Feline leukaemia virus infection affects the immune system and can cause cancer and anaemia, but vaccination has dramatically reduced its prevalence and many infected cats live well with appropriate monitoring.
FeLV-positive cats face a range of welfare outcomes depending on their infection status and health at diagnosis. Progressively infected cats — those with persistent antigenaemia — face elevated risk of lymphoma, anaemia, and immunosuppression-related disease that reduces life expectancy and imposes welfare burdens over time. However, many FeLV-positive cats remain healthy for years after diagnosis and maintain excellent quality of life with appropriate management. The welfare priorities for FeLV-positive cats include indoor housing to prevent exposure to infections their compromised immunity cannot handle, regular veterinary monitoring to detect early signs of disease, prompt treatment of secondary infections, and honest quality of life assessment when disease does progress. Early euthanasia decisions for newly diagnosed FeLV-positive cats that are otherwise healthy are inappropriate — the diagnosis does not predict imminent or severe welfare compromise in most individual cases. Rescue organisations that adopt FeLV-positive cats and provide appropriate management serve an important welfare role by reducing their overrepresentation in euthanised shelter populations.