CESTODES
CESTODESCestodes, or tapeworms, are segmented worms. The adults reside in the Gastrointestinal tract, but the larvae can be found in almost any organ. two major clinical groups. Humans are the definitive hosts, with the adult tapeworms living in the gastrointestinal tract (Taenia saginata, Diphyllobothrium, Hymenolepis, and Dipylidium caninum). Humans are intermediate hosts, with larval-stage parasites present in the tissues; diseases in this category include echinococcosis, sparganosis, and coenurosis. Taenia solium, the human may be either the definitive or the intermediate host.
The ribbon-shaped tapeworm attaches to the intestinal mucosa by means of sucking cups or hooks located on the scolex. Proglottids (segments) form behind the scolex and constitute the bulk of the tapeworm The length varies among species. In some, the tapeworm may consist of more than 1000 proglottids and may be several meters long. The mature proglottids are hermaphroditic and produce eggs, which are subsequently released.
Since eggs of the different Taenia species are morphologically identical, differences in the morphology of the scolex or proglottids provide the basis for diagnostic identification to the species level. Most human tapeworms require at least one intermediate host for complete larval development.
Taeniasis Saginata Etiology and Pathogenesis: Humans are the definitive host for Taenia saginata, the beef tapeworm, which inhabits the upper jejunum. Eggs are excreted in feces and ingested by cattle or other herbivores; larvae encyst (cysticerci) in the striated muscles of these animals. When humans ingest raw or undercooked beef, the cysticerci mature into adult worms.
Clinical Features: Pts may experience perianal discomfort, mild abdominal pain, nausea, change in appetite, weakness, and weight loss.
Diagnosis: The diagnosis is made by detection of eggs or proglottids in the stool. Eggs may be found in the perianal area. Eosinophilia may develop, and IgE levels may be elevated.
TREATMENT: Praziquantel is given in a single dose of10 mg/kg.
Taeniasis Solium and Cysticercosis Etiology and Pathogenesis: Humans are the definitive host and pigs the intermediate host for T. solium, the pork tapeworm. The disease, which is due to ingestion of pork infected with cysticerci, is similar to taeniasis saginata.
If humans ingest T. solium eggs (e.g., as a result ofclose contact with a tapeworm carrier or via autoinfection), they develop cysticercosis. Larvae penetrate the intestinal wall and are carried to many tissues, where cystercerci develop.
Clinical Features:• Intestinal infections: Epigastric discomfort, nausea, a sensation of hunger, weight loss, and diarrhea can occur, but most infections are asymptomatic.
• Cysticercosis: Cysticerci can be found anywhere in the body but most often are detected in the brain, skeletal muscle, SC tissue, or eye. Neurologic manifestations are most common and include seizures due to inflammation surrounding cysticerci in the brain, hydrocephalus (from obstruction of CSF flow by cysticerci and accompanying inflammation or by arachnoiditis), headache, nausea, vomiting, changes in vision, dizziness, ataxia, and confusion.
Diagnosis: Intestinal infection is diagnosed by detection of eggs or proglottids in stool. Calcified cysts in muscles can be recognised radiologically. In the brain, however, less calcification takes place and larvae are only occasionally visible by plain X-ray; usually CT or MRI will show them.
Epileptic fits starting in adult life suggest the possibility of cysticercosis if the patient has lived in or travelled to an endemic area. The subcutaneous tissue should be palpated and any nodule excised for histology. Radiological examination of the skeletal muscles may be helpful. Antibody detection is available for serodiagnosis
TREATMENT:Intestinal infections respond to a single dose of praziquantel (10 mg/kg). Neurocysticercosis can be treated with albendazole (15 mg/kg per day for 8–28 days) or praziquantel (50–60 mg/kg daily in 3 divided doses for 15 days or 100 mg/kg in 3 doses given over 1 day).
