Feline leukemia virus (FeLV) causes progressive immune dysfunction and cancer in affected cats, with vaccination providing excellent protection for at-risk individuals.
FeLV causes progressive welfare decline through anemia, recurrent infections, and ultimately cancer. Anemia causes weakness, lethargy, and reduced exercise tolerance that progressively limits quality of life. Immune suppression means every bacterial or viral challenge that a healthy cat would overcome easily can cause serious illness in an FeLV-positive cat. The eventual development of lymphoma or other cancers causes significant suffering requiring palliative or curative oncology treatment. Despite this, FeLV-positive cats can have good quality of life for extended periods with appropriate supportive care, and their welfare needs deserve the same attention as any other cat.