ACS Research Highlights

Parasite in Food and Water May Increase Risk of Brain Cancers

A CPS-II Nutrition Cohort Study:Researchers showed that a parasite most commonly found in undercooked meat may lead to certain brain cancers.

The Challenge 

Brain tumors are rare, and there are many different types. The most common brain tumors are gliomas, and they tend to have a low 5-year survival rate. The causes of brain tumors, including gliomas, remain largely unknown. Few studies have been able to identify modifiable risk factors, but some suggest a potential association between certain infections and increased risk. One of those infections is caused by the microscopic parasite Toxoplasma gondii (T gondii).

T gondii is a common parasite that infects warm-blooded animals, including humans. Infections most often occur from:

  • Eating undercooked meat or shellfish from infected animals.
  • Eating unwashed fruits and vegetables.
  • Drinking contaminated water.
  • Accidentally swallowing the parasite through contact with cat feces that contain it.

Even though many animals and people around the world may be infected with T gondii, most people with healthy immune systems aren’t affected by it and don’t have any symptoms or illness.

T gondii infections in the brain have, however, been linked with changes in cognitive function and behavioral disorders in both animals and humans. Earlier studies with groups of people have also suggested a link between gliomas and T gondii infections, but studies looking at individuals are lacking.

The Research 

James Hodge, JD, MPH, and his American Cancer Society (ACS) colleagues recently led the first prospective cohort study to provide evidence of an association between T gondii infection and the risk of glioma brain tumors.

Our findings suggest that infection with the parasite Toxoplasma gondii may play a role in development of glioma. If confirmed by future research, this would represent a breakthrough in finding a modifiable risk factor for this particularly insidious form of brain cancer.”

James Hodge, JD, MPH

Population Science

American Cancer Society

He and his team analyzed blood samples given by participants in the ACS Cancer Prevention Study-II Nutrition Study when they were cancer free. They also studied samples from a Norwegian biorepository in collaboration with researchers from the H. Lee Moffitt Cancer Center and Research Institute in Tampa. To identify those infected with the parasite, they looked for two antibodies to T gondii, which would have occurred in response to the presence of the parasite.

During the time the Nutrition Cohort was followed, 50 CPS-II Nutrition Study participants were diagnosed with gliomas, and 323 people were diagnosed in the Norwegian cohort.

When Hodge and his team compared glioma cases to cancer free participants, they found that those who had T gondii antibodies in their blood were more likely to develop a glioma in the 13 years after the blood was collected.

How to Prevent Infection

To prevent infection with T gondii, follow these tips from the Centers for Disease Control (CDC):

  • Freeze meat for several days before cooking.
  • Don’t eat raw or undercooked oysters, mussels, or clams.
  • Cook food to safe temperatures: 145° F for whole cuts of meat, 160° F for ground meats, and 165° F for whole or ground poultry.
  • Wash and peel fruits and vegetables before eating.
  • Wash cutting boards, dishes, counters, utensils, and hands with soapy water after touching raw meat, poultry, seafood, and unwashed fruits and vegetables.
  • Wear gloves when gardening because soil or sand may be contaminated with cat feces that contain T gondii. Wash hands with soap and water after contact with soil or sand.
  • Clean cat litter boxes daily. The T gondii parasite doesn’t become infectious until 1 to 5 days after it’s shed in cat feces. Wash hands after cleaning a litter box.


To confirm the possible role of T gondii infection in causing gliomas, more studies are needed with larger numbers of people with gliomas.

Why It Matters 

If Hodge’s results are replicated in future studies, we could be a step closer toward identifying a modifiable risk factor for glioma.