New insights into recently emerged Leucocytozoon caulleri infection in Egyptian broiler flocks through clinical, pathological, hematological, and molecular investigation.

Leucocytozoonosis is a vector-borne blood protozoal disease that affects birds worldwide. Although Egypt has a large-scale poultry industry, data on Leucocytozoon infections in broilers remain limited. This study reports the first detection of leucocytozoonosis in 24 broiler farms (180,000 birds) in El-Sharkia governorate, Egypt. The affected broiler flocks were raised in open poultry farms located near agricultural rice fields and water sources during the late summer season, which are conditions favorable for vector proliferation. Clinically, infected birds exhibited depression, anorexia, weight loss, and anemia, with mortality rates ranging from 0.5% to 2%. Postmortem examination revealed widespread hemorrhages across multiple organs and a large pool of blood in the abdominal cavity. Microscopic examination of blood smears and cell block preparations showed the presence of various gametocytes within leukocytes and erythrocytes. Histopathological examination identified characteristic megaloschizonts in multiple organs, including the kidneys, liver, lungs, muscles, heart, intestine, pancreas, and spleen, accompanied by hemorrhages, necrosis, and mononuclear cell infiltration, primarily lymphocytes and macrophages. Molecular identification using real-time PCR confirmed L. caulleryi infection, corroborating the hematological and pathological findings. This study provides key insights into L. caulleryi diagnosis, promotes awareness among veterinarians and poultry producers, and highlights the need for improved biosecurity.