A parasite found in cat poop has been linked to a higher risk of brain cancer in humans

• A parasite which reproduces in cats and also spreads to humans through undercooked meat has been linked to an increased risk of glioma, a kind of brain cancer in humans
• However, taking care around cat litter and ensuring you cook your meat will reduce your exposure to this parasite
• The study authors also noted that their findings need to be replicated in a larger group of individuals

The researchers reached their conclusion after discovering the presence of T. gondii antibodies in a group of people's blood (compared to a similar group that was cancer-free) and the development of glioma several years later. The presence of antibodies in their blood means that they had previous exposure to a parasite or pathogen.

Although glioma is the most common type of brain cancer, study co-author James Hodge, an epidemiologist at the American Cancer Society in Atlanta, did, however, caution in a statement by the organisation that the current findings “... do not mean that T. gondii definitely causes glioma in all situations [and that] some people with glioma have no T. gondii antibodies, and vice versa.”

T. gondii and its association with cats

T. gondii is found worldwide and is capable of infecting humans and virtually all warm-blooded animals, although felids such as domestic cats are the only known definitive hosts, in that it can reproduce sexually in the gut of a cat and come out in the faeces, explained Robert Sapolsky, professor of neurology at Stanford University in an article for Nexus. 

Sapolsky was not involved in the study but has spent years researching the parasite, trying to figure out how it has the ability to change the behaviour of its host in a very unique way and how it winds up in various regions of the human brain.

The study results

According to the published paper, an association between T. gondii antibodies and glioma was found to be similar in two demographically different groups of people. The age of participants in the one cohort was approximately 70 at the time of blood draw, while those in the other cohort were about 40 years old.

"The findings do suggest that individuals with higher exposure to the T. gondii parasite are more likely to go on to develop glioma," said study co-author Anna Coghill, a cancer epidemiologist at the Moffitt Cancer Center in Tampa, Florida. 

"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," she added.

How does one get infected?

According to a report published in Nature, one-third of the general population is infected with T. gondii, with high heterogeneity between countries and regions.

It causes mostly asymptomatic (displaying no symptoms) infection, but mild, flu-like symptoms can occasionally occur during the first few weeks following exposure.  

The primary sources of infection are soil contaminated with cat faeces, undercooked meat, and congenital transmission, notes an article published in The American Journal of Tropical Medicine and Hygiene.

The authors of the study note that although glioma is a relatively rare disease, it is a highly fatal cancer. In 2018, there were an estimated 300 000 global incident cases and 241 000 deaths due to brain and other nervous system cancers. 

Their paper also indicates that the majority (80%) of malignant (cancerous) brain tumours are gliomas, for which the estimated five-year relative survival rate is a low 5%.

They also indicated 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 tumour."

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