Cestodes - Parasitic Infections - AntiinfectiveMeds.com

Human infections caused by cestodes, or tapeworms, may occur within the lumen of the bowel, where adult cestodes attach themselves to the host intestine (Box 1). Alternatively, human infection may be the result of dissemination of cestodes from the bowel to involve extraintestinal sites, often by larval forms of the parasite. The life cycle of cestodes is determined by definitive hosts, in whom the mature adult worm lives, and intermediate hosts, which harbor the larval forms of the parasite.

Humans are a definitive host for six cestodes: Diphyllobothrium latum, Taenia solium, Taenia saginata, Hymenolepis diminuta, Hymenolepis nana, and Dipylidium caninum. In addition, humans may be intermediate hosts for Echinococcus granulosis and Echinococcus multilocularis. All forms of disease associated with infections caused by cestodes are treatable; therefore, a careful history and physical examination to identify potential patients is warranted.

Cestodes attach themselves to the intestinal mucosa by means of a specialized organ called the scolex, which has a distinctive morphology for each species of cestode. Attached to the scolex are one to several hundred segments called proglottids. Proglottids each contain both male and female reproductive organs and may be classified as immature, mature, or gravid, based on the state of maturation of their sex organs. A gravid proglottid contains a fully developed uterus, full of eggs. The uterine structure of a gravid proglottid helps to differentiate species of cestode.

Diphyllobothrium Latum Infection

Taenia Solium Infection

Cysticercosis (Cysticercus Cellulosea Infection)

Taenia Saginata Infection

HYMENOLEPIS NANA INFECTION

Essentials of Diagnosis

Adult worms and proglottids are rare.
Spheroidal and thin-walled eggs (30-47 mm).
Eggs contain two polar elements from which 4-8 filaments project (diagnostic).
Scolex has hooklets and four suckers.

General Considerations

H nana is distributed worldwide and is called the dwarf tapeworm because of its small size (2-4 cm). Endemic areas include Asia, Africa, South and Central America, and southern and eastern Europe. Infection with H nana is acquired by the ingestion of eggs, commonly from human stool. The eggs hatch within the stomach or small intestine, and the resultant larvae attach to the bowel wall, where adult worms develop in several weeks. Eggs are released directly from the gravid proglottids while these proglottids are still attached to the adult worm; therefore proglottids are rarely seen on stool examination. Various arthropods such as fleas can serve as alternate intermediate hosts for H nana. Eggs produced within infected humans can lead to internal autoinfection, and poor fecal-oral hygiene can cause infection to be passed from one person to another.

Clinical Findings

Signs and Symptoms

Infection with H nana is most often asymptomatic, yet some patients may complain of headache, dizziness, anorexia, or abdominal pain. Whether these symptoms are related to the infection is uncertain. Children may have headache or sleep and behavioral disturbances, which resolve after successful treatment of the infection.

Laboratory Findings

As for patients with other cestode infections, examination of blood from patients with H nana infection is typically normal, although a mild leukocytosis with eosinophilia may be present. Microscopic stool examination will frequently reveal eggs, but finding proglottids is uncommon with H nana infection.

Differential Diagnosis

Since infection with H nana is usually asymptomatic, patients most often discover H nana infection as an incidental finding on stool examination done for another reason. In patients with nonspecific gastrointestinal complaints, peptic ulcer disease and malignancy need to be ruled out. Similarly, in children with behavioral symptoms, a variety of neurologic disorders of organic and psychologic origins need to be considered.

Complications

Through a mechanism that is still unclear, seizures have been reported with H nana infections.

Treatment

Cysts of H nana are more resistant to therapy than adult worms. Therefore higher doses or longer courses of therapy are required to eradicate cysts than with other cestode infections. Therapy for infection by H nana consists of a single dose of either praziquantel or niclosamide (see Box 2). Follow-up examinations of stool should be performed at 2 weeks and 3 months after therapy.

Prognosis

Since infection with H nana is usually asymptomatic and infection responds to therapy, the prognosis is excellent.

Prevention & Control

Infection with H nana can be prevented with good fecal-oral hygiene and adherence to the principles of sanitation (eg, appropriate disposal of human sewage) (Box 3). Incidental ingestion of arthropod hosts may also produce infection, although this mechanism of infection is uncommon.

HYMENOLEPIS DIMINUTA

Essentials of Diagnosis

Proglottids are rare in stool, but adult worms may be present.
Ovoid and thick-walled eggs (70-85 um by 60-80um).
Eggs contain no polar elements.
Scolex has no hooklets and four suckers.

