Tapeworms are parasitic segmented flatworms of the class Cestoda. This type of parasite usually requires two different hosts to complete their life cycle. The adult tapeworm inhabits the gastrointestinal tract of the primary host. The intermediate host incubates the larval form of the parasite within its muscles and internal organs. The primary host usually becomes infected by ingestion of undercooked or raw meat from an infected intermediate host. The intermediate host usually acquires its infection by ingesting food containing tapeworm eggs from a primary host’s feces.
The dwarf tapeworm Hymenolepis species is the smallest tapeworm to use humans as primary hosts. The intermediate hosts for Hymenolepis species are beetles with human infection occurring from ingestion of water contaminated by beetles. Rats also act as primary hosts, and the beetles acquire the infection by eating rat’s feces. There are two species of Hymenolepis capable of infecting humans H. nana and H. diminuta. H. nana is unusual because it can complete its life cycle within man without using an intermediate host.
Numerous cases of H. species infection are asymptomatic with the patient only realizing the have worms if the see small segments in their feces. If a patient develops a symptomatic infection, they may experience a loss of appetite, nausea, diarrhea, weakness and abdominal pain.
There are two species of Taenia tapeworm capable of using humans as primary hosts. These are Taenia saginata or the beef tapeworm, which uses cattle as intermediate hosts and Taenia solium or the pork tapeworm, which uses pigs as intermediate hosts. Adult T. saginata worms are 12-25 feet in length while T. solium are shorter growing 3-6 feet in length. Symptoms with Taenia infections are similar to those seen in dwarf tapeworm infection with asymptomatic cases being common. Some patients experience malnutrition and malabsorption of food when infected with Taenia species.
If someone ingests the eggs of T. solium, they may develop the larval form of the parasite in their tissues. This form of infection, known as cysticercosis, is frequently asymptomatic. However, larval cysts developing in the brain (neurocysticercosis) may lead to a number of neurological symptoms depending on the number and location of the cysts. Symptoms of neurocysticercosis range from headaches and mood changes through to seizures and strokes.
Rarely another Taenia species may cause infections in man. This is T. multiceps, which causes coenurosis a space-occupying lesion in the central nervous system and subcutaneous tissues. The symptoms of coenurosis depend on the sites of the lesions.
The fish tapeworm, Diphyllobothrium latum, uses a number of species fish including turbot, pike or salmon as its intermediate hosts. While they can grow to 30 feet in length, adult D. latum worms are usually only 3-7 feet long. As with the other tapeworm infections, asymptomatic infections are common with D. latum. Where symptoms do occur they resemble those of Taenia infections.
Unfortunately, a large D. latum tapeworm can block its host’s intestine. Such intestinal blockages are painful and potentially fatal and they require immediate surgical treatment.
Another complication seen in infections with this type of parasite is anemia. Vitamin B12 is important in the production of hemoglobin. D. latum frequently uses much of the vitamin B12 within its host’s diet leading to B12 deficiency and anemia.
Dipylidium caninum is the dog and cat tapeworm that uses fleas as an intermediate host. Occasionally this parasite may infect humans, usually children in close contact with an infected animal. Infections with D. caninum are usually asymptomatic but mild gastrointestinal symptoms sometimes occur.
A tapeworm, which occasionally forms larval cysts in humans, is Echinococcus species. Echinococcus tapeworms use a number of carnivores such as foxes, wolves, coyotes and cats as their primary hosts. Human echinococcosis or hydatid disease involves a slow growing cyst usually in the liver. While frequently asymptomatic for many years, this condition is potentially fatal as rupture of the cyst causes anaphylactic shock. The most common symptom, caused by a hydatid cyst growing in the liver, is a pain the upper right quadrant of the abdomen.
Another tapeworm found producing cysts in humans is Spirometra species, which causes sparganosis a cystic condition causing subcutaneous edema. The parasite may also cause lesions in the patient’s muscles, eyes, urogenital system, abdominal organs and occasionally the central nervous system.
Most primary tapeworm infections are diagnosed by examination of fecal samples. Sometimes worm segments are visible in the sample otherwise the characteristic eggs maybe detected microscopically. Larval infections of tissues require the detection of antibodies to the parasite in a blood sample for diagnosis with further tests, such as an MRI, to localize the cysts.
A number of treatment options are available for patients with tapeworm infections. Consultation with a qualified medical practitioner will ensure the correct treatment for any particular tapeworm infection. Albendazole (Albenza), Paromomycin (Humatin), Praziquantel (Biltricide), Praziquantel (Biltricide) and Mebendazole (Vermox) are all active against adult tapeworms. Albendazole (Albenza) is the drug of choice in treating echinococcosis and cysticercosis.
Patients with neurocysticercosis may require anticonvulsant therapy to prevent seizures. Diazepam (Valium) is commonly used for such therapy.
Patients with anaemia caused by a D. latum infection may require vitamin therapy. Cyanocobalamin (Cobex, Berubigen, Crystamine) helps rectify the patient’s vitamin B12 deficiency.
Surgical removal of cysts is required for treating sparganosis and coenurosis and sometimes echinococcosis
Medical Microbiology. 4th edition. Baron S, editor. 1996 – Chapter 89 Cestodes by Donald Heyneman