The Cat Connection

Toxoplasma can only have sex inside a cat's gut — nowhere else will do. To get there, it has to ride in through a cat's mouth, which means its prey-animal hosts need to end up eaten.

The scale is staggering. A single freshly infected cat can shed up to 100 million infectious egg-like oocysts in about two weeks, seeding soil and water for over a year. Everything else about the parasite is built to deliver its hosts to the one predator that completes its life cycle.