You get tapeworms by swallowing their larvae or eggs, almost always through food, water, or accidental contact with contaminated feces. The most common route worldwide is eating undercooked or raw meat or fish that contains tapeworm larvae. Each species of tapeworm has its own path into the human body, but they all require you to ingest something contaminated.
Undercooked Beef and Pork
The two most well-known tapeworm infections come from beef and pork. Cattle and pigs pick up tapeworm eggs while grazing or feeding on contaminated ground. Inside the animal, those eggs develop into larvae that embed themselves in the muscle tissue, forming small cysts. When you eat that meat without cooking it thoroughly, the larvae survive, attach to the wall of your small intestine, and grow into adult tapeworms over about two months.
The beef tapeworm can reach lengths of 15 to 30 feet. The pork tapeworm is smaller but carries a more serious risk: if you swallow its eggs instead of its larvae (more on that below), the infection behaves very differently and can become dangerous. The intestinal version of either infection, called taeniasis, is often mild. Many people don’t realize they’re infected until they notice small, white, rice-shaped segments in their stool two to three months after the initial exposure. Adult tapeworms can live in the intestine for years if untreated.
Raw or Undercooked Fish
A different species of tapeworm, commonly called the fish tapeworm, spreads through raw or undercooked freshwater and certain farmed fish. The larvae live in the flesh and organs of species like trout, salmon, perch, and pike. Wild-caught and farmed fish can both carry the parasite. Research has confirmed larvae in farmed rainbow trout and in wild coho salmon that originally escaped from aquaculture pens.
This is relevant if you eat sushi, sashimi, ceviche, or any preparation where fish isn’t fully cooked. Reputable sushi restaurants mitigate this risk by flash-freezing their fish at temperatures cold enough to kill parasites (the FDA recommends storing fish at -4°F or below for seven days, or freezing it solid at -31°F and holding it for at least 15 hours). Cooking fish to a temperature that kills bacteria also kills parasites. The risk rises when you eat home-prepared raw fish that hasn’t been commercially frozen.
Swallowing Tapeworm Eggs
This route is less common but far more dangerous, and it only applies to the pork tapeworm. When someone already carrying an adult pork tapeworm in their gut passes eggs in their stool, those eggs can contaminate food, water, or surfaces. If another person (or even the same person) swallows those eggs, the outcome is completely different from eating larvae in meat.
Instead of growing into an adult worm in the intestine, the eggs hatch and the tiny embryos burrow through the intestinal wall, enter the bloodstream, and travel to tissues throughout the body. Over 60 to 70 days, they form cysts in muscles, eyes, and the brain. When cysts lodge in the brain, the condition is called neurocysticercosis, and it can cause seizures, severe headaches, and neurological problems. The WHO estimates that between 2.5 and 8.3 million people worldwide are living with neurocysticercosis.
This is why the pork tapeworm is considered a public health concern beyond the individual who eats undercooked pork. A person with an intestinal infection sheds eggs that can infect others through poor hand hygiene, contaminated produce, or unsafe water.
Pets and Fleas
Dogs and cats commonly carry their own species of tapeworm, and humans, particularly young children, occasionally get infected. The route is indirect: the tapeworm’s lifecycle passes through fleas. Flea larvae swallow tapeworm eggs, and as the flea matures, the tapeworm larva develops inside it. When a child (or adult) accidentally swallows an infected flea, typically during close face-to-face contact with a pet or by putting contaminated hands in their mouth, the larva is released in the intestine and grows into an adult worm.
This type of infection is generally harmless and easy to treat. It’s most common in households where pets have active flea infestations. Keeping pets on regular flea prevention is the most effective way to eliminate this risk.
Contaminated Soil, Water, and Produce
A less familiar but serious route involves a group of tapeworms that cycle between dogs and livestock. Dogs shed microscopic eggs in their feces, and those eggs can persist in soil, on vegetables, and in water sources. Humans become infected by ingesting the eggs, whether from unwashed produce grown in contaminated soil, untreated water, or direct contact with an infected dog’s fur or feces.
Unlike the intestinal tapeworms from meat, these eggs develop into large, fluid-filled cysts in internal organs, most often the liver and lungs. This condition, called hydatid disease, is most prevalent in rural communities where dogs live alongside livestock and have access to raw offal. It’s a particular concern in parts of South America, the Mediterranean, Central Asia, and East Africa.
Why Some People Are at Higher Risk
Geography and food culture play a large role. Tapeworm infections from beef and pork are most common in regions where meat inspection is limited, sanitation infrastructure is underdeveloped, and dishes traditionally feature raw or lightly cooked meat. Fish tapeworm infections cluster around cultures with strong traditions of eating raw freshwater fish, including parts of Scandinavia, South America, and East Asia.
Travelers to endemic areas face increased risk if they eat street food or dishes prepared with local meat or fish that may not have been thoroughly cooked. People living in close contact with free-ranging dogs and livestock, especially in farming communities without veterinary deworming programs, are more exposed to the egg-borne forms that cause cyst disease.
How to Protect Yourself
Cooking meat and fish thoroughly is the single most effective prevention. For beef and pork, using a meat thermometer to verify the interior reaches a safe temperature kills any embedded larvae. For fish you plan to eat raw, commercial-grade freezing at -4°F for seven days, or at -31°F for 15 to 24 hours, destroys parasites. A standard home freezer may not reach these temperatures reliably.
Beyond cooking, the other key protections are straightforward:
- Wash produce thoroughly, especially in areas where crops may be irrigated with untreated water or grown in soil fertilized with animal waste.
- Practice consistent hand hygiene, particularly after using the bathroom, handling raw meat, or touching animals.
- Control fleas on pets with veterinarian-recommended preventatives to break the transmission cycle for the dog and cat tapeworm.
- Deworm dogs regularly in rural or farming settings where they might scavenge raw meat or organs from livestock.
- Avoid untreated water in regions where sanitation is unreliable.
Most intestinal tapeworm infections are easily treated with a single course of antiparasitic medication that kills the worm so it passes naturally. The tissue-invading forms, neurocysticercosis and hydatid disease, are more complex to manage and sometimes require surgical intervention, which is why prevention matters far more than treatment for those types.