which were harmless to humans initially but then mutated to become capable of killing people, according to Dr. Amesh Adalja, a senior scholar at Johns Hopkins University’s Center for Health Security.
“Flu viruses have developed resistance to certain antivirals that make them more difficult to treat, and therefore make them more deadly,” Adalja said, also noting the same has happened with HIV and certain Hepatitis C strains.
