Feline leukemia virus is a serious retroviral infection of cats with welfare implications for affected individuals and populations, but effective vaccination has transformed prevention.
FeLV causes significant welfare harm through progressive immune failure and the development of lymphoma, anemia, and secondary infections that cause substantial suffering over months to years. Unlike FIV, persistently viremic FeLV-positive cats have a much poorer prognosis and genuinely require management including isolation from susceptible cats. Vaccination has dramatically reduced FeLV prevalence in populations where programs have been implemented. Welfare management for FeLV-positive cats focuses on maximizing quality of life while monitoring for and managing secondary complications.