Causes and Risk Factors of Tapeworm Infections

Infections with tapeworms are a risk of eating undercooked or raw meat or fish

Most infections with tapeworms, also called taeniasis, come from eating undercooked or raw meat, pork, or fish. A second less common cause is when an infected person transmits the illness to others. This can happen, for example, by not washing hands properly after going to the bathroom and then cooking food. People who live in close proximity to livestock or free-range animals and/or have poor sanitation have a greater risk of developing a tapeworm infection.

Tapeworm infections are more common in developing areas of the world where sanitation is poor and people may eat undercooked meats. Thus, traveling to these areas is another risk factor, and treating the infection after diagnosis is important to prevent further spread.

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How Infection Occurs

Tapeworms are often referred to by the type of meat they infect: Taenia saginata (beef tapeworm), Taenia solium (pork tapeworm), and Taenia asiatica (Asian tapeworm, which also infects pork). Diphyllobothrium latum is a type of broad tapeworm that infects freshwater fish. In the United States, transmission of pork tapeworm (T solium) is the most concern among recent immigrants. Infection with this tapeworm can cause a serious disorder of the brain called neurocysticercosis.

Tapeworms start their life cycle as an egg. Eggs can live outside a human or animal host for days or months and may contaminate feed or vegetation, which then may be eaten by livestock (pigs or cows). The eggs hatch inside the animal and then the young tapeworms (cysticerci) move from the intestines into the muscle tissue.

Cysticerci can survive in the animals' muscle tissue for years. If the animal is then harvested and eaten by humans without being thoroughly cooked to kill the tapeworms, the ingested cysticerci can take up residence in the human intestine.

It takes two months for cysticerci to grow into an adult tapeworm while living in in the human intestine. The adult tapeworm then attaches to the wall of the small intestine and can live there for years (as long as 30 years). An adult tapeworm produces proglottids, which is a segment of the worm that has male and female reproductive parts. The proglottids become pregnant with eggs and break off from their parent worm, which is still living in the intestine. The pregnant worm passes through the digestive system and out of the anus with a bowel movement.

After leaving the body with stool, the tapeworm eggs are released, where they can then be ingested by another animal or human, starting the process over again.

Infection From Meat

The primary way that humans can contract a tapeworm is from eating meat, pork, or fish that is infected with tapeworms. If the animal was infected the meat will harbor larva or eggs.

While properly cooking and/or freezing meats can kill tapeworms, when any cut of meat is suspected to be infected with any pathogen the best course of action is to discard it. Cooking meats well helps reduce the risk that it contains any live parasites, but raw meat, poultry, and fish comes with no such protection and eating them should be avoided.

Undercooked Fish

Broad tapeworms that infect fish are most frequently found in freshwater species such as salmon, trout, perch, and walleyed pike. Fish that are pickled, smoked, or “lightly salted” may not be cooked or treated in a way that will kill these tapeworms. Infection with this type of tapeworm is more commonly found in fish originating from the Northern hemisphere.

Eating When Traveling

Traveling to less developed countries may put travelers at risk of contracting tapeworms because infection is more common outside the United States. It’s important to ensure that fish and meats are cooked thoroughly and that other food (even fruits and vegetables) are prepared with water that is boiling or has been chemically treated to kill pathogens. If you have your doubts, avoid the dish.

Infection From Humans

Humans can also be infected with tapeworms through other humans, though this is less common. A person who is infected will pass eggs from the tapeworm in their stools. If an infected person touches their stool during a bowel movement, tapeworm eggs may wind up on their hands and then be transmitted to other surfaces or food.

Correct hand washing with soap and warm water can remove these eggs, but if an infected person doesn’t (or is unable to) do that after going to the bathroom, they can spread the eggs to other people.

Prevention

You can take steps to kill tapeworms if you properly freeze and cook your food.

Meats

Cooking meats properly and freezing them at the proper temperatures can help kill any tapeworms they might be harboring. Meat should be cooked until the center is no longer pink and the juices run clear. Further, letting meat rest for at least three minutes before serving it will also help kill any tapeworms because the meat continues to cook while it is resting.

The FDA recommends these guidelines:

  • Freezing meat or pork at -4 degrees F (-20 degrees C) for 7 days
  • Cooking ground meat and poultry to an internal temperature of at least 160 degrees F (71 degrees C) 
  • Cooking whole cuts of meat to an internal temperature of at least 145 degrees F (approximately 63 degrees C)

Fish

Fish should be cooked until it is flaky and is a solid color. The FDA recommends that fish should also be cooked to an internal temperature of 145 degrees F (approximately 63 degrees C). Freezing at least -4 degrees (-20 degrees C) for a week (7 days) will also kill tapeworms. Lower temperatures can be used for a shorter time to kill tapeworms, including:

  • Freezing until solid at -31 degrees F (-35 degrees C) or below, and storing at this temperature or below for 15 hours
  • Freezing until solid at -31 degrees F (-35 degrees C) and then storing for 24 hours at -4 degrees (-20 degrees C)
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Article Sources
  • Global Health – Division of Parasitic Diseases. "Diphyllobothrium latum (and other species) FAQs." Centers for Disease Control and Prevention. 10 Jan 2012. 
  • Global Health – Division of Parasitic Diseases. "Taeniasis FAQs." Centers for Disease Control and Prevention. 10 Jan 2013.
  • Global Health – Division of Parasitic Diseases. "Taeniasis Biology." Centers for Disease Control and Prevention. 10 Jan 2013.
  • U.S. Department of Health and Human Services. "Safe Food Handling: What You Need to Know.” U.S. Food and Drug Administration. 30 Nov 2017.