Tapeworm
Tapeworm: Excerpt from The 5-Minute Pediatric Consult
Jessica S. Hart, MDSamir S. Shah, MD, MSCE
Tapeworm - BASICS
Tapeworm - description
- Tapeworms cause 2 major types of zoonotic disease syndromes, depending on whether humans are the definitive or intermediate host. When humans serve as definitive hosts, adult tapeworms infect the GI tract and interfere with nutrition. These infections are often asymptomatic. When humans serve as intermediate hosts for the larval cestode, serious pathology results.
- Causative organisms include:
- Taenia saginata (beef tapeworm)
- Taenia solium (pork tapeworm)
- Diphyllobothrium latum (fish tapeworm)
- Dipylidium caninum (dog tapeworm)
- Echinococcus granulosus
Tapeworm - general prevention
- Adult tapeworms:
- Proper cooking of meat and fish prevents transmission of beef, pork, and fish tapeworms.
- Pork tapeworm:
- The refrigeration of pork infested with cysticerci at temperatures >0°C (32°F) does not affect parasite survival. However, storage of pork for 4 days at −5°C (21.2°F) or 1 day at −24°C (−11.2°F) kills most cysticerci.
- Fish tapeworm:
- Brief cooking (at 56°C [132.8°F] or higher for 5 minutes) or freezing (−18°C [−0.4°F] for 24 hours) renders the fish safe for consumption.
- Dog tapeworm:
- Periodic deworming of pets prevents infections.
- Echinococcosis:
- Careful disposal of sheep viscera and mass chemotherapy of dogs can interrupt the life cycle of E. granulosus as the cestode moves between sheep and carnivore hosts.
Tapeworm - epidemiology
- Beef tapeworm:
- Widespread in cattle-breeding areas of the world, with a prevalence of >10% in areas of Africa, such as Ethiopia and Kenya, and the former Soviet Union
- Pork tapeworm:
- Cysticercosis has a high prevalence in developing areas of Central and South America.
- In the US, immigrants account for >90% of cases.
- Fish tapeworm:
- Infection is most prevalent in temperate climates of Europe, North America, and Asia. Persons who prepare raw fish are most at risk.
- In the US, infected salmon have been implicated in most cases.
- Dog tapeworm:
- Found in dogs and cats worldwide.
- Echinococcosis:
- Associated with the practice of feeding sheep viscera to dogs
- It is hyperendemic in sheep-raising areas of South America, Australia, areas of Africa, China, central Asia, and the western US
Tapeworm - pathophysiology
- Beef tapeworm:
- Cattle (intermediate host) ingest the eggs of T. saginata in contaminated feeds. The eggs hatch, releasing embryos. The embryos penetrate the intestinal mucosa, enter the bloodstream, and settle in various tissues, where they develop into larvae. Larvae in undercooked meat are consumed by humans and mature into adult tapeworms within the human (definitive host) GI tract. They grow up to 25 m in length.
- Pork tapeworm: Humans are the only definitive host for the adult pork tapeworm, whereas both humans and pigs are intermediate hosts for its embryonic form, cysticercus.
- Pigs (intermediate host) ingest T. solium eggs. In the intestine, the eggs release embryos that penetrate the mucosa, enter the bloodstream, and settle in various tissues to differentiate into cysticerci (infective larvae). Cysticerci are ingested by humans (definitive host) who consume undercooked pork.
- Humans (intermediate host) ingest food contaminated with human feces containing T. solium eggs. The eggs hatch, liberating embryos (oncospheres). Penetration through the intestinal mucosa leads to blood-borne distribution to the brain, subcutaneous tissues, muscle, and eye, where they develop into cysticerci.
- Fish tapeworm:
- When sewage containing D. latum eggs contaminates freshwater lakes and streams, larvae hatch into the water. These larvae are eaten by crustaceans and fish. Humans are infected when they consume these undercooked fish. The larvae mature into adult tapeworms in the intestines of humans.
- Dog tapeworm:
- Larvae develop in fleas (intermediate host) after ingestion of the eggs; humans infected through accidental ingestion of infected fleas.
- Echinococcosis (hydatid disease):
- Humans ingest eggs of E. granulosus through contaminated dog feces. After ingestion, the eggs hatch and release embryos (oncospheres) in the small intestine. Penetration through the mucosa leads to blood-borne distribution to the liver, lungs, and other sites, where development of cysts begins. Within the cysts, new larvae (scolices) develop, accumulate fluid, and encroach on surrounding structures.
