ABSTRACT
A single case of severe hydatidosis in a liver of a Najdi sheep was studied. The estimated age of the animal was 1.5 years and the liver was infected with 29 cysts and their diameters ranged from 4.0 mm to 5.1 cm. Cysts with a diameter less than 10 mm were immature and those of more than 1.5 cm were fertile and developed protroscoleces. Harvested protroscoleces measured 120 x 60 to 140 x 80 um. Comparative histochemical studies by hematoxylin and eosin, periodic acid Schiff [PAS] and Masson's trichrome stains revealed that the cystic wall consisted of three layers [germinal, laminated and fibrous, respectively]. The thickness varied with each stain. The glycogen and mucopolysaccharide content increased in the infected sheep. Histopathological changes were the formation of fibrotic capsules around biliary tracts and portal vein and also leaky liver was marked in all the sections examined. Meanwhile, pre-malignant changes were seen in the different foci, particularly around the biliary tracts and portal veins. The histochemical structure of the hydatid cyst wall may pave the way for an effective therapeutic treatment