Toxoplasma gondii, a parasitic protozoan, infects more than 50 percent of people on Earth and millions of cats and other animals, yet the secrets to its success have largely remained a mystery—until now. A new study published in the journal Structure concludes that the parasite can hack into and rewire its host’s immune system to suit its own purposes.

You may not recognize this parasite by name, but you’ve probably heard it mentioned. T. gondii infection, better known as toxoplasmosis, has the power to produce strange changes in its hosts. The parasite can only reproduce within a cat’s body, and scientists believe that it can manipulate other animals to make that happen. Mice with toxoplasmosis lose their healthy fear of cats and will stroll right up to their predators, essentially delivering their parasitic passengers directly into the mouth of the beast.

Some scientists believe that toxoplasmosis can also influence human behavior, and studies have linked infection to symptoms of schizophrenia, bipolar disorder, and intermittent explosive disorder. Other researchers say these findings are overhyped, overblown, and impossible to reproduce.

Whether or not T. gondii can change our minds, it’s definitely changing our bodies. Toxoplasmosis can be dangerous for pregnant women and people with compromised immune systems, but most people never even know they’re sick—which is not how our bodies are supposed to work. Our immune systems are supposed to protect us from parasites like T. gondii, or, if they can’t, at least alert us by getting riled up and inflamed.

But somehow, this intruder found a way to override our personal security systems. The first clue to its strategy came last year, when scientists at the Institute for Advanced Biosciences discovered that T. gondii makes a protein called GRA24 that in turn convinces the body to make an inflammatory protein called p38α.

This raised a new question, one which became the focus of the new study: Why would a parasite ever want to trigger inflammation?

The researchers cultured human cells in the laboratory, then gave them toxoplasmosis and monitored the molecular-level interactions between the two proteins. They discovered that GRA24 can essentially hot-wire the security system and bypass multiple steps of the immune response process. By making its own p38α, T. gondii can control the flow and extent of inflammation. It doesn’t shut down the immune system; doing so could make its host sick and jeopardize the parasite’s new, cushy existence. Instead, it muffles the system just enough to keep itself safe and undetectable.

Watch your back, T. gondii. We're on to you.