The tapeworm (cestoda) is a flatworm (plathelminths). Only a few of over 3,000 specialized species attack humans. Contaminated food or close contact with infected animals can lead to infection with tapeworm eggs or larvae. The pathogens are absorbed through the mouth. The parasites then become unwanted subtenants in the digestive tract. Not all hosts experience symptoms of tapeworm infestation. Unspecific signs of illness such as abdominal pain, nausea, abnormal sensations and changes in stool behavior occur in a third of the patients. Worldwide, ten million people are infected with tapeworms every year. Thanks to high hygiene standards, worm diseases affect less than 0.01 percent of the population in Germany. Surveys by the veterinary laboratory Freiburg in 2011 document an infestation of one percent among German pets. According to their estimates, the number of unreported cases is far higher.
How do you get a tapeworm?
Tapeworms are survivors who are known for changing hosts. Like chameleons, the parasites integrate into the tissue. Some have remained undetected for decades. More than ten different tapeworm species use humans as intermediate or final hosts. The most common type of contact is via ingestion. Half-raw meat and fish products contain larvae or encapsulated worm stages that mature into the adult tapeworm in the human intestine. As soon as the parasite reaches sexual maturity, it fertilizes itself. As a result, tapeworm eggs in human stool reach the sewage system. In heavy rain, the canals become overloaded, causing pastures and fresh water to come into contact with contaminated wastewater. And the cycle starts over.
In addition to consumption raw meat and fish products, unwashed raw food and contaminated fruits can be a source. The same applies to poor hygiene after contact with excrement or infected animals. The development cycle differs depending on the type of tapeworm.
Fish tapeworm (Diphyllobothrium latum)
Fish tapeworm infestations have decreased worldwide in the recent past. In Germany, the risk of infection from contaminated fish products is low thanks to strict regulations for fish processing. Risks exist when traveling in epidemic areas such as North America and Scandinavia. A wave of sushi led to increased cases in America in the 1980s and 1990s.
Mature worm segments (proglottids) reach freshwater in the feces of infected end hosts. Tapeworm eggs mature into larvae in eight to twelve days. The first intermediate hosts are water crabs and small fish. The second larvae, along with these hosts, are eaten by larger fish. Only now do contagious pathogens emerging from the fish tapeworms.
Fish-eating mammals ingest the infectious larvae with food. In addition to cats and dogs, humans are considered to be possible end hosts for the fish-specific tapeworm. People in regions like Alaska have shared their gut in the past most frequently with fish tapeworms. If this form of tapeworm can be detected in stool, it is called diphyllobothriasis.
Beef tapeworm (Taenia saginata) & pork tapeworm (Taenia solium)
Half-raw meat from infected cattle and pigs contains encapsulated worm precursors (Finns) of beef and pork tapeworm. Human stomach acid dissolves the capsule when consumed. The worm precursors then mature into egg-laying worms. Veterinary meat inspection is said to protect against beef and pork tapeworms in Germany. Such regulations do not exist in developing countries. According to the Robert Koch Institute, the incidence of illness is therefore closely related to origin and eating habits.
Dwarf tapeworm (Hymenolepis nana) & rat tapeworm (Hymenolepis diminuta)
The Hymenolepis nana is a special tapeworm. Lengths of four centimeters make the parasite the smallest species. At the same time, the parasite is the most common tapeworm in children. This group of patients often touches infected people or contaminated objects and then puts their hands in their mouths. This leads to smear infection. Self-infection can occur from contact with one's own feces.
The dwarf tapeworm does not need intermediate hosts. In addition to humans, the parasite uses rodents as final hosts. The associated clinical picture is considered hymenolepiasis, which occurs most often in warm countries. A distinction must be made between this and the rat tapeworm, which accidentally infects humans and uses insects as intermediate hosts.
Small dog tapeworm (Echinococcus granulosus) & small fox tapeworm (Echinococcus multilocularis)
Fox and dog tapeworm can lead to life-threatening echinococcosis in humans. Therefore infections in Germany are subject to compulsory registration. In 2014, 112 Germans became infected with echinococci, according to the Robert Koch Institute. Baden-Wurttemberg and Bavaria are considered risk areas. Humans are mistaken intermediate hosts for both types of tapeworm. The real intermediate hosts are rodents and hoofed animals.
