They found evidence that people infected with Toxoplasma gondii, or T. gondii, have a higher risk of developing rare but highly fatal gliomas.
The parasite can sometimes form cysts in the brain and the inflammation associated with these cysts might be responsible, the researchers reported in the International Journal of Cancer.
A team of researchers led by epidemiologist James Hodge, of the American Cancer Society's department of population science, and Anna Coghill, of the department of cancer epidemiology at the H. Lee Moffit Cancer Center and Research Institute in Florida, looked at the association between antibodies for T. gondii in blood samples and the risk of glioma in two groups of people.
involved 111 individuals enrolled in the American Cancer Prevention Study-II Nutrition Cohort and 646 people listed in the Norwegian Cancer Registry.
"In both cohorts, we observed a suggestive positive association between seropositivity for T. gondii antibodies and glioma risk," the researchers wrote. The glioma associations were stronger for the people who had higher levels of T. gondii antibodies.
T. gondii is a common parasite that most commonly infects people through contaminated food or water from raw or undercooked meat from infected animals. Twenty percent to 50% of the global population have been exposed to the parasite, according to the study.
Gliomas make up the majority -- 80% -- of malignant brain tumors. Glioblastomas are the most common subtype. Glioblastomas have five-year relative survival rates of only 5%.
"Our findings provide the first prospective evidence of an association between T. gondii infection and risk of glioma, results that should be confirmed in independent studies," the researchers wrote.
"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," Hodge said in a statement.
"The findings do suggest that individuals with higher exposure to the T. gondii parasite are more likely to go on to develop glioma," added Coghill. "However, it should be noted that the absolute risk of being diagnosed with a glioma remains low, and these findings need to be replicated in a larger and more diverse group of individuals."
If the findings of the study are replicated, "reducing exposure to this common food-borne pathogen would offer the first tangible opportunity for prevention of this highly aggressive brain tumor," the researchers said.