Echinococcosis and Hydatidosis are terms usually applied interchangingly to the zoonotic infections caused by adult and larval stages (metacestodes) of the cestodes belonging to the genus Echinococcous (Family Taenidae).
The term hydatidosis or hydatid disease is restricted with the infection with metacestodes i.e., larval stages only, and where as echinococcosis is applied in a general way, to both adult and larval infections.
The chain of infection that involves dogs and sheep (and also cattle, swine, horses and other herbivorous animals) is the major source of human Echinococcosis.
At present there are four species in the genus Echinococcus, which are valid taxonomically.
Echinococcus spp. requires two mammalian hosts for completion of their life cycles. Eggs are passed in the in the faeces of definitive host, a carnivore. The eggs are highly resistant to environmental conditions and remain infective long periods of time. A wide range of mammals acquires infection by the ingestion of the eggs. Its developmental stage, onchosphere after entering the blood stream are passively transported to the liver, where some are retained. Others reach the lungs and few may be transported further to the kidneys, spleen, muscles, brain, bone or other organs. Here a progressively growing cyst develops, and may contain daughter cysts.
The symptoms in humans are entirely dependent on the location of the cyst. If the cyst is located very superficially swelling may be seen. In many cases the cyst remains latent with out showing any symptoms, for many years. Its presence is by the pressure exerted on the surroundings tissues. Some times the cyst can get infected with bacteria. The cyst may also rupture resulting in severe anaphylaxis, or it may give raise to the development of secondary echinococcosis. Many cysts remain sterile. The animals infested with hydatid cysts may not show any signs and symptoms. The cysts are normally detected during meat inspection or at autopsy. Fertile cysts containing the hexacanth embryo if ingested by meat eating animals develop into Echinococcus worms. Thus the life cycle is completed. In animals having hydatid cyst no clinical symptoms are noticed. However they are usually found during autopsy. Dogs and other canines harboring E granulosus digestive disturbances may be seen in heavily infected animals.
By palpation and percussion clinical diagnosis of Hydatidosis may be made. The affected organ is enlarged in size and a boggy feeling is felt, besides disturbances in its function. Boggy feeling may be differentiated from an abscess. By x-ray, ultrasonography, computerized tomography, Magnetic resonance imaging the hydatid test can be visualized. Several types of blood tests called serological tests are also in vogue. Latex agglutination test, agar gel diffusion test, immunoelectrophorosis, indirect haemagglutination test, Indirect fluorescent antibody test, arc 5 double diffusion test, Enzyme linked immunoassay and intradermal test (Casonis test) are available. Each test has to be validated with clinical condition and correlated carefully. In dogs the stool sample reveals the eggs of E granulosus, on microscopic examination. However the eggs of most of the cestodes the ova have similar morphology and its is not possible to differentiate from other cestodes infections.
Surgical removal of the cyst is the treatment of choice. Albendazole in therapeutic doses for about three months was tried as a treatment of modality and can be tried only in patients who are not fit for surgery. Very recently World Health Organization has suggested a new method called PAIR for the aspiration of cystic hydatidosis. In dogs several anthelmintics are in vogue. Good results are obtained with Praziquantel in 5mg / kg body weight.
Reduction in dog population results in decrease in the prevalence of hydatid disease in man. The dogs are undergoing birth control procedures. And over a period of time it is expected to reduce the dog population. Don't feed slaughterhouse waste to dogs. Keep the dogs away from slaughterhouses. Get the pet dog examined for tapeworm infestation. Get it treated for elimination of the worms. Educate the people about the consequences of dog tapeworm infection.
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