Patients should be carefully monitored, given the potential for an inflammatory response to treatment. High-dose glucocorticoids can be administered during treatment, particularly if symptoms become worse during therapy; since glucocorticoids induce praziquantel metabolism, cimetidine should be given with praziquantel to inhibit this effect.
Supportive measures include antiepileptic administration and treatment of hydrocephalus as indicated
Echinococcosis Etiology and Pathogenesis: Echinococcosis is an infection of humans that is caused by Echinococcus larvae. The adult worm of E. granulosus lives in the jejunum of dogs and releases eggs that humans may ingest.
Disease is prevalent in areas where livestock is raised in association with dogs. After ingestion, embryos escape from the eggs, penetrate the intestinal mucosa, enter the portal circulation, and are carried to many organs but particularly the liver and lungs.
. Larvae develop into fluid-filled unilocular hydatid cysts within which daughter cysts develop, as do germinating cystic structures. Cysts expand over years. E. multilocularis, found in arctic or subarctic regions, is similar, but rodents are the intermediate hosts. The parasite is multilocular, and vesicles progressively invade host tissue by peripheral extension of processes from the germinal layer.
Clinical Features: Expanding cysts exert the effects of space-occupying lesions, causing symptoms in the affected organ. Pts with hepatic disease most commonly present with abdominal pain or a palpable mass in the RUQ. Compression of a bile duct may cause biliary obstruction or may mimic cholelithiasis.
Rupture or leakage from a hydatid cyst may cause fever, pruritus, urticaria, eosinophilia, or anaphylaxis. Pulmonary cysts may rupture into the bronchial tree or the peritoneal cavity and cause cough, chest pain, or hemoptysis. Rupture of cysts may result in multifocal dissemination. E. multilocularis disease may present as a hepatic tumor, with destruction of the liver and extension into vital structures.
Daughter cysts removed at surgery
Diagnosis: Radiographic imaging is important in evaluating echinococcal cysts. Daughter cysts within a larger cyst are pathognomonic. Eggshell or mural calcification on CT is indicative of E. granulosus infections. Serology may be useful but can be negative in up to half of pts with lung cysts.Diagnosis: Serology is usually positive in patients with hepatic disease. Aspiration of cysts usually is not attempted because leakage of cyst fluid can cause dissemination or anaphylactic reactions.
TREATMENT: Ultrasound staging is recommended for E. granulosus infection. Therapy is based on considerations of the size, location, and manifestations of cysts and the overall health of the pt. For some uncomplicated lesions, percutaneous aspiration, infusion of scolicidal agents, and re-aspiration are recommended.
TREATMENT: Albendazole (15 mg/kg daily in 2 divided doses for 4 days before the procedure and for at least 4 weeks afterward) is given for prophylaxis of secondary peritoneal echinococcosis due to inadvertent spillage of fluid during this treatment. Surgery is the treatment of choice for complicated E. granulosus cysts.
TREATMENT: Albendazole should also be given prophylactically, as just described. Praziquantel (50 mg/kg daily for 2 weeks) may hasten the death of protoscolices.
TREATMENT: Medical therapy alone with albendazole for 12 weeks to 6 months results in cure in _30% of cases and in clinical improvement in another 50%. E. multilocularis infection is treated surgically, and albendazole is given for at least 2 years after presumptively curative surgery. If surgery is not curative, albendazole should be continued indefinitely.
Diphyllobothriasis Diphyllobothrium latum, the longest tapeworm (up to 25 cm), attaches to the ileal and occasionally the jejunal mucosa. Humans are infected by eating raw fish. Symptoms are rare and usually mild, but infection can cause vitamin B12 deficiency because the tapeworm absorbs large amounts of vitamin B12 and interferes with ileal B12 absorption
Diphyllobothriasis Up to 2% of infected pts, especially the elderly, have megaloblastic anemia resembling pernicious anemia and can suffer neurologic sequelae due to B12 deficiency. The diagnosis is made by detection of eggs in the stool. Praziquantel (5–10 mg/kg once) is highly effective.