Echinococcosis(redirected from hydatid cyst)
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a helminthic disease of humans and animals caused by parasitic larvae of the tapeworm Echinococcus. Humans become infected by swallowing the eggs of the helminths, mostly after touching dogs. Larvae emerge from the eggs in the intestine, penetrate into the blood vessels, and are carried to various organs, where they change into hybrid cysts.
Two forms of echinococcosis are distinguished: hydatid disease and alveococcosis. Hydatid disease, the commoner of the two, is caused by the parasite E. granulosus, which mainly affects the liver, lungs, brain, muscles, and kidneys. It is unilocular and grows slowly over a period of years. The cyst sometimes has a volume of 10 1 or more. A connective-tissue capsule and chitinous membrane form around it while daughter hydatids form in the lumen of the cyst and sometimes produce granddaughter hydatids.
The alveolar or multilocular form of echinococcosis is less common. The causative agent of alveococcosis is E. (Alveococcus) multilocularis. It infests the liver almost exclusively. The alveolar echinococcus is a conglomerate of small cysts, called the parasitic node. Its rapid infiltrating process of growth is similar to that of a malignant tumor.
Echinococcosis usually interferes with the functions of the affected organ and causes it to atrophy. The contents of the cyst are allergenic and toxic, causing periodic outbreaks of hives and eo-sinophilia.
The symptoms of echinococcosis vary, depending on the location of the tapeworm. If the liver is involved, pain is felt in the upper right side of the abdomen; the liver enlarges, and jaundice sometimes occurs as a result of compression of the major bile ducts. Echinococcosis of the lungs is accompanied by chest pains and coughing. Sometimes the membrane and hooks of the parasites and hydatid fluid are discharged with sputum. Alveococcosis is characterized by extreme density of the liver and spread of the parasite to adjacent organs.
A diagnosis of echinococcosis is based on the results of clinical examinations, X rays, epidemiology, serodiagnosis, and Casoni’s intradermal test, which involves the injection of hydatid fluid into the skin. Treatment is mainly surgical, including the extirpation or lancing of a cyst and removal of a chitinous cyst with its contents, or the removal of the affected organ. Alveococcosis requires liver resection or enucleation of the parasitic node.
Echinococcosis of animals is caused by E. granulosus larvae that infest various internal organs of the intermediate hosts, which include many species of farm animals. The adult parasites, in the tapeworm stage, inhabit the small intestine of the definitive hosts, carnivorous animals.
Echinococcosis is common throughout the world. Dogs, which excrete the parasite’s eggs into the environment, are the main source of the causative agent. Sheep, cattle, swine, reindeer, and, less commonly, camels, goats, and horses are susceptible to the disease, which develops after the animals swallow the parasite’s eggs with feed or water. As the cysts grow, they compress the surrounding tissues, cause them to atrophy, and impair the functioning of organs, resulting in digestive and respiratory disorders, for example. The metabolites excreted by the parasites poison the animals.
Echinococcosis has no typical symptoms, because these vary with the location of the cysts and the severity of infestation. They may include dyspnea, coughing, exhaustion, and decrease in work productivity. The diagnosis is based on the results of immunity tests. No treatment is as yet available. Prevention consists in veterinary inspection of the slaughter of cattle and the detection and destruction of affected organs. It is imperative not to allow dogs to feed on the bodies of dead animals. Working dogs, especially those used in cattle-raising regions, should be periodically checked and dewormed and be taken care of properly.
REFERENCESDeineka, I. Ia. Ekhinokokkoz cheloveka. Moscow, 1968.
Lukashenko, N. P., and I. L. Bregadze. “Ekhinokokkoz i al’veokokkoz.” In Mnogotomnoe rukovodstvo po mikrobiologii, klinike i epidemiologii infekts’tonnykh boleznei, vol. 9. Moscow, 1968. Pages 509–26.
A. G. KISSIN