But they can be turned against us. Two new studies in mice have found that viruses can exploit gut bacteria to gain a foothold in our bodies and evade our immune systems. Our microscopic allies can turn into unwitting collaborators for dangerous infections.

The virus that causes polio is one of them. Before infecting the nervous system and causing paralysis, poliovirus first stakes its claim in the gut, and it relies on the local bacteria to do so. Sharon Kuss from the University of Texas Southwestern Medical Center managed to protect mice from the virus by first treating them with antibiotics, which reduced the number of bacteria in their guts by a million times. As a result, twice as