Abstract This study was conducted to investigate the pathogenesis process of E. ahsata and its morphological, pathological, and distribution of lesions in the involved tissues during 42 days of infection. Twelve lambs were provided and randomly divided into two groups including the control and the infected groups after confirmation of their health. The animals in the experiment group were orally infected with 1× 105 sporulated oocysts. From 7 days after inoculation (DAI), the faeces were sampled and oocysts per gram of faeces (OPG) were individually examined for each lamb. At 7, 14, 21, 28, 35 and 42 DAI, one lamb from each group was scarified and necropsied and the abomasum, small and large intestine, mesenteric lymph nodes, spleens and livers were grossly investigated. From 21 to 42 DAI, the mild to severe clinical lesions such as congestion and edema were seen on the mucosal surface of small intestine associated with white and small foci about 1-2 mm, especially jejunum and ileum. From 7 DAI to end of the study various stages of the parasite life cycle, infiltration of inflammatory cells, villi epithelial hyperplasia, and destruction of villi epithelium was seen. The results showed that E.ahsata was pathogenic in lambs and the macro and microscopic lesions were mostly seen in the jejunum

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