Tapeworm infection usually occurs when you eat food or drink water contaminated with tapeworm eggs or larvae. Most people infected with tapeworm are unaware they're carrying them. Tapeworms occur in humans in one of two forms. If ingested as eggs, they may develop into larvae that migrate out of the intestines and form cysts in other tissues such as the lungs or liver. These cysts can cause serious problems. Or, if ingested as larvae, they typically develop into adult tapeworms in the intestines, which usually cause few or no symptoms.

A tapeworm infection that's confined to your intestines is easily treated with oral medications, and the prognosis for eradication is good. However, when the disease has migrated to other parts of your body, treatment is more difficult and untreated cases can be life-threatening.

The good news is that you can help prevent tapeworm infection with good personal hygiene, such as washing your hands before eating, and avoiding eating raw or undercooked meats.

Often no signs or symptoms
Most people who are infected with tapeworm don't show symptoms.

Signs and symptoms of intestinal infection
Most likely, you won't have any signs or symptoms with an intestinal infection. It's possible you might notice segments of the adult tapeworm (proglottids) in your stool. Other possible signs and symptoms include:

• Nausea
• Weakness
• Loss of appetite
• Abdominal pain
• Diarrhea
• Weight loss and inadequate absorption of nutrients from food

Signs and symptoms of invasive infection
If tapeworm larvae have moved out of your intestines and formed cysts in other tissues, it can cause organ and tissue damage, resulting in:

• Fever
• Cystic masses or lumps
• Allergic reactions to the larvae
• Bacterial infections
• Neurological symptoms or seizures if the brain is involved

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Beef tapeworm

In humans, tapeworm disease is most commonly caused by one of several tapeworm species: the pork tapeworm (Taenia solium), beef tapeworm (Taenia saginata), dwarf tapeworm (Hymenolepis nana), and fish tapeworm (Diphyllobothrium latum) from raw freshwater fish.

You usually get tapeworm infection by ingesting tapeworm eggs or larvae.

• Ingestion of eggs. Tapeworm eggs are generally ingested through food, water or soil contaminated with human or animal (host) feces.

  For example, if a pig is infected with a tapeworm, it may pass eggs or segments (proglottids) of the adult tapeworm through its feces into soil. Each segment contains thousands of microscopic tapeworm eggs. You can then ingest these eggs by eating food contaminated with the feces. Once you consume the eggs, they develop into larvae, which can migrate out of your intestines and form cysts in other tissues such as your lungs or liver. This type of infection is not common with beef or fish tapeworms, but can occur with the pork tapeworm — called cysticercosis — and can also occur with dog and sheep tapeworms — called echinococcosis.

• Ingestion of larvae cysts in meat or muscle tissue. You can also get tapeworm infection by eating raw or undercooked meat from an animal or a fish that has the larval form of the tapeworm (cysts) in its muscle tissue. Once you ingest them, the larvae then develop into adult tapeworms in your intestines.

  Adult tapeworms can measure up to 50 feet long and can survive as long as 20 years. Some tapeworms attach themselves to the walls of the intestine, where they cause irritation or mild inflammation, while others may pass through to your stool and exit your body.

Unlike other tapeworms, the dwarf tapeworm can complete its entire life cycle — egg to larva to adult tapeworm — in one host. This is the most common tapeworm infection in the world and can be transmitted between humans.

While being treated for certain tapeworm infections, you can reinfect yourself by ingesting tapeworm eggs shed by the adult worm into your stool. That's why you should take care to wash your hands after using the toilet.

Certain considerations may put you at greater risk of tapeworm infection, such as:

• Poor hygiene. Infrequent washing and bathing increases the risk of accidental transfer of contaminated matter to your mouth.
• Exposure to livestock. This is especially problematic in areas where human and animal feces are not disposed of properly.
• Frequent travel to developing countries. Infection occurs more frequently in areas with poor sanitation practices.
• Eating raw or undercooked meats. Improper cooking may fail to kill tapeworm eggs and larvae contained in contaminated pork or beef.

