A parasite carried by billions isn’t dormant at all—it’s running a secret survival operation inside the brain.

A common parasite long thought to lie dormant is actually much more active and complex. Researchers found that Toxoplasma gondii cysts contain multiple parasite subtypes, not just one sleeping form. Some are primed to reactivate and cause disease, which helps explain why infections are so hard to treat. The discovery could reshape efforts to develop drugs that finally eliminate the parasite for good.