Toxoplasma gondii is a parasite that infects many animals. In the US, 18–80% of cats and 17–29% of humans are infected. Cats play a unique role in its spread, as the parasite’s sexual reproduction can only occur in cats.
Most infected animals remain healthy. However, infections in immunocompromised individuals or fetuses can be deadly. So, it is important to understand the role of cats in spreading the parasite.
Curiously, the parasite alters the behavior of otherwise healthy rats: Toxoplasma gondii infection affects the innate-fear response in rats and induces a fatal sexual attraction toward the scent of cat to make them more easily captured as prey by cats. This influences how the parasite spreads between rats and cats.