Abstract
Background:
Avian coccidiosis is one of the most significant and impactful diseases affecting the commercial poultry industry globally.

Aim:
This study aimed to identify the Eimeria species associated with chicken coccidiosis.

Methods:
Conducted from November 2023 to April 2024, the research involved 150 avian samples. Intestinal samples were collected from chickens suspected of having coccidiosis at veterinary hospitals and clinics in Diwaniyah Governorate. To confirm the infection, a longitudinal incision was made in the ceca of the suspected infected chicken, and a direct swab was obtained. Part of the cecal contents was placed in a test tube for the fecal flotation method, while the remainder was stored in a separate test tube and refrigerated for DNA extraction. Additionally, a 1-cm tissue sample was collected from the cecum and preserved in formalin to assess histopathological changes. Samples were analyzed using microscopy and conventional polymerase chain reaction (PCR), focusing on the small subunit 18S rRNA gene of the parasite, specifically internal transcribed spacer 1.

Results:
Microscopic analysis revealed parasitic oocysts in 19.3% of the fecal samples from the examined poultry. Furthermore, the PCR results indicated that Eimeria tenella was present in 22% of the fecal samples. The internal transcribed spacer-1 sequences of E. tenella from this study showed a high degree of similarity to those recorded in GenBank at 95%, with sequences from India (GQ856301, JX853825.1, JX853831.1, PP002176.1), China (JX477100.1, FJ449692.1, GQ153631.1, FJ449691.1), and Turkey (HQ680474.1) species. Overall, Eimeria tenella, which causes coccidiosis in poultry, leads to significant histopathological alterations in the intestinal tissues of infected birds, including epithelial damage.

Conclusion:
This study concludes that E. tenella is present in the tested poultry within the governorate.

Key words: Broiler, Eimeria tenella, Iraq, PCR, Poultry