Myeloid leukosis is a type of cancer that affects the blood and bone marrow, primarily seen in birds, especially in chickens. It is caused by a virus known as the avian leukosis virus, which leads to the uncontrolled growth of myeloid cells, a type of white blood cell. This condition can result in various symptoms, including lethargy, weight loss, and swelling of the abdomen. The disease is typically diagnosed through blood tests and examination of bone marrow samples. Prevention strategies include good management practices and vaccination against the avian leukosis virus. Early detection and intervention are crucial for improving the health outcomes of affected birds.