Nadia Vasil'eva's cat, Whiskers, was diagnosed with toxoplasmosis last year. After the vet visit, she found herself Googling: could she catch it? Could her brain parasites hurt her?\n\nThe good news: she was already one of roughly 1 in 3 people worldwide carrying the microscopic parasite Toxoplasma gondii — and she had no idea.\n\nToxo, as scientists call it, is one of the most successful parasites on Earth. Once it enters your body — usually through undercooked meat or, yes, contact with cat feces — it can settle into your muscles and brain for life. But here is the reassuring part: most people's immune systems keep it in check so well that they never feel a single symptom.\n\n"Our bodies do a remarkable job of protecting us against a barrage of infections without us even knowing," the article notes.\n\nSo why all the fuss? The worry mostly centers on two groups: pregnant women and people with severely weakened immune systems. For an expectant mother who has never been infected before, toxo can cross the placenta and harm the developing baby — potentially causing blindness or neurological problems. In Australia, this happens in only about 0.17 to 2.3 cases per 10,000 births. That risk is low enough that doctors do not routinely screen pregnant women for it.\n\nFor people with compromised immune systems — from bone marrow transplants or advanced HIV, for example — a dormant toxo infection can reactivate into a serious illness. Doctors who treat these conditions are trained to watch for it, and effective treatments exist.\n\nThe parasite also occasionally causes eye infections. In Australia, retinal toxoplasmosis affects roughly 1 in 149 people. Optometrists and eye doctors know how to spot and treat it.\n\nThe situation is different in countries like France, where about half the population carries toxo, and Brazil, where up to 80% of people have been exposed. Higher infection rates there are linked to dietary habits like eating undercooked meat, more stray cats, and climates that help the parasite survive longer in the environment.\n\nAs for the dramatic headlines about toxo affecting behavior — including links to psychiatric conditions like schizophrenia — researchers caution that these are correlations, not proof of causation. Laboratory studies have shown that infected rodents lose their fear of cat smell, which helps the parasite complete its life cycle by getting eaten by a cat. Whether similar effects happen in humans remains unknown.\n\nBack with Nadia: Whiskers recovered after treatment, and she松了一口气 — felt relieved. The reality is that most people carry toxo without consequence, and simple hygiene precautions, like washing hands after handling raw meat or cleaning the litter box, go a long way. There is no need to surrender your cat.\n\nAs scientists continue studying this ancient parasite, one thing is clear: our bodies are far more resilient than we often give them credit for.