Toxoplasma gondii is a one-celled parasite that infects many mammals, especially cats, but also rats and humans, causing a disease called toxoplasmosis. The parasite has a complex life cycle and needs to be inside a cat’s intestine in order to reproduce sexually. The tiny and apparently simple parasite has an amazing ability to control a rat’s behavior in order to transfer out of the rat’s body into a cat’s intestine.
Researchers have discovered that male rats who are infected by Toxoplasma become interested in cat urine. In fact, the same part of their brain which becomes active when a female rat approaches also activates when the infected rats smell cat urine. The rats sniff the urine and are less fearful about the presence of cats in the environment, making them more likely to be killed and eaten by a cat. This enables Toxoplasma to get into the cat’s intestine.
The parasites control the rat’s brain and manipulates the rat’s behavior for its own benefit. This process has been observed before in insects, such as the so-called “zombie” ants, in which a fungus somehow forces the ant to stop its normal behavior and instead help the fungus to reproduce. Now scientists have discovered that a parasite can control the much more complex brain of a rat.
When an infected cat defecates, parasites are released from its body in its feces. It’s safe to keep cats as pets, but cat owners need to be careful when cleaning cat litter and wear gloves or wash their hands afterwards. Indoor cats are much less likely to get infected by Toxoplasma because they’re not eating wild animals. Humans get infected by the parasite by ingesting undercooked meat or bits of cat feces.
In someone with a healthy immune system there are apparently no ill effects from a Toxoplasma infection, apart from initial flu-like symptoms. The CDC (Centers For Disease Control and Infection) states that more than 60 million people are infected by Toxoplasma in the United States.
Some people do experience more serious effects from a Toxoplasma infection, including people whose immune system is not working properly, such as those with AIDS and organ-transplant patients. Previously inactive parasites may also become active in these people. People undergoing chemotherapy may develop toxoplasmosis. In addition, there’s a risk that if a pregnant woman becomes infected the parasite may enter her fetus, who has an immature immune system. Serious symptoms of toxoplasmosis include eye, brain and organ damage.
Researchers have discovered that more people with schizophrenia have Toxoplasma in their brain than people without schizophrenia do. The parasite infection is thought to increase the amount of dopamine produced in the brain. Dopamine is a chemical messenger and has many important functions. Research to being performed to try to work out the exact relationship between Toxoplasma and schizophrenia.