Echinococci are cold-resistant and stay infectious for months. The most relevant risk of infection is the close contact with contaminated animals in addition to the consumption of contaminated forest fruits. The larvae in the body of the intermediate host attack organs such as the liver via the blood and lymph channels. They proliferate there to protect themselves from defense cells. This results in tapeworm cysts and malignant tumors that shape the clinical picture of cystic and alveolar echinococcosis.
What are the symptoms of a tapeworm?
According to the Robert Koch Institute, a third of all tapeworms cause symptoms such as:
- Burrowing in the umbilical region
- Itching in the buttocks area
- Stomach pain
- Nausea and vomiting
- Constipation & diarrhea
- Body aches
- Loss of appetite
- Weight loss
- Discomfort during bowel movements
Often it is just worm parts in the stool that make patients recognize the tapeworm. For some tapeworm species, there is a decades-long incubation period between transmission and the first symptoms. If the pathogens infect other organs via the bloodstream, the clinical picture varies depending on the target organs. In addition to yellowing of the skin, anemia, neurological disorders and blood admixtures in the urine can occur.
How can a tapeworm be diagnosed?
How doctors identify a tapeworm depends on the type of parasite. Deficiency symptoms with regard to nutrients such as vitamin B12 are unspecific symptoms with tapeworm infestation. The stool specimen gives more specific indications of tapeworm infection. Diagnoses of certain types of worms are partly possible through a blood sample. With the fox and dog tapeworm, specific antibodies are shown in the Western blot and ELISA test.
To detect the beef tapeworm, eggs can be enriched by microscopic examination. In this case, an unfixed squeeze preparation of the worm segments serves to differentiate individual worm species from other tapeworms. The number of uterine branches allows classification.
In case of organ involvement,** imaging** is required. Echinococcosis can be palpated and then recorded using ultrasound, computer or magnetic resonance imaging.
What does tapeworm treatment look like?
The severity and type of infestation determine how patients get rid of their tapeworm. Different drugs help against parasites like tapeworm. Treatments focus on either blocking nutrient absorption or completely paralyzing tapeworms.
Worm remedies (anthelmintics) such as niclosamide, praziquantel and mebendazole are used for this. These are taken in tablet or juice form. After successful treatment, patients excrete the dead parasites via the intestine.
For tapeworm cysts and tumors, surgical removal is indicated. If patients are not operable, they are given alternative benzimidazoles such as mebendazole and albendazole. If the removal is incomplete, long-term treatment with worming agents is required.
Studies from 2013 opened the discussion about the use of cancer drugs for future tapeworm treatment.
Are tapeworms always harmful?
Tapeworms were administered for weight loss in the United States in the 20th century. In this controversial Tapeworm Diet, patients use the parasite as a natural fat blocker. Experts do not recommend this harmful diet measure.
In the meantime, the interest of the pharmaceutical industry has gone beyond tapeworms to lose weight. Corresponding studies around the world are concerned with the idea of keeping over-reactions of the immune system at bay by tapeworms. The uninvited subtenants are currently under discussion as future medications for the treatment of autoimmune diseases such as multiple sclerosis, Crohn's disease and allergies.
Bundesinstitut für Risikobewertung (2001): Rinderbandwurm. Retrieved from http://www.bfr.bund.de/cm/350/rinderbandwurm.pdf (18.06.2018, 3:05 p.m.).
Bundesinstitut für Risikobewertung (2005): Hinweise für Reisende in tropische und subtropische Länder zur Vorbeugung lebensmittelbedingter Erkrankungen. Retrieved from https://www.bfr.bund.de/cm/350/hinweisefuerreisendeintropischeundsubtropischelaender.pdf (18.06.2018, 3:35 p.m.).
Center for Disease Control and Prevention: Hymenolepiasis (also known as Hymenolepis nana infection). Retrieved from www.cdc.gov (18th 06. 2018, 3:08 p.m.).
Freie Universität Berlin: Bandwurminfektionen. Retrieved from https://www.kenhub.com/de/library/pathologie/infektionen-durch-bandwuermer (18.06.2018, 2:31 p.m.).
Brehm, Klaus et al. (2013): The genomes of four tapeworm species reveal adaptations to parasitism. Nature 496, S. 57-63, DOI: 10.1038/nature12031.
Robert Koch Institut (2005): Echinokokkose – RKI-Ratgeber. Retrieved from https://www.rki.de/DE/Content/Infekt/EpidBull/Merkblaetter/Ratgeber_Echinokokkose.html (18.06.2018, 16:07).