Toxoplasmodi gondii is a parasitic protozoa who's primary host is cats but also infects other mammals, primarily mice and rats but including humans, as part of its life cycle. Infection by Toxoplasmodi gondii is called Toxoplasmosis and may be acute (flu like symptoms) or latent.
Toxoplasmosis is extremely common. Worldwide, about 30% (US 11%; France 88%!) of people about of people have Toxoplasmosis.
Toxoplasmosis is known to cause behavioral changes in rats:
It has been found that the parasite has the ability to change the behaviour of its host: infected rats and mice are less fearful of cats—in fact, some of the infected rats seek out cat-urine-marked areas. This effect is advantageous to the parasite, which is able proliferate if a cat eats the infected rat and thereby becomes a carrier.
Observational studies suggest that latent Toxoplasmosis may also cause behavioral changes in humans (source paper). The observed differences between infected people and non-infected people include:
- Decreased novelty seeking behavior
- Slower reactions
- Lower rule-consciousness and greater jealousy (in men)
- Greater warmth, conscientiousness and moralistic behavior (in women)