Lymphoid leukosis is a viral disease primarily affecting chickens, caused by the avian leukosis virus. It leads to the uncontrolled growth of lymphoid cells, which can form tumors in various organs, particularly the liver and spleen. Infected birds may show symptoms such as weight loss, lethargy, and swelling of the abdomen. The disease is transmitted through direct contact with infected birds or contaminated environments. Lymphoid leukosis can significantly impact poultry production, leading to economic losses for farmers. Vaccination and biosecurity measures are essential for preventing the spread of this disease in poultry flocks.