Parasite Found in Undercooked Meat and Cat Poop May Be Linked to Rare Brain Cancer

The U.S. sees about 24,000 brain cancer cases annually, compared to 30 million cases of Toxoplasma gondii, so an individual’s cancer risk is low

An image of toxoplasma gondii under a microscope
Toxoplasma gondii grows in tissue cysts which can stick around in the body after illness has passed Image by the CDC, 1986

Research published this week in the International Journal of Cancer shows that people with glioma, a type of brain cancer, are more likely to have been infected by the “cat litter parasite” Toxoplasma gondii than people without the cancer.

The results are a promising first step on a path to reduce people’s risk of developing glioma, Naomi Thomas reports for CNN. The new study looked at incidents of brain cancer and T. gondii in just over 750 people involved in two cancer prevention studies. The study’s authors and outside experts agree that in order to prove a connection, further research in larger groups of people will be necessary, Ashley P. Taylor reports for Live Science.

If additional studies confirm their findings, the researchers conclude in their paper that “reducing exposure to this common food-borne pathogen would offer the first tangible opportunity for prevention of this highly aggressive brain tumor.”

About 11 percent of people in the United States have been infected with T. gondii before, according to the Centers for Disease Control and Prevention. Most catch it from either undercooked meat, usually pork, or from feces of domestic cats. T. gondii parasites spend about half of their lives living inside of cats’ digestive systems, so an infected cat’s poop may contain the parasite. In some cases, a person can become exposed to the parasite when cleaning a cat’s litterbox.

For healthy people, a T. gondii infection won’t cause any illness, and rarely, it causes mild flu-like symptoms for a few weeks. The parasite can have severe effects for pregnant women and the fetus and for people with compromised immune systems. Even when illness subsides, the parasite can stick around in the body in an inactivated form. Recent studies have suggested a connection between T. gondii infections and increased risks for schizophrenia and behavioral changes, Ed Cara reports for Gizmodo.

The new study joins a few others that have suggested a connection between brain cancer and T. gondii, but it is the first to show clearly that the parasitic infection happened before the cancer developed. The U.S. sees about 24,000 new cases of brain cancer per year, compared to over 30 million cases of T. gondii, so an individual’s risk of developing brain cancer after an infection is low.

The researchers used blood samples from about 750 people to look for antibodies—a sign that they’d been infected in the past—to many diseases, including T. gondii. Then they compared the antibodies found in the people who developed cancer to a group of people who didn’t have cancer. T. gondii emerged as an infection more common in people who had cancer.

University of Salford parasitologist Geoff Hide, who wasn’t involved in the study and previously published a study linking the parasite to lung cancer, tells Live Science that "in principle, reducing T. gondii exposure is likely to prevent some gliomas — probably because the immune system is less stressed."

"This does not mean that T. gondii definitely causes glioma [brain cancer] in all situations,” says epidemiologist James Hodge in a statement. “Some people with glioma have no T. gondii antibodies, and vice versa.”