“Every cloud has a silver lining,” that’s what people say sometimes. But they’re not thinking about HSV at the moment. HSV or the herpes simplex virus can be unpleasant, but the viruses that activate it and other related diseases can have a benefit. At least in mice, they provide bacterial resistance against diseases such as the bubonic plague.

Herpes is just one of several blistering and itchy infections caused by the group of viruses aptly called the herpes virus. Eight members of the group of viruses infect humans and cause various diseases, including chickenpox, shingles, glandular fever, and indeed herpes itself.

Almost everyone gets one of these viruses during their childhood. But the group of viruses will remain in the body permanently; not just for the holidays. After your immune system fights off the primary infection, the virus enters an inactive phase called “latency.” It remains hidden, without showing apparent symptoms. But it is likely that it will be reactivated at any time.

In this way, herpes viruses are like parasites for life, ensuring their own survival and causing damage to the health of their host. In extreme cases, latent viruses can cause chronic inflammation, which in turn can lead to autoimmune diseases or some forms of cancer.

But there is also a good side to herpes. Erik Barton and his colleagues at the Washington University School of Medicine found that, once infected, the mice entered the latent phase and became surprisingly resistant to certain types of bacteria. Unlike their susceptible and uninfected companions, they are even capable of fighting off the fatal plague insect, Yersinia pestis.

At least in mice, dormant herpesviruses become paying tenants rather than profiteering squatters; resistance to bacteria is your rent. The latent phase is vital to the effect of resistance, and Barton discovered that a mutant herpes virus infects but provides nothing in return to its host.

Viruses work by alerting the immune system. The effect is similar to that of a terrorist alert, causing an intensified level of security where the body is ready to protect itself from any threat. Viruses activate the release of cytokines at high levels. Cytokines are chemicals in the immune system. These molecules, including IFN-g (interferon-gamma) and TNF-a (tumor necrosis factor alpha), help coordinate defense against infection.

These chemicals activate macrophages, a white blood cell. These cellular killers consume invading bacteria and digest it. They are activated in large numbers in mice infected with the herpes virus in the latent stage. This sequence is the way the immune system protects us against various bacterial invaders. However, in Barton’s study, the protection was initiated by viruses and persisted longer than usual. Good for the mice.

What do we gain from these viruses? Will it have the same effect on us as mice? Barton thinks so. In his research, two different strains, gHV68 (murine herpesvirus gamma 68) and MCMV (murine cytomegalovirus), had a similar effect. He thinks that bacterial resistance is a universal feature of all herpes viruses.