Abstract
Background:
Pigeon leukosis is primarily caused by avian leukosis virus subgroup A (ALV-A). It infects and transforms lymphoid cells, leading to the development of tumors in various lymphoid tissues and other organs especially the liver.
Aim:
This study was conducted to diagnose lymphoid leukosis in a naturally infected pigeon flock in Egypt.
Methods:
Tissue specimens from the liver, spleen, thymus, kidney, lung, proventriculus, gizzard, intestine, pancreas, heart, pectoral muscle, ovary, and testes were collected from infected birds for pathological and immunohistochemical examinations.
Results:
Clinical signs were generally non-specific and comprised weakness, dehydration, and emaciation. Gross lesions were mostly in the liver and spleen, in the form of minute white nodules scattered on the liver surface. Microscopic examination of the liver, spleen, and kidneys showed masses of uniform sizes and the presence of differentiated lymphoid cells. These cells appeared as large mononuclear cells with poorly defined cell membranes. Immunohistochemical investigation exhibited that the ALV-A positive indicators were chiefly accessible in the liver, ovary, spleen, and kidney.
Conclusion:
Lymphoid leukosis in pigeons could be provisionally diagnosed by a pathological picture of characteristic tumors and confirmed by immunoreactivity of viral antigens in different tissues.

Key words: Pigeon, Lymphoid leukosis, Pathology, Immunohistochemistry