Feline leukemia virus causes progressive immune suppression and cancer in cats, but vaccination and testing programs can prevent infection and protect cat welfare significantly.
FeLV causes a progressive deterioration in cat health that imposes sustained welfare costs over months to years. Immune suppression leaves cats vulnerable to infections they would normally resist, causing repeated illness episodes. Anemia causes chronic fatigue and weakness. Lymphoma causes pain and systemic illness in its terminal phase. The welfare obligation for FeLV-positive cats involves maximizing comfort and quality of life through attentive care while honestly assessing when the burden of disease outweighs the benefits of continued treatment. Prevention through vaccination is the most impactful welfare intervention — stopping infection before it occurs eliminates all subsequent suffering.