Tapeworm - DIAGNOSIS
Tapeworm - signs & symptoms
- Recent travel or immigration:
- Tapeworm infections are more prevalent in other countries.
- GI tract:
- Nausea, weight loss, diarrhea, abdominal tenderness or distention
- Fish tapeworm and, rarely, dog tapeworm infections can be complicated by intestinal obstruction.
- May observe proglottids that resemble rice or seeds in stool from dog tapeworm infections
- Jaundice:
- Hepatic cysts from echinococcosis may be palpable in the right upper quadrant.
- Biliary tree extension can lead to obstructive jaundice and cholangitis.
- Respiratory tract:
- Pulmonary hydatid cyst due to E. granulosus causes cough, dyspnea, and hemoptysis; rupture of a cyst can cause anaphylaxis
- Hematologic:
- Signs of anemia secondary to vitamin B
- CNS:
- New-onset seizures (partial or generalized) are a typical manifestation of neurocysticercosis and some species of Echinococcus.
- Neurocysticercosis may present with alteration in mental status, signs of elevated intracranial pressure (headache, vomiting, visual changes) or meningitis
- Both neurocysticercosis and vitamin BCNS symptoms in neurocysticercosis typically appear 5−7 years after initial infection (range, 6 months to 30 years).
- Note: For echinococcosis, there is usually a presymptomatic stage that may last for years before the enlarging cysts cause symptoms. The variability of signs and symptoms depend on the target organ.
Tapeworm - tests
Tapeworm - lab
- Beef tapeworm:
- Identification of scolex in stool
- Ziehl-Neelsen stain of stool or perianal adhesive tape preparations identifies eggs.
- Collection of proglottids in saline with microscopic examination
- ELISA test detects Taenia antigens in stool.
- Pork tapeworm:
- ELISA test and immunoblot in combination for parenchymal cysticercosis
- Stool samples for intestinal worms as for beef tapeworm
- Fish tapeworm:
- Stool samples for eggs and proglottids are diagnostic.
- Mild eosinophilia (5–15%) may be present.
- 50% of patients have low vitamin B2% have megaloblastic anemia.
- Dog tapeworm
- Characteristic egg packets (loose membrane containing up to 20 eggs) may be identified in stool or perianal adhesive tape preparations.
- Echinococcosis:
- IgE levels are elevated. Eosinophilia is present in <25% of infected persons.
- Mild elevation of hepatic enzymes may be present with hepatic hydatid cysts.
- The Casoni skin test (injection of hydatid fluid into the dermis) yields an erythematous papule in <60 minutes in 50–80% of infected patients. There is a false-positive result in 30% of uninfected patients.
- Serologic testing is falsely negative in 10–50% of cases. False-negative results are more likely in patients with pulmonary hydatid cysts and in children. No current serologic test excludes the diagnosis of hydatid cysts.
Tapeworm - imaging
Pork tapeworm:
- Contrast-enhanced CT or MRI of the brain may reveal cysticerci; surrounding edema represents a dying parasite, calcification represents a resolved infection.
- Soft tissue x-ray may show calcifications of inactive cysts
- Imaging is usually diagnostic Echinococcosis
- On x-ray, pulmonary cysts demonstrate a sharply demarcated, smooth-bordered cyst; there is a crescent-shaped air level after cyst rupture. Liver and spleen lesions may calcify, but only over many years.
- Demonstration of internal septa or daughter cysts (after cyst rupture) by CT, MRI, or ultrasound indicates hydatid cysts. May be present in ~50% of patients with unilocular liver cysts.
Tapeworm - diag proced-surgery
Echinococcosis:
- In seronegative persons, a presumptive diagnosis can be confirmed by demonstrating protoscolices or hydatid membranes in the liquid obtained from percutaneous aspiration of the cyst under ultrasound guidance. This procedure is controversial because of risk of anaphylaxis if rupture occurs.
Tapeworm - differencial diagnosis
- Nontapeworm gastroenteritis
- Irritable bowel syndrome/Inflammatory bowel disease
- Cholecystitis or biliary obstruction (i.e., gallstones, neoplasms, or liver disease)
- BIdiopathic epilepsy
- Echinococcal cysts must be differentiated from benign cysts, cavitary tuberculosis, abscesses, and neoplasms.
Tapeworm - TREATMENT
Tapeworm - medication
Tapeworm - first line
