Background: Coccidiosis is a major parasitic disease that poses significant economic challenges for sheep, particularly in lambs. This case report outlines an occurrence of clinical coccidiosis impacting lambs on a sheep farm situated in the Chenaran region of Khorasan Razavi Province. Methods: In October 2024, a clinical coccidiosis outbreak was documented among weaned lambs of the Lacaune breed at a sheep farm in the Chenaran area. This group consisted of 272 lambs, all approximately 2-3 months old. The affected lambs displayed symptoms such as anorexia, weight loss, weakness, and severe diarrhea, which was sometimes bloody. Parasitological and pathological examinations were conducted to confirm the diagnosis. Results: The mean ± SD of OPG for diarrheic and non-diarrheic lambs showed no significant difference (P>0.05). Three species of Eimeria were identified: 1- Eimeria palida, which has a colorless appearance and lacks a micropyle (15-17.5 × 11-12.5µm); 2- Eimeria ovinoidalis, which is ellipsoidal, colorless, and also lacks a micropyle (20-27 × 15-20 µm); and 3- Eimeria intricata, which is ovoid, yellow, has a thick wall, and features an operculum (47.5-50 × 30-37.5 µm). Histopathological analysis of the intestinal samples revealed various developmental stages of Eimeria within the glandular epithelial cells of the caecum. Other general microscopic findings were severe hyperemia, edema, hemorrhage, infiltration of inflammatory cells, and glandular epithelial lesions such as degeneration and necrosis Conclusion: The clinical and pathological findings validated the diagnosis of clinical coccidiosis in the affected weaned lambs; the parasitological results indicated that E. ovinoidalis was the primary species responsible for the clinical coccidiosis.

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