Feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV): what a positive result means
A positive test for FeLV or FIV sounds like a death sentence, and for years it was treated as one. Today we know much more: they are not the same disease, they do not spread the same way, many FIV-positive cats live a normal life and a positive FeLV result needs confirming before any decisions are made.
Two different viruses, often confused
Feline leukaemia is caused by the FeLV virus and feline immunodeficiency by the FIV virus. Both are retroviruses, they are often detected with the same rapid test and they only affect cats: they do not spread to people, dogs or other pets. That is where the similarities end. FeLV spreads more easily, can cause serious diseases such as anaemia, lymphoma and leukaemia, as well as immunosuppression, and in its progressive form shortens life considerably. FIV spreads with more difficulty, progresses very slowly and many infected cats live for years, even with a life expectancy similar to a negative cat's, if they are well looked after.
How they spread
FeLV is shed mainly in saliva, and also in nasal secretions, urine, faeces and milk. It spreads through prolonged, friendly social contact: grooming each other, sharing food and water bowls, and from mother to kittens. It is more common in young cats, in cats with outdoor access or those living with many cats. FIV is transmitted mainly through deep bite wounds in fights, which is why it is more common in entire males with outdoor access; spread through peaceful living together, sharing bowls or grooming is very rare. Both viruses survive only briefly outside the cat and are inactivated by ordinary disinfectants.
The test: what it detects and why it needs confirming
The usual rapid test detects FeLV antigen in the blood, meaning the virus itself, and antibodies against FIV. The guidelines of the ABCD, the European advisory board of experts on feline diseases, recommend not making irreversible decisions on a single positive. A positive FeLV result in a healthy cat should be confirmed, ideally with PCR or by repeating the test a few weeks later, because some cats clear the virus. A positive FIV result in a kitten under six months may be due to antibodies passed on by the mother, and the test must be repeated after six months of age. And a recently exposed cat may test negative for a few weeks: if there has been risky contact, the test is repeated a month or two later.
FeLV: progressive, regressive or abortive
Not every cat infected with FeLV ends up the same way. In abortive infection, the immune system clears the virus and the cat is protected. In regressive infection, the cat controls the virus, stops shedding it and is usually healthy, although the virus stays integrated in its cells and can reactivate with stress or immunosuppression. In progressive infection, the virus is not controlled, the cat sheds it and over time develops associated diseases. Median survival after diagnosis in progressive cats is around a few years, but it varies widely and some live considerably longer with good care. Knowing which group your cat is in requires repeated testing, and that changes the prognosis.
FIV: a slow infection
After infection, FIV goes through an initial phase with mild or unnoticed symptoms, followed by a symptom-free phase that can last many years. Over time, in some cats, the immune system weakens and infections take hold more easily: of the mouth (gingivitis and stomatitis), skin, airways or gut, and some tumours. But many FIV-positive cats die of old age from other causes. What helps them most is an indoor life or safe outdoor access, no fights, good nutrition, check-ups every six months and treating any infection early.
Caring for a positive cat
Vet check-ups every six months, with weight, examination of the mouth, eyes and lymph nodes, and blood tests at least once a year. Core vaccines and parasite control according to their risk, tailored by the vet. Complete, balanced food, never raw meat or unpasteurised milk, because of the risk of infection. An indoor life or supervised outings: it protects the cat from infections and stops them spreading the virus to others. Neutering, which reduces fighting and roaming. Prompt treatment of any symptom, because secondary infections are what most wear these cats down. There is no routine antiviral treatment that eliminates these viruses; what makes the difference is care.
Living with other cats
With FIV, the ABCD guidelines consider that a positive cat can live with negative cats in a stable home without fighting, with a low risk of transmission; what matters is that there are no bites, so it is best not to put them with cats they do not get on with. With progressive FeLV, the risk of spreading it to other cats in the home is higher: the recommendation is that they live alone or with other cats that are also positive. If they already live together, negative companions should be vaccinated against FeLV, bearing in mind that the vaccine protects well but not one hundred per cent, and monitored with regular tests. A FeLV-positive cat should not go outdoors or join colonies.
Vaccines and prevention
Effective vaccines against FeLV exist. The WSAVA and ABCD guidelines recommend vaccinating kittens and young cats, and adults at risk, meaning those with outdoor access or living with cats that are positive or of unknown status, always after a negative test. There is no FIV vaccine available in Europe. Prevention means testing any new cat before introducing them to those at home, neutering to reduce fights and, if the cat goes out, vaccinating against FeLV. Cats that live alone indoors and never go out have a very low risk of both viruses.
What it costs
As a guide in Spain in 2026, the combined FeLV/FIV rapid test costs between 30 and 55 €, confirmatory PCR between 50 and 100 €, and the FeLV vaccine between 35 and 60 € per dose, with two initial doses and later boosters. A healthy positive cat mainly means more frequent check-ups, 100 to 250 € a year more than usual. Associated diseases, such as lymphoma or chronic stomatitis, can mean treatment costing from several hundred to several thousand euros. Many rescues rehome FIV and FeLV-positive cats, explaining their situation; these are cats that deserve a home and can live well with the right care.
FeLV and FIV are not the same: leukaemia spreads more easily and is more serious in its progressive form; immunodeficiency progresses slowly and many cats live a normal life. Always confirm a positive result before deciding anything, test every new cat and vaccinate cats that go outdoors against FeLV.
Educational content from Michipedia, translated from the Spanish original. It does not replace the advice of a vet or a feline behaviour specialist. Every cat is an individual.