New research has identified a curious link between a type of brain cancer and Toxoplasma gondii, the tiny “brain-altering” parasite that can be found in undercooked pork meat, rodents, and cats. While the form of brain cancer remains relatively rare and the risk is incredibly low, the new research highlights another strange way in which this so-called mysterious parasite might affect our brains.
The new study, reported in the International Journal of Cancer, has shown that people who have glioma are more likely to have antibodies to T. gondii, indicating that they had a previous run-in with the single-cell parasite.
T. gondii is a single-celled parasite that’s most often spread to humans through undercooked pork or contact with the poop of an infected cat. The US CDC believes over 40 million people in the US carry the T. gondii parasite. The overwhelming majority of people don't display any notable symptoms as their immune system keeps the infection in check. However, it can cause serious illness for people with a compromised immune system.
It’s perhaps best known for its ability to alter the behavior of rodents. Mice that are infected with T. gondii are often said to lose their fear of cats. Considering they’re less scared of cats, they are more likely to get eaten by one, which suits T. gondii, since the intestines of domestic cats are where the species tend to reproduce.
There’s some evidence to also suggest that this parasitic infection can also make humans indulge in more risky behavior. For example, one study found that infected people have an increased risk of getting into a traffic accident. While some scientists now suspect this link with risky behavior in humans has been overstated, many believe it does have some association with a number of neurological disorders, especially schizophrenia.
The new research saw the team sift through two previous cancer studies involving both people with glioma, a type of highly aggressive brain tumor that starts in glial cells, and those without the condition. In sum, their data included two cohorts, one with 37 glioma cases and 74 controls, and another with 323 cases and 323 controls. The two cohorts were made up of demographically different groups of people: the first were around 70 years old at the time of blood draw, while the others were approximately 40 years old.
Overall, they found that the presence of T. gondii was associated with greater odds of having glioma in both cohorts. Furthermore, the presence of one specific type of antibody to T. gondii made it 3.35 times more likely for those in the 70-year-old cohort to be diagnosed with glioma, and 1.79 times more likely for those 40-year old group to have the condition.
“This does not mean that T. gondii definitely causes glioma in all situations. Some people with glioma have no T. gondii antibodies, and vice versa," added James Hodge, co-lead author from the Department of Population Science at the American Cancer Society.
Scientists think T. gondii alters brain function by forming tiny cysts in the brain. So, it’s not a giant leap to see how the parasite might have some link to glioma, just as previous studies have also hinted. However, the exact nature of this relationship isn’t clear, so the researchers say further work is needed to iron out this link and their findings need to be replicated in larger studies.