General Considerations

H diminuta is also distributed worldwide, but the incidence of infection is much less common than with H nana. Infection with H diminuta is acquired by the ingestion of eggs, produced from an obligatory arthropod intermediate host. The eggs hatch within the stomach or small intestine, and the adult worms develop in several weeks. Eggs are similar in size to the eggs of H nana but may be distinguished by their lack of polar filaments and ovoid shape. In contrast to H nana, the life cycle of H diminuta requires an intermediate arthropod host, and adult worms may be passed in the stool of humans.

Clinical Findings

Signs and Symptoms

Infection with H diminuta is not associated with clinical symptoms.

Laboratory Findings

Microscopic stool examination will frequently reveal eggs and adult worms. Blood examination may demonstrate mild leukocytosis with eosinophilia.

Differential Diagnosis

The finding of H diminuta in human infection is commonly an incidental finding that is asymptomatic.

Complications

No complications have been reported.

Treatment

Therapy for infection for H diminuta consists of niclosamide in a one-time dose (see Box 87-2).

Prognosis

H diminuta responds promptly to therapy, so the prognosis is excellent.

Prevention & Control

Infection with H diminuta can be reduced by decreasing exposure to arthropod vectors, such as by rat control measures (Box 3).

Dipylidium Caninum Infection

Echinococcal Infection

BOX 1.

Syndrome	More Common	Less Common
Diphyllobothrium latum infection	Bloating, abdominal pain, diarrhea	Intestinal obstruction, vitamin B₁₂deficiency
Taenia solium infection	Asymptomatic	Indigestion, nausea
Cysticercosis (extraintestinal T solium infection)	Headache, seizures, neurologic deficits	Myositis, liver or heart failure
Taenia saginata infection	Asymptomatic	Abdominal cramps, malaise
Hymenolepis nana infection	Abdominal pain	Dizziness, anorexia; children-behavioral disturbance
Hymenolepis diminuata infection	Asymptomatic
Dypylidium caninum infection	Asymptomatic	Indigestion, anorexia, anal pruritis
Echinococcal infection	Abdominal pain, mass	Seizures, headache, neurologic deficits, bone pain

BOX 2.

Syndrome	Adult treatment	Pediatric treatment
Diphyllobothrium latum infection	Praziquantel, 10–20 mg/kg once OR Niclosamide 2 g once	Praziquantel, 10–20 mg/kg once OR Niclosamide (11–34 kg), 1 g once; (>34 kg), 1.5 g once
Taenia solium infection	Praziquantel, 10–20 mg/kg once OR Niclosamide, 2 g once	Praziquantel, 10–20 mg/kg once OR Niclosamide (11–34 kg), 1 g once; (>34 kg), 1.5 g once
Cysticercosis (extraintestinal T solium infection)	Surgery and either Praziquantel, 20 mg/kg three times daily × 15–30 d OR Albendazole, 7.5 mg/kg three times daily × 8 d	Surgery and either Praziquantel, 20 mg/kg three times daily × 15–30 d OR Albendazole, 7.5 mg/kg three times daily × 8 d
Taenia saginata infection	Praziquantel, 10–20 mg/kg once OR Niclosamide, 2 g once	Praziquantel, 10–20 mg/kg once OR Niclosamide (11–34 kg), 1 gm once; (>34 kg), 1.5 g once
Hymenolepis nana infection	Praziquantel, 10–20 mg/kg once OR Niclosamide, 2 g once	Praziquantel, 10–20 mg/kg once OR Niclosamide (11–34 kg), 1 gm once; (>34 kg), 1.5 g once
Hymenolepis diminuta infection	Niclosamide, 2 g once	Niclosamide (11–34 kg), 1 g once; (>34 kg), 1.5 g once
Dypylidium caninum infection	Niclosamide, 2 g once	Niclosamide (11–34 kg), 1 g once; (>34 kg), 1.5 g once
Echinococal infection	Surgery and albendazole, 400 mg divided into 2 daily doses × 3 mo OR Mebendazole, 50 mg/kg/d divided into 3 daily doses × 3 mo	Surgery and albendazole, 15 mg/kg/d divided into 2 daily doses × 3 mo OR Mebendazole, 50 mg/kg/d divided into 3 daily doses × 3 mo

BOX 3.

Syndrome	Preventative Measures
Diphyllobothrium latum infection	Adequate cooking of fish or freezing fish for 48 h
Taenia solium infection	Adequate cooking of pork or pork products
Cysticercosis (extraintestinal T solium infection)	As for T solium
Taenia saginata infection	Adequate cooking of beef and beef products; inspection of beef and destruction of infected carcasses
Hymenolepis nana infection	Adherence to good fecal–oral hygiene
Hymenolepis diminuta infection	Arthropod control measures (such as rat control)
Dypylidium caninum infection	Screening of dogs and cats; treatment of infected animals
Echinococcal infection	Screening of household pets; treatment of infected animals Destruction of infected carcasses Education on routes of transmission (in endemic areas)