Tapeworm Infections

Definition and PathogenesisTop

Tapeworm infections are parasite infections of the gastrointestinal (GI) tract caused by adult forms of various species of cestodes (tapeworms; Taenia spp, Diphyllobothrium spp, and Hymenolepis spp) colonizing the small intestine.

1. Etiologic agent: Most commonly T saginata, less frequently T solium, H nana, and sporadically D latum. T asiatica is limited to Asia and is seen mostly in the Republic of Korea, China, Taiwan, Indonesia, and Thailand. Adult T saginata may be 10 meters long, while the length of T solium is 2 to 3 meters. D latum may be 15 meters long and 0.5 to 2 centimeters wide, while the length of H nana is only 15 to 40 millimeters. Eggs and gravid proglottids are shed with feces and may be ingested by an intermediate host (cattle, pigs). They encyst in the muscles of intermediate hosts and form cysticerci, which are the source of infection in humans.

2. Reservoir and transmission: Humans (definitive hosts) are the reservoir. Infection occurs as a result of consuming raw beef (T saginata), pork (T solium), or fish (trout, pike, perch, salmon, and other freshwater fish species that contain the larvae [D latum]) or ingestion of eggs of H nana (contaminated food, water, hands or accidental swallowing of an infected insect [insect with a cysticercoid larva]).

3. Incubation and contagious period: Eggs appear in stool after 10 to 14 weeks (T solium, T saginata), 3 to 6 weeks (D latum), or 2 weeks (H nana), whereas clinical signs and symptoms develop after several months or years. In the case of T solium and H nana, the patient is contagious throughout the period of egg shedding in feces.

EpidemiologyTop

Tapeworm infections are prevalent worldwide. T saginata is more common in the Middle East, Africa, and South America, while D latum is endemic in Scandinavia, North America, Russia, Eastern Europe, Uganda, and Chile.

Clinical Features and Natural HistoryTop

The infection is usually asymptomatic. It may manifest as mild abdominal pain, nausea, or occasionally as diarrhea. Intestinal obstruction is a rare complication. Cysticercosis (infection caused by larval cysts of T solium) may be a very serious consequence of T solium infection. A frequent presenting sign in T saginata infection is the presence of proglottids on the underwear, as they are motile and crawl out through the host’s anus (proglottids of T solium are discharged passively during defecation). D latum absorbs vitamin B12, which may lead to deficiency presenting as megaloblastic anemia. Patients usually suspect infection when they notice tapeworm segments (proglottids) in their stools.

DiagnosisTop

Diagnosis is based on microscopic identification of tapeworm segments or (occasionally) eggs in stool. Sampling may need to be repeated several times. Eggs of T saginata and T solium are morphologically identical, so the species can only be identified on the basis of microscopic examination of the excreted proglottids.

Differential Diagnosis

Other helminthiases and other causes of abdominal pain (microscopic stool examination is decisive).

TreatmentTop

1. First-line treatment: Oral praziquantel 5 to 10 mg/kg in a single dose; in patients with T solium infection, prior exclusion of clinically silent cysticercosis is necessary, as praziquantel is absorbed from the GI tract and may cause uncontrolled degeneration of cysticerci and brain edema. In H nana infection increase the dose to 25 mg/kg.

2. Second-line treatment: Oral niclosamide (not absorbed from the GI tract) 2 g in a single dose or oral albendazole 400 mg once daily for 3 days (Taenia spp infection); a laxative may be additionally used to facilitate excretion of the parasite.

3. Follow-up: Perform stool sampling for 3 consecutive days to identify the tapeworm species and observe the release of the scolex (the tapeworm’s head). After 1 to 3 months perform microscopic examination of stool to confirm the effectiveness of the therapy.

PreventionTop

Specific Prevention

None.

Nonspecific Prevention

1. Good hand hygiene.

2. Avoiding consumption of raw meat (eg, steak tartare) from unknown sources. Fish and meat should be boiled, roasted, fried, or frozen (≥24 hours at –18 degrees Celsius). Veterinary inspection of cattle and pig farming and slaughter is the key prevention method.