Feline leukemia virus causes immunosuppression and cancer in cats, but is entirely preventable through vaccination and testing protocols that protect individual cats and colonies.
FeLV-positive cats face an uncertain future - progressive infection leads to immunosuppression, anemia, and cancer within months to years. The chronic suppression of immune function causes repeated infections and illness. Regressive infection can reactivate under stress, creating ongoing welfare uncertainty. The tragedy of FeLV is that it is largely preventable through testing and vaccination, yet continues to affect cats in multi-cat households and colonies where prevention is not practiced.