Cat Parasite Linked to Fatal Brain Cancer

Toxoplasma gondii linked to a higher risk of brain cancer
Toxoplasma gondii, viewed under SEM. Source: Getty Images
  • Toxoplasma gondii is a parasite that often leads to the formation of cysts in the brains and muscles of humans
  • A newly published research has now identified a link between glioma, a type of brain cancer, and the parasite
  • Researchers found that the presence of T. gondii antibodies made it 3.35 times more likely in the 70-year-old group to develop glioma.

A study, published in the International Journal of Cancer, has found that people with Toxoplasma gondii infection are more likely to develop a type of brain cancer, called glioma. Although previous studies have suggested a link between the two, this is the first possible evidence of an association between the parasite and risk of glioma.

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

James Hodge, co-lead author

According to the CDC, T. gondii is one of the most common parasites in developed countries. It is estimated that 30-50% of the world’s population have been exposed to the parasite. Infection occurs from undercooked meat, contaminated water, and cat feces, most dangerous of all. While most infections present with mild flu-like symptoms, in immunocompromised individuals it may lead to the formation of cysts in the brain.

Toxoplasma gondii Alters Behavior in Humans and Rodents

In the past, T. gondii infections have been linked to schizophrenia, depression, and even altered behavior. A previously published research showed that people with the infection are more likely to get into a car accident. Moreover, scientists have also observed behavioral changes in mice; rodents with the parasitic infection feared cats less and ended up getting preyed on more.

The new research; however, seems to add to the parasite’s effect on the human brain.

The researchers selected participants from two different cancer studies. They formed two cohort groups that involved glioma cases and controls, to help collect data. One group comprised of mostly 70-year-olds, while other had 40-year-olds. Researchers analyzed their blood samples for antibodies specific to Toxoplasma gondii. Antibodies generally indicate previous infection.

Although rare, glioma is an extremely fatal and aggressive brain tumor. 80% of malignant brain tumors are gliomas. Furthermore, the estimated five-year survival rate for the disease is only 5%.

Higher Risk in 70-year-olds

Overall findings of the study showed that among both groups, infection with T. gondii caused a higher risk of glioma. Moreover, the presence of antibodies to one particular parasitic antigen led to the 70-year-old group being 3.35 times more likely to develop glioma. Whereas, the 40-year-old group had a 1.79 times higher risk.

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

Anna Coghill, co-lead author

While the research provides evidence of a link between glioma and T. gondii, it does not establish how this occurs. Therefore, researchers call for further work in the area to investigate this association.


Hodge JM, Coghill AE, Kim Y, et al. Toxoplasma gondii infection and the risk of adult glioma in two prospective studies [published online ahead of print, 2021 Jan 11]. Int J Cancer. 2021;10.1002/ijc.33443. doi:10.1002/ijc.33443

Flegr, J., Havlícek, J., Kodym, P. et al. Increased risk of traffic accidents in subjects with latent toxoplasmosis: a retrospective case-control study. BMC Infect Dis 2, 11 (2002).


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