When people say that every cloud has a silver lining, they probably aren’t thinking about herpes at the time. Herpes may be unpleasant, but the viruses that cause it and related diseases could have a bright side. In mice at least, they provide resistance against bacteria, including the bubonic plague.

Herpes is one of a number of itchy, blistering diseases, caused by the group of viruses aptly-named herpesviruses. Eight members infect humans and cause a range of illnesses including glandular fever, chickenpox, shingles and, of course, herpes itself.

Almost everyone gets infected by one of these eight during their childhood. But herpesviruses are for life, not just for Christmas. After your body fights off the initial infection, the virus retreats into