Toxoplasmosis.
That’s a big scary word. What it means is an infection with a parasite known as Toxoplasma gondii or T. gondii. And many millions of us are infected. Especially if you are owned by a cat. For the most part such infections are harmless and cause no symptoms or known problems but at times it can cause a flu-like syndrome and rarely severe illness. Here is an article from the CDC on this interesting little critter.
What’s interesting about a T. Gandii infection, or exposure, is that it causes an immune response in humans that is similar to that found in cancer victims. It’s possible that exploiting that immunological reaction could be a useful approach to cancer treatment. Much research lies ahead but it is interesting.