You take in a street cat, the vet runs a quick blood test, and one of the little windows shows a line. FIV positive. Or FeLV. It’s easy to hear that as the end of the story.
It usually isn’t. These are two different viruses that spread in different ways and do very different things. Here’s what each one means, in plain words.
The short version
- FIV spreads mainly through deep bites, usually in fights between unneutered toms.
- FeLV spreads through close, friendly contact: grooming, shared bowls, mothers to kittens.
- Many cats with FIV live long, normal lives.
- FeLV is more serious, but some cats live with it for years.
- A positive test alone is not a reason to put a healthy cat down.
- People can’t catch either virus.
Two different viruses
FIV is feline immunodeficiency virus. It slowly weakens a cat’s immune system, the body’s defence against infection, often over many years. It’s a cousin of HIV, but it only infects cats.
FeLV is feline leukaemia virus. It can also weaken the immune system, and it can cause anaemia (too few red blood cells) and cancers such as lymphoma. It’s the more dangerous of the two.
Neither is rare, and street cats don’t seem to have them much more often than pets. A study cited by Alley Cat Allies found FeLV in 4.3% and FIV in 3.5% of community cats, similar to owned cats. In a European study cited in the vets’ guidelines, FeLV was most common in southern Europe, at 5.5% of cats tested, and least common in the north, at 0.7%.
How FIV spreads: bites
The main way FIV passes from cat to cat is through bite wounds, when infected saliva gets deep under the skin. That’s why it’s a fighters’ virus. Cornell’s Feline Health Center says the cats most at risk are unneutered males that go outside and are likely to fight, and International Cat Care says infection is about twice as common in males as in females.
Friendly contact rarely spreads it. Sharing bowls and grooming each other don’t seem to be an efficient way to pass it on, and mothers rarely pass it to their kittens. The vets’ guidelines say cats in calm households where nobody fights are at negligible risk.
How FeLV spreads: friendship
FeLV is the opposite. It’s mostly in saliva, and it spreads through the close contact friendly cats have: grooming each other, sharing food bowls and litter trays. Bites can spread it too, and a mother can pass it to her kittens. Kittens are the most likely to become infected for good.
Not every cat that meets FeLV keeps it. Some fight it off completely. Some keep it in check without getting rid of it. Others become permanently infected and shed the virus, and those are the cats that get ill.
Testing
Most vets use a quick blood test in the surgery that checks for both. A positive result is a reason to look more closely, not a final answer. The 2020 guidelines from the American Association of Feline Practitioners, endorsed by the International Society of Feline Medicine, say a single test may not settle it, and repeat testing by a different method may be needed.
- Kittens and FIV. Kittens can test FIV positive because they carry their mother’s antibodies, not the virus. International Cat Care says to test them again at five to six months.
- FeLV can change. A cat that tests FeLV positive may fight the virus off. A repeat test after some weeks shows which way it went.
- Vaccines can confuse it. In countries that use an FIV vaccine, a vaccinated cat can test positive on the usual test.
Who gets tested depends on the cat. The guidelines say pet cats should be tested when they join a home, after contact with a cat whose status isn’t known, and whenever they’re ill. For street cats in trap, neuter and return programmes, they recommend against routine testing, and so does Alley Cat Allies. The money is better spent neutering more cats.
A positive cat can live a good life
This is the part people most need to hear. The AAFP guidelines say some infected cats, especially those with FIV, can live for many years with good quality of life. Several studies they cite found FIV made no real difference to how long cats lived. Cornell says cats with FIV commonly live average lifespans, as long as they don’t also have FeLV.
FeLV is harder. Cats that are permanently infected usually live shorter lives. International Cat Care estimates that 80 to 90% die within three to four years of diagnosis. But many still have good months and years, and get ill only later.
Either way, the guidelines are clear: a diagnosis should not be the sole reason to put a cat to sleep. Alley Cat Allies doesn’t support killing FIV or FeLV positive cats who are healthy. A positive test is something to manage, with a vet, not a sentence.
Caring for a positive cat
- Neuter it. Neutered cats roam and fight less, which protects them and stops them passing FIV on.
- Regular vet checks. Problems like gum disease or infections are easier to treat if they’re caught early.
- Good food, little stress. A calm home with few other cats suits them best. In one study, FIV positive cats in crowded sanctuaries got ill far more often than those living alone or in pairs.
- Indoors if possible. International Cat Care recommends keeping FIV and FeLV positive cats indoors, which protects them from infections and other cats from them.
- For FeLV, protect the others. The guidelines recommend keeping a FeLV positive cat apart from uninfected cats, and vaccinating those cats against FeLV. Ask your vet.
The viruses don’t last long outside a cat. The guidelines say they’re inactivated within a very short time on dry surfaces, and ordinary disinfectants kill them.
Questions people ask
Can humans catch FIV or FeLV?
No. Both are cat-only viruses. Alley Cat Allies says neither can be passed to humans or other animals.
How long can a cat with FIV live?
Often a normal lifespan. Cornell says cats with FIV commonly live average lifespans, as long as they don’t also have FeLV.
Should a cat that tests positive be put to sleep?
Not for that reason alone. Vet guidelines endorsed by the International Society of Feline Medicine say a diagnosis should not be the sole reason for euthanasia, and many positive cats live well for years.
This guide is general information, not veterinary advice. If your cat tests positive, talk to your vet about confirming the result and about its care.
Snap the cats on your street and you’ll know the regulars: who’s new, who’s a fighter, and who still needs neutering.
