Tapeworm infections in humans are caused by fish tapeworm (broad tapeworm, Diphyllobothrium latum and D. nihonkaiense), tapeworm with no hooks (beef tapeworm, Taenia saginata), tapeworm with hooks (pork tapeworm, Taenia solium) and dwarf tapeworm (Hymenolepis nana). A couple of other tapeworms may also parasitize human intestine (Hymenolepis diminuta, Dipylidium caninum).
Distribution
Fish tapeworm is quite common in Scandinavia and in Baltic countries but the prevalence of the disease has decreased over the last few decades. It is also encountered here and there in other parts of Europe and Russia. D. nihonkaiense is found in Chile and in other places around the Pacific.
T. saginata is encountered all over the world. T. solium is rare in muslim countries, but is abundant e.g. in Central America and in parts of Africa.
In addition to the intestinal infestation, T. solium may cause cysticercosis, in which larvae hatching from ingested worm eggs invade the patient's tissues and encapsulate themselves in cysts (see cysticercosis Cysticercosis).
Transmission
Diphyllobothrium infection is contracted by ingestion of larvae-containing raw fish or roe (burbot, pike, perch, ruff; D. nihonkaiense is contracted by eating raw Pacific salmon).
Taenia infection is acquired by eating poorly cooked beef or pork.
Symptoms
Most infestations are asymptomatic. Mild abdominal pain and nausea may occur.
Intestinal obstruction is a very rare complication.
Diphyllobothrium absorbs vitamin B12 from the food taken in by the host, and sometimes the ensuing vitamin deficiency may lead to the development of megaloblastic anaemia Megaloblastic Anaemia with its characteristic symptoms (e.g. smooth tongue, paraesthesias of the limbs, ataxia).
Diagnosis
Diagnosis is based on the identification of eggs from a faecal sample. Worm segments are more rarely found. If one suspects visible segments, full worms or parts of worms, a test to identify the species is used.
Due to sequential release of ova from proglottids, faecal samples on several different days may be necessary for diagnosis.
Eosinophilia may occur in taeniasis but being a non-specific finding it does not help in diagnosis.
Treatment
Diphyllobothrium and T. saginata infections are treated with a single dose of either niclosamide (2 g for adults, 1.5 g for children over 35 kg and 1.0 g for children weighing 11-34 kg) or praziquantel (5-10 mg/kg).
In T. solium infections and in cases where the Taenia species is not known for sure, praziquantel as a single dose of 5-10 mg/kg is preferably used.
Hymenolepis nanainfection is treated with praziquantel (25 mg/kg as a single dose) or with niclosamide(for adults: 2 g once daily for 7 days, for children weighing over 34 kg: 1.5 g on the first day and thereafter 1 g once daily for 6 days, for children weighing 11-34 kg: 1 g on the first day and thereafter 500 mg once daily for 6 days). The treatment is repeated after 10-14 days.
Special local regulations may apply to the prescription of the drugs.
The success of the treatment is controlled after three months by taking new stool samples on three separate days.
Prevention
Fish, roe and meat should be well cooked or frozen (at -18ºC or -0.4F for a minimum of 24 hours). Salting of fish does not destroy Diphyllobothrium larvae.
Meat inspection (Taenia species)
References
Dick TA, Nelson PA, Choudhury A. Diphyllobothriasis: update on human cases, foci, patterns and sources of human infections and future considerations. Southeast Asian J Trop Med Public Health 2001;32 Suppl 2():59-76. [PubMed]
Hoberg EP. Taenia tapeworms: their biology, evolution and socioeconomic significance. Microbes Infect 2002 Jul;4(8):859-66. [PubMed]