Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii, one of the world’s most common parasites. Infection usually occurs by eating undercooked contaminated meat, exposure from infected cat feces, or mother-to-child transmission during pregnancy. In the United States, it is estimated that 11% of the population six years and older have been infected with Toxoplasma. The parasite has been linked with Alzheimer’s disease, Parkinson’s disease, epilepsy, and cancer. Now a new study suggests a link between the parasite infection and the risk of glioma, a type of brain tumor.

The findings were published in the International Journal of Cancer in a paper titled “Toxoplasma gondii infection and the risk of adult glioma in two prospective studies.”

T. gondii is a common parasite that shows affinity to neural tissue and may lead to the formation of cysts in the brain. Previous epidemiologic studies have suggested an association between glioma and increased prevalence of T. gondii infection, but prospective studies are lacking. Therefore, we examined the association between prediagnostic T. gondii antibodies and risk of glioma in two prospective cohorts using a nested case‐control study design,” noted the researchers.

The study was led by James Hodge, an epidemiologist at the American Cancer Society and Anna Coghill, PhD, an assistant member at the Moffitt Cancer Center & Research Institute. The researchers observed the association between T. gondii antibodies measured several years before the cancer was diagnosed and the risk of developing a glioma. Participants were from the American Cancer Society’s Cancer Prevention Study-II (CPS-II) Nutrition Cohort and the Norwegian Cancer Registry’s Janus Serum Bank (Janus).

Although glioma is a relatively rare disease, it is a highly fatal cancer. Gliomas are the most common type of primary brain tumor. They can occur at any age and part of the brain or spinal cord where the glial cells—the support cells of the nervous system—are located. The majority (80%) of malignant brain tumors are gliomas, for which the estimated five-year relative survival rate is a stark 5%.

The researchers noted an association between T. gondii antibodies and glioma was similar in two demographically different groups of people: the CPS-II cases were approximately 70 years old at the time, while those in the Janus cohort were approximately 40 years old.

“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,” explained Hodge.

“Blood samples collected prior to diagnosis were analyzed for antibodies to two T. gondii surface antigens (p22 and sag‐1), with individuals considered seropositive if antibodies to either antigen were detected,” the researchers wrote. “Conditional logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI) for each cohort. In both cohorts, a suggestive increase in glioma risk was observed among those infected with T. gondii (OR: 2.70; 95% CI: 0.96‐7.62 for CPSII‐NC; OR: 1.32, 95% CI: 0.85‐2.07 for Janus), particularly among participants with high antibody titers specific to the sag‐1 antigen (CPSII‐NC OR: 3.35, 95% CI: 0.99‐11.38; Janus OR: 1.79, 95% CI: 1.02‐3.14).

“The findings do suggest that individuals with higher exposure to the T. gondii parasite are more likely to go on to develop glioma,” said 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.”

Their study is the first prospective evidence of an association between T. gondii infection and risk of glioma. Further studies with larger case numbers are needed to confirm a potential etiologic role for T. gondii in glioma.

The authors noted, that “if future studies do replicate these findings, ongoing efforts to reduce exposure to this common pathogen would offer the first tangible opportunity for prevention of this highly aggressive brain tumor.”