Feline leukemia virus (FeLV) is a retrovirus that progressively impairs immune function in infected cats, causing significant disease burden and welfare challenges over the course of infection.
FeLV infection creates a spectrum of welfare outcomes. Some infected cats remain relatively healthy for years before disease progression, while others develop rapid-onset severe illness. The immunosuppressive effects mean infected cats are vulnerable to opportunistic infections that healthy cats would resist, creating ongoing disease burden. The secondary conditions caused by immune compromise — recurrent infections, anemia, lymphoma — cause significant pain and debilitation. Management of FeLV-positive cats requires indoor-only housing to prevent viral spread, which limits behavioral opportunities for cats accustomed to outdoor access. Quality of life monitoring is important in FeLV-positive cats, with regular veterinary assessment helping owners recognize when declining health warrants end-of-life intervention.