Hymenolepsis nana infection (Dwarf tapeworm) is transmitted by dog or cat contact (fecal-oral) or by ingesting infectious agents in food/water. It is usually asymptomatic. Some infected people have diarrhea. It was found in North America in the 1960s among institutionalized children (8% prevalence).
CASES/YEAR
3,000 (US); 62,500,000 (Global)
OTHER NAMES
Dwarf tapeworm (H. nana); Rat tapeworm (Related Infection); Dog tapeworm (Related Infection);
INCUBATION
About 2 weeks for development of mature worms; [CCDM]
INITIAL SYMPTOMS
Usually asymptomatic; Diarrhea, abdominal pain, weight loss, and fatigue may result from dwarf tapeworm infection. [CCDM]
PRECAUTIONS
"The infection is communicable for as long as eggs are passed in feces and may persist for years." [CCDM, p. 601]
COMMENTS
Probably the most common tapeworm; Up to 26% prevalence in some areas; Up to 8% prevalence among institutionalized in US; [PPID, p. 3465-6] The dwarf tapeworm is the only tapeworm transmitted person to person by the fecal-oral route or by autoinfection. Contaminated food and water are also sources of infection. Mice may be reservoirs for dwarf tapeworms. Insects that carry the larvae include mealworms, flea larvae, beetles, and cockroaches. [CCDM, p. 601-2] Hymenolepiasis may be associated with eosinophilia and skin eruptions. [Guerrant, p. 942] Dwarf tapeworm autoinfection can result in a massive number of worms in the gut with resulting nausea/vomiting, diarrhea, abdominal pain, and weight loss. [Merck Manual, p. 1533]
RELATED INFECTIONS:
Like the dwarf tapeworm, the rat tapeworm (Hymenolepsis diminuta) and dog tapeworm (Dipylidium caninum) may infect humans who ingest insects containing the larvae. Humans are accidental hosts for rat and dog tapeworms. The dog tapeworm (dipylidiasis) infects both dogs and cats. Human infections are unusual. Parents may find tapeworm segments in toddler's stool. Infection of children can be prevented by keeping pets free of fleas and worms. [CCDM, p. 602]
DIAGNOSTIC
Microscopic exam for ova in feces; Proglottids of the dog tapeworm (Related Infection) appear in the stool and look like moving cucumber seeds. [PPID, p. 3466-7]
SCOPE
Global; Endemic foci in Asia, southern & eastern Europe, Central & South America, and Africa; [PPID, p. 3465]
SIGNS & SYMPTOMS
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>fatigue, weakness
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G abdominal pain
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G diarrhea
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G nausea, vomiting
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H eosinophilia
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*weight loss
SOURCE
Person-to-Person, Human Fecal-Oral, Animal Excreta, Eating Contaminated Food, Waterborne (Ingesting, Inhaling, or Swimming)
RESERVOIR
Cats, Dogs, Rodents, Human
RISK FACTORS
- Have dog or cat contact (fecal-oral)
- Ingest infectious agents in food/water
REFERENCES FOR CASES/YEAR
1. (US) Dwarf tapeworm was found In North America in past (1960s) among institutionalized children (8% prevalence); [PPID, p. 3465] 1/20 of global cases/yr = 60 million/20 = 3 million; Guesstimate: 1/1000 of global rate = 3 million/1000;
2. (Global) Infection is common in institutionalized children; [Harrison ID, p. 1158] Estimated 50 to 75 million people infected; Dipylidium caninum infection is common in dogs and cats, but unusual in humans. [Cecil, p. 2117-8]