Echinococcus granulosus is a cosmopolitan parasite, and endemic regions exist in each continent. Infection with Echinococcus is often called 'hydatid disease', 'cystic hydatid disease (CHD), or 'hydatosis' because of the hydatic cysts that form. Infection due to E. multilocularis is referred to as alveolar hydatid disease (AHD). This disease is still a substantial cause of death in many parts of the world.
Large public health problems with Echinococcus occur countries of Central America and South America, Western and Southern/Southeastern Europe, the Middle East and North Africa, some sub-Saharan countries, Russia and adjacent countries, and China.
Four species are known pathogens of the disease: E. granulosus, E. multilocularis, E. oligarthrus and E. vogeli. The infection caused by E. granulosus results in cysts in various organs, especially the liver and lungs. These cysts may become quite large and contain hundreds or thousands of scoleces called hydatid sand. Echinococcus granulosas, E. multilocularis, and E. vogeli are tapeworms (found primarily in dogs, but also wolves, foxes, sheep, goats, and camels). Tapeworms have no digestive systems themselves, but absorb nutrients through their skin.
The disease is transmitted through direct contact with infected feces and ingesting viable parasite eggs with food. After ingestion of eggs they hatch releasing tiny hook shaped embryos which penetrate the intestinal mucosa, travel the bloodstream and reach host organs (mainly liver and lung) where they encyst within a week reaching 1 cm in diameter in about 5 months.
Cysts often form in the liver, also in the lungs, as well as in the brain, bones, skeletal muscles, kidney, spleen, and other tissues. A liver cyst may produce no symptoms for 10 to 20 years until it is large enough to be felt by physical examination or to produce symptoms.
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. In severe cases the allergic reaction can lead to anaphylactic shock.
After ingestion of eggs the onchospheres penetrate the intestinal mucosa and reach host organs (mainly liver and lung) where they encyst within a week, reaching 1 cm in diameter in about 5 months. Cysts (2 to 30 cm) are constituted by an external acellular cuticule and an inner cellular "germinal" layer (10-25 µ) that produces the brood capsules containing 6-12 the larvae (scolices) develop from the germinal layer.
Spontaneous or surgical rupture of the cyst can originate a secondary hydatidosis - meaning more cysts. Rupture may cause severe illness, including fever, low blood pressure, and shock. In such cases, the cysts may also disperse and cause widespread disease throughout the body.
Most people with Echinococcus infections are asymptomatic, especially in the lengthy early stages.
abdominal pain in upper right quadrant
severe itching of skin
The degree of antibody response to these cysts will vary depending on their location and degree of calcification. Liver cysts typically produce a higher antibody response than lung cysts. Since Echinococcus eggs are not shed by infected humans, serological determination has been important in the diagnosis of hydatid disease. A number of tests have been used, including latex agglutination (LA), indirect hemagglutination (IHA), complement fixation (CF), agar gel diffusion (AGD) and enzyme linked immunosorbent assay (ELISA).
Cross reactivity between Echinococcosis and Cysticercosiswill occur to some degree in an assay due to the use of crude antigen. It is recommended that any sample showing a positive result by this test be confirmed by additional testing.
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%.
Rule out other hepatic cysts and abscesses; other lung disorders such as tuberculosis or cancer; other cysts, abscesses, or masses in affected organs.
If the cysts are in troublesome locations, the definitive treatment is to remove them surgically if the patient's condition permits the procedure. This can be a complicated type of surgery. 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
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.
Future elimination of this disease will be difficult to attain, requiring decades of sustained effort.
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