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Hydatidosis

Cystic hydatidosis/echinococcosis is an important zoonosis caused by the tapeworm Echinococcus granulosus. At present, four species of Echinococcus are recognized: E. granulosus, E. multilocularis, E. oligarthrus and E. vogeli. The parasite is distributed worldwide and about 2–3 million patients are estimated in the world (40). It causes serious human suffering and considerable losses in agricultural and human productivity. General lack of awareness of transmission factors and prevention measures among the population at risk, abundance of stray dogs, poor meat inspection in abattoirs, improper disposal of offal and home slaughtering practices play a role in the persistence of the disease. The incidence of surgical cases ranges from 0.1 to 45 cases per 100 000 people. The real prevalence ranges between 0.22% and 24% in endemic areas. Ultrasounds have been very useful in large-scale prevalence surveys. Large prevalence studies have been conducted in many countries: in the Libyan Arab Jamahiriya, Morocco and Tunisia, the prevalence ranged from 1% to 2%.

In the normal life-cycle of Echinococcus species, adult tapeworms (3–6 mm long) inhabit the small intestine of carnivorous defi nitive hosts, such as dogs, coyotes or wolves, and echinococcal cyst stages occur in herbivorous intermediate hosts, such as sheep, cattle and goats. In most infected countries there is a dog–sheep cycle in which grazing sheep ingest tapeworm eggs passed in the faeces of an infected dog. Dogs ingest infected sheep viscera, mainly liver and lungs, containing larval hydatid cysts in which numerous tapeworm heads are produced. These attach to the dog’s intestinal lining and develop into mature adult tapeworms. Humans become infected by ingesting food or drink contaminated with faecal material containing tapeworm eggs passed from infected carnivores, or when they handle or pet infected dogs. Oncospheres released from

the eggs penetrate the intestinal mucosa and lodge in the liver, lungs, muscle, brain and other organs, where the hydatid cysts form. In the CNS, hydatidosis produces spinal disease and also is a potential cause of intracranial hypertension. To control the parasite, a number of antihelminthic drugs have proved to be effective against adult stages of E. granulosus in the fi nal host. The best drug currently available is praziquantel which exterminates all juvenile and adult echinococci from dogs. Several of the benzimidazole compounds have been shown to have effi cacy against the hydatid cyst in the intermediate host. Echinococcosis can be controlled through preventive measures that break the cycle between the defi nitive and the intermediate host. These measures include dosing dogs, inspecting meat and educating the public on the risk to humans and the necessity to avoid feeding offal to dogs.

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