Cat Feline Leukemia Virus: Prevention Through Vaccination and Testing

Feline leukemia virus is a major cause of illness and death in outdoor cats. Testing and vaccination dramatically reduce its welfare impact.

Key Facts

FeLV is a retrovirus causing immunosuppression, anemia, and tumors in infected cats
It is transmitted primarily through close social contact — mutual grooming, shared food bowls, and biting
Approximately 2-3% of cats in developed countries are FeLV positive; rates are higher in strays and feral populations
Vaccination provides significant protection — FeLV is a non-core vaccine recommended for outdoor or at-risk cats
Progressive infection leads to persistent viraemia, immunosuppression, and eventually death in most cases
Cats with regressive infection (FeLV-R) may clear the virus without progressing to persistent infection

Welfare Considerations

FeLV causes progressive illness — cats with progressive infection face increasing immunosuppression, secondary infections, and tumours leading to death. Welfare-centred FeLV management involves testing new cats before introducing them to FeLV-negative households, vaccination of outdoor and at-risk cats, and compassionate management of positive cats including prompt treatment of secondary infections and quality of life assessment as disease progresses. FeLV-positive cats require indoor housing to prevent transmission and to protect their compromised immune systems. Negative prognosis should be communicated honestly to enable timely end-of-life decisions.

What You Can Do

Test all new cats for FeLV and FIV before introducing them to resident cats
Vaccinate outdoor and multi-cat household cats against FeLV — it is not a core vaccine but highly recommended
Keep FeLV-positive cats indoors to prevent transmission and protect their immune system
Provide FeLV-positive cats with excellent nutrition and preventive care to maintain immune function
Monitor for secondary infections and address them promptly — immunosuppressed cats deteriorate quickly if untreated