Parasites that Can Lead to Cancer
Cancer is not a parasite, but certain parasitic worms can increase the risk of some types of cancer.
What is a parasite?
A parasite is an organism that lives on, in, or with another organism (host). It gets its food to grow from the host organism. Parasites are not common in the United States, but they can be a concern for people who live in or travel to other parts of the world.
Most people have no symptoms of a parasite infection. Depending on the parasite, some people might have stomach cramps, diarrhea, nausea, and vomiting.Treatment options include antiprotozoal, anthelmintic, and certain antibiotics such as nitroimidazoles.
Parasites and cancer
The International Agency for Research on Cancer (IARC) has classified 3 parasitic infections as known carcinogens (cancer-causing agents) in humans.
Opisthorchis viverrini and Clonorchis sinensis are liver flukes that can affect the bile ducts after a person eats raw or undercooked freshwater fish containing one of these parasites. Over time, these parasites can cause chronic inflammation, irritation, and damage, which increases the risk of bile duct cancer. These infections are most common in parts of East Asia and are rare in other areas, including the US.
Schistosoma haematobium is a parasite found in freshwater in some parts of the Middle East, Africa, and Asia. Infection with this parasite, called schistosomiasis, has been linked to an increased risk of bladder cancer. Researchers are also studying whether it might be linked to other types of cancer, such as certain lymphomas. More research is needed to know for sure.
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The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as editors and translators with extensive experience in medical writing.
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Centers for Disease Control and Prevention. About Parasites. Accessed at https://www.cdc.gov/parasites/about/index.html on March 3, 2026.
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Last Revised: August 12, 2026
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