If you experience any of the signs or symptoms of tapeworm infection, you should seek medical attention. Also contact your doctor if you believe you've been exposed to food or water contaminated with tapeworm.

You may notice infection by checking your stool for parts of the adult tapeworm. But it's likely you'll need your doctor to check your stool or send samples to a laboratory for testing. A laboratory may use microscopic identification techniques to check for eggs or tapeworm segments in your feces. The lab may need to collect two to three samples over a period of time to detect the parasite, since eggs and tapeworm segments are released irregularly into the stool.

For tissue-invasive infections, your doctor may also test your blood for antibodies your body may have produced to fight tapeworm infection. The presence of these antibodies indicates tapeworm infestation. Certain types of imaging, such as CT or MRI scans, also may suggest the diagnosis.

The consequences of tapeworm infection can vary, depending on what species of tapeworm you're infected with.

Beef tapeworm usually not harmful
The beef tapeworm can be relatively harmless, since it lives only in your intestine and is easily treated with medication.

Pork, dog and sheep tapeworms can cause serious complications

• Cysticercosis. Ingesting eggs of the pork tapeworm can result in infection by the larval form of the organism, called cysticercosis. These larvae can migrate to tissues and organs throughout your body and develop into lesions or cysts. Lesions and cysts grow slowly over many months and can disrupt normal organ function, host a secondary infection or even rupture.
• Neurocysticercosis. This is an especially dangerous complication of the pork tapeworm infection. This disease affects the brain and central nervous system, resulting in headaches and visual impairment, as well as seizures, meningitis or dementia. Death can occur in severe cases of infection.
• Echinococcosis. This infection is a complication that can follow the ingestion of the eggs of the echinococcus tapeworm, most commonly found in dogs or sheep. In humans the larvae that develop can migrate to organs — often the liver — and cause large cysts to develop. These cysts can place pressure on nearby blood vessels, hindering circulation or causing the blood vessels to rupture. Surgery or liver transplantation may be required in severe cases of infection.

Medications that kill tapeworms
The most common treatment for tapeworm infection involves oral medications that are toxic to the tapeworm. These drugs include praziquantel (Biltricide) or albendazole (Albenza), as well as niclosamide, although this drug is not available in the United States. The medication prescribed depends on the species of organism and site of infection involved.

The medications are poorly absorbed by your digestive tract and generally work by dissolving or attacking the adult tapeworm. Be aware that these drugs target the adult tapeworm, not the eggs, so take care to avoid reinfecting yourself. Always wash your hands after using the toilet and before eating.

Stool samples are generally checked at one month or three months after you've finished taking your medication, depending on what species of tapeworm you have. Successful treatment should render your stool free of tapeworm eggs, larvae or proglottids. The success rate is greater than 95 percent in people who receive appropriate treatment.

Anti-inflammatories if you have cysts
In cases in which the tapeworm infection has migrated to tissues outside your intestine, your doctor may prescribe an anti-inflammatory steroid to reduce any swelling caused by the development of cysts.

Surgery if you have life-threatening cysts
Surgery may be required to remove cysts that have developed in your liver, lungs or other organs, and organ transplantation may be your last resort in some cases.

To prevent tapeworm infection:

• Wash your hands with soap and water before eating or handling food and after using the toilet.
• When traveling in areas where tapeworm is found, wash and cook all fruits and vegetables with safe water before eating.
• Eliminate livestock exposure to tapeworm eggs by properly disposing of animal and human feces.
• Thoroughly cook meat at temperatures of at least 150 F (66 C) to kill tapeworm eggs or larvae.
• Freeze meat for at least 12 hours and fish for at least 24 hours to kill tapeworm eggs and larvae.
• Avoid eating raw or undercooked pork, beef and fish.
• Promptly treat dogs infected with tapeworm.

If you're infected with tapeworm, seek medical attention. Take medications as directed and talk to your doctor about any changes in your condition.

During treatment, take care to avoid recontaminating yourself or spreading your infection to others. Wash your hands frequently, especially after going to the toilet and before handling food. Avoid touching your mouth with your unwashed hands.