Many people with intestinal tapeworm infection don't have symptoms. If you do have problems from the infection, your symptoms will depend on the type of tapeworm you have and its location. Invasive tapeworm infection symptoms vary depending on where the larvae have migrated.

Intestinal infection

Signs and symptoms of intestinal infection include:

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

Invasive infection

If tapeworm larvae have migrated out of your intestines and formed cysts in other tissues, they can eventually cause organ and tissue damage, resulting in:

• Headaches
• Cystic masses or lumps
• Allergic reactions to the larvae
• Neurological signs and symptoms, including seizures

A tapeworm infection starts after ingestion of tapeworm eggs or larvae.

• Ingestion of eggs. If you eat food or drink water contaminated with feces from a person or animal with tapeworm, you ingest microscopic tapeworm eggs. For example, a pig infected with tapeworm will pass tapeworm eggs in its feces, which gets into the soil.

If this same soil comes in contact with a food or water source, it becomes contaminated. You can then be infected when you eat or drink something from the contaminated source.

Once inside your intestines, the eggs develop into larvae. At this stage, the larvae become mobile. If they migrate out of your intestines, they form cysts in other tissues, such as your lungs, central nervous system or liver.

• Ingestion of larvae cysts in meat or muscle tissue. When an animal has a tapeworm infection, it has tapeworm larvae in its muscle tissue. If you eat raw or undercooked meat from an infected animal, you ingest the larvae, which then develop into adult tapeworms in your intestines.

Adult tapeworms can measure more than 80 feet (25 meters) long and can survive as long as 30 years in a host. Some tapeworms attach themselves to the walls of the intestines, where they cause irritation or mild inflammation, while others may pass through to your stool and exit your body.

Factors that may put you at greater risk of tapeworm infection include:

• 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.
• Traveling 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.
• Living in endemic areas. In certain parts of the world, exposure to tapeworm eggs is more likely. For instance, your risk of coming into contact with eggs of the pork tapeworm (Taenia solium) is greater in areas of Latin America, China, sub-Saharan Africa or Southeast Asia where free-range pigs may be more common.

Intestinal tapeworm infections usually don't cause complications. If complications do occur, they may include:

• Digestive blockage. If tapeworms grow large enough, they can block your appendix, leading to infection (appendicitis); your bile ducts, which carry bile from your liver and gallbladder to your intestine; or your pancreatic duct, which carries digestive fluids from your pancreas to your intestine.
• Brain and central nervous system impairment. Called neurocysticercosis (noor-o-sis-tih-sur-KOE-sis), this especially dangerous complication of invasive pork tapeworm infection can result in headaches and visual impairment, as well as seizures, meningitis, hydrocephalus or dementia. Death can occur in severe cases of infection.
• Organ function disruption. When larvae migrate to the liver, lungs or other organs, they become cysts. Over time, these cysts grow, sometimes large enough to crowd the functioning parts of the organ or reduce its blood supply. Tapeworm cysts sometimes rupture, releasing more larvae, which can move to other organs and form additional cysts.

A ruptured or leaking cyst can cause an allergy-like reaction, with itching, hives, swelling and difficulty breathing. Surgery or organ transplantation may be needed in severe cases.