Feline leukemia virus is a devastating retrovirus that is largely preventable through vaccination and testing, yet remains a significant welfare burden in outdoor cats.
FeLV causes progressive immune system destruction, leaving cats increasingly vulnerable to infections and cancers that would not threaten healthy cats. Affected cats suffer from recurrent infections, severe anemia, and eventually the welfare impacts of FeLV-associated lymphoma or other malignancies. The tragedy of FeLV welfare harm is that it is largely preventable: vaccination of outdoor cats, testing before multi-cat household introduction, and keeping FeLV-positive cats separate from negative cats would dramatically reduce disease burden. FeLV-positive cats can live comfortable lives for years with appropriate management, but their welfare is chronically compromised by the immune suppression that the virus causes.