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Echinococcosis (Hydatid disease)
Updated 9/2001
Distribution:
Most of the world; endemic in South America, North Africa, Middle East, United
States (especially the lower Mississippi Valley and Alaska), North and West
Canada, India, Southern Europe, Australia, and New Zealand - especially in
areas where sheep are raised (Masci, 2001; Goldsmith, 2001).
Agent and Vector:
Echinococcus granulosas, E. multilocularis, and E. vogeli are tapeworms (found
primarily in dogs, but also wolves, foxes, sheep, goats, and camels). The
disease is transmitted through direct contact with infected feces and ingesting
viable parasite eggs with food. Eggs remain viable in the feces of tapeworm
infected canines for weeks allowing transmission to individuals with no direct
contact with the vector animal. Once in the intestine of humans the eggs hatch
to form embryos or oncospheres that penetrate the mucosa and enter the circulation.
Oncospheres then encyst in host viscera and develop in the target organs into
mature larval cysts (King, 2000).
Incubation: Usually
years and can take decades.
Clinical Findings
and Treatment
Signs and Symptoms:
Most people with echinococcus infections are asymptomatic, especially in the
lengthy early stages. Embryos are trapped in various target organs (especially
the liver or lung(s); and also in muscles, bones, kidneys, brain, heart, and
other organs. Embryos that are not destroyed by the body's defenses may develop
into hydatid cyst(s), which grow and eventually cause pain, occlusion, or
dysfunction according to the function or area of the effected organ(s). Most
patients have one such cyst. The hydatid cysts form in the liver in 50-79%
of patients or in the lung 20% and the remaining 10% may be found in the brain,
heart, or the bones. Hepatic cysts may exist as long as 20 years before becoming
large enough to be visible or cause pressure-related problems such as pain,
nausea, cirrhosis, and other manifestations of liver disease. Pulmonary cysts
also may grow for many years before causing dyspnea, cough, or hemoptysis.
Cysts in the brain produce problems consistent with a slow-growing space occupying
lesion (King, 2000; Masci, 2001; Gilman & Lee, 2000).
Complications:
Rupture of cyst or other means of cyst spillage produces infection, occasional
obstruction or allergic reaction in affected organ. In severe cases the allergic
reaction can lead to anaphylactic shock. Rupture releases smaller cysts that
may circulate to other organs. To minimize the risk of releasing circulating
smaller cysts hypertonic saline and ethanol are injected into the large cyst
30 minutes prior to removal. Cardiac and/or pericardial involvement may also
result from the circulating infection. Fortunately, only 10% rupture as the
disease is usually self-limiting (King, 2000).
Diagnosis: Ultrasound
imaging, CT or MRI scan are commonly used. Immunoblot (Western blot) and ELISA
are 80-100% sensitive for liver cysts but only 50-56% for lungs and other
organs. Specificity decreases to 25-56 %. Percutaneous aspiration of cysts
is difficult to perform safely (avoiding cyst spillage). When a cyst ruptures
there is an abrupt stimulation of antibodies. However senescent, calcified,
or dead cysts are seronegative. If the CT shows a cyst regardless of confirmation
by serology the diagnosis should be made (King, 2000; Wilson & Schantz,
2000).
Differential Diagnosis:
Rule out other hepatic cysts and abscesses; other lung disorders such as tuberculosis
or cancer; other cysts, abscesses, or masses in affected organs.
Treatment: Surgical
excision of the cyst remains the treatment of choice for symptomatic cysts
(Safioeas et al, 1999). Albendazole is the drug of choice in treatment as
it is best absorbed. Albendazole is given po at 10-15 mg/kg/day or fixed doses
of 400 mg bid (with meals) in adults cycled for at least three months as follows.
The dosing should be for four weeks followed by a two-week period without
medication. After three months if there is a relapse repeat this dosing regime
for another three months. Mebendazole is more effective on all other types
of worms except tapeworms but can be used as a second drug of choice in higher
doses (50-70 mg/kg/day) dosed tid (with meals) for three months. Praziquantel
is used as adjunct therapy as it only kills the inside of the hydatid cyst
and not the germinal layer. It is currently being used as adjunct therapy
with albendazole for pre and post-operative protection against cyst spillage.
Praziquantel is given in two doses (one dose both pre-operative and post-operative)
of 5-10 mg/kg for both children and adults. Praziquantel causes considerable
nausea and abdominal pain. Patients are appreciative of a dose of promethazine
(Phenergan) prior to praziquantel. Avoid use of praziquantel in pregnancy
or in children less than four years of age. Breast feeding mothers should
not breast feed for 72 hours after treatment is given (Goldsmith, 2001; King,
2000; Moro, 2000; Safioeas et al, 1999).
Prevention: In endemic areas, prevention is primarily via prophylactic treatment of dogs with praziquantel 5mg/kg on a monthly basis to remove the adult tapeworms. Ranchers should be educated to not feed their dogs scrapes from butchered animals. Prolonged freezing of meat (<18 degrees Centigrade) or through cooking of meet (>50 degrees Centigrade) kills cysts in tissue. Careful disposal of human sewage limits the spread of parasitic eggs (King, 2000; Moro, 2000).
Authors: Amy Roberts, FNP & Charles Kemp, FNP - Louise Herrington School of Nursing at Baylor University
References
Goldsmith, R. (2001).
In L.M.Tierney, S.J. McPhee, & M.A. Papadakis (Eds.), Current medical
diagnosis & treatment (40th ed.) (pp.1330-1331). Stamford Connecticut:
Appleton & Lange.
King, C. (2000). Cestodes
(tapeworms). In G. Mandell, J. Bennett, & R. Dolin (Eds.) Principles
and practices of infectious diseases (5th ed.) (pp. 633-640). New York:
Churchill Livingstone.
Masci, J. ( 2001). Echinococcosis.
In F. Ferri (Ed.), Clinical advisor: Instant diagnosis and treatment
(pp.231-232). St. Louis: Mosby.
Moro, P., Gonzales, A., & Gilman, R. (2000). Cystic hydatid disease. In T. Strickland (Ed.), Hunter's tropical medicine and emerging diseases (8th ed.) (pp.866-875). Philadelphia: W.B.Saunders.
Safioeas, M., Misiakos,
E.P., Dosios, T., Manti, C., Lambrou, P., & Skalkeas, G. (1999). Surgical
treatment for lung hydatid disease. World Journal of Surgery, 23, 1181-1185.