الفهرس 
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Abstract
Two hundred and twenty four mice (4 to 6 wk old) were divided into 7 equal groups (gps 1 to 7) to study the appropriate dose of ETV causing minimal tissue damage. Gp. (1) served as untreated control. Gps (2, 3 and 4) served as experimental control groups where mice were infested orally with a single dose of either 200, 500 or 1000 embryonated ETV, respectively. Gps (5, 6 and 7) served as experimental groups where mice were infested orally with triple doses of either 200, 500 or 1000 embryonated ETV, with 10 day intervals, respectively. The schedule of necropsy was 12 and 24 hr PI, besides 4, 7, 10, 20, 30 and 60 day PI. Specimens were collected from the liver, lungs, kidneys, small and large intestines, heart, spleen, brain and skeletal muscles. Specimens were fixed in 10% neutral buffered formalin, processed and examined histopathologically. The appropriate dose of ETV causing minimal tissue damage was determined by evaluating the mortality rate and extent of the lesions. Throughout the experiment, the mortality rates in gps (2, 3,4,5,6 and 7) were 3.13%, 6.25%, 21.88%, 6.25%, 6.25% and 6.25%, respectively. Microscopic examination of the liver revealed multiple areas of damage of the hepatic parenchyma which varied from cloudy swelling and hydropic degeneration to complete necrosis of the hepatocytes. Such areas were mostly subcapsular and paracentral. They were surrounded and mixed with eosinophils, macrophages and lymphocytes. In general, the hepatic lesions, encountered in the liver of the multiple infestation groups, were qualitatively similar to those demonstrated in the single infestation ones except for the eosinophilic infiltration which was more pronounced and the hepatocyte damage was milder. The hepatic parenchyma of the infestation groups (gps4 &7) showed TVL. Microscopically, the lungs revealed congestion and hemorrhages. Moreover, peribronchiolar and perivascular aggregations of eosinophils and round cells, which sometimes infiltrated the vascular wall, were noticed. Some alveoli were obliterated by eosinophils and round cells forming well pronounced granulomas, particularly supleural. Microscopically, the kidneys showed cortical and medullary congestion, together with cortical hemorrhage. Some renal blood vessels were surrounded by eosinophilic and round cell aggregations. The renal tubules showed degeneration and necrosis of their epithelial lining, particularly subcapsular. Focal cortical interstitial infiltrations with round cells and eosinophils, were observed. Microscopically, the heart showed little involvement in all the infested groups. Microscopically, moderate depletion of lymphocytes from the white pulp of the spleen was seen early in the single infestation groups, and hyperplasia was evident later on. However, the multiple infestation groups showed hyperplasia of the white pulp, which encroached over the red pulp at nearly all the experimental periods. Microscopically, the intestinal lesions were prevalent in the jejunum and ileum. The tips of the villi were clubshaped, with acelullar apical lamina propria. The epithelial lining of the crypts of Leiberkuhn was infiltrated with eosinophils. Paneth cells showed prominent eosinophilic granules. Focal infiltration of the tunica muscularis with eosinophils was seen. Frequent desquamation of the epithelial covering of the villi, particularly at the tips of villi, was encountered. Eosinophilic infiltrations were seen among the hyperplastic pericytes in the lamina propria. Microscopically, the brain showed mild or no lesions. The muscular involvement was mild in all the experimental groups. Our study culminated to the result that among the single and multiple infestation groups, the single inoculum dose of 200 ETV, showed the least tissue damage and the earliest tissue healing.