The viruses that cause herpes could protect against bacteria, including (at least in mice) the bubonic plague. The plague, or the Black Death, is caused by a microbe called Yersinia pestis. In the 14th century, this microscopic enemy killed off a third of Europe's population.
The Black Death is believed to have been the result of plague, an infectious fever caused by the bacterium Yersinia pestis. The disease was likely transmitted from rodents to humans by the bite of infected fleas.