According to merckmanuals.com, there are three main types of tapeworm that infect humans. The beef tapeworm, (Taenia saginata) pork tapeworm, (Taenia solium) and fish tapeworm (Diphyllobothrium latum) can all make their homes in the human body, causing various symptoms depending on the severity of the infection. Pork and beef tapeworms inhabit the intestines and can grow 15 to 30 feet in length.
Tapeworms are acquired primarily through eating raw or undercooked meat. Beef, pork, or freshwater fish may contain cysts with tapeworm larva, but as long as the meat is thoroughly cooked the larva will be killed and a tapeworm infection will not be possible from eating that meat. Tapeworms can also be picked up through contact with animal or human feces.
Symptoms of a tapeworm infestation in humans depend on the severity of the infestation. According to both merckmanuals.com and mayoclinic.com, an infestation involving a grown tapeworm in the intestines may produce no symptoms whatsoever, but may produce nausea, diarrhea, or loss of appetite. The fish tapeworm may cause anaemia, because it absorbs vitamin B12, which the body needs to form mature red blood cells. A victim of a tapeworm infestation may also notice small bits of the tapeworm (protoglottids) passed with the stool. It is these small pieces that contain tapeworm eggs. More invasive infestations, where tapeworm larva get into the blood stream through the intestine, and travel to form larva cysts in the muscles, organs (including the brain and eyes), or under the skin, may produce headaches, pain, swelling, confusion, tremors, seizures, muscle weakness, paralysis, or blindness. Even these invasive cases, however, may be symptomless.
Tapeworms in the intestine are treated with a single dose of the antiparasitic drug praziquantel. Cysts of tapeworm larva are generally not treated unless the cysts are in the brain, as they do not pose a danger to human health. When in the brain, larval cysts are treated with antiparasitic drugs, and sometimes corticosteroids to reduce inflammation. If symptoms of larval cysts elsewhere are troublesome, corticosteroids may be used for those elsewhere. Corticosteroid drugs are never used to treat cysts in the eyes or spinal cord, because they may cause dangerous swelling in those areas.
The best treatment for tapeworm is actually prevention. Cooking beef, pork, and freshwater fish thoroughly, and practicing proper handwashing goes a long way towards preventing infestation.