FIV: feline immunodeficiency virus
A lifelong infection that is far more manageable than most owners expect.
Key points. FIV is spread mainly by bite wounds, not by sharing bowls or cuddling. Many FIV-positive cats live for years with few problems. A healthy cat should never be euthanased solely because of a positive FIV test. Keep the cat indoors, neutered, and see a vet regularly.
What it is
Feline immunodeficiency virus is a retrovirus (a lentivirus) that infects a cat's white blood cells. Over time it can weaken the immune system, so that infections and other conditions that a healthy cat would shrug off become more difficult to control. It is related in type to the human immunodeficiency virus, but it is a cat virus: it is species-specific and is not a threat to people.
Infection is lifelong. There is no cure, but infection and illness are not the same thing: many infected cats never develop serious immune deficiency.
How it spreads and how contagious it is
- Bite wounds are the main route. The virus is present in saliva, and deep bites from fighting transfer it. Unneutered, free-roaming adult males are at highest risk.
- Casual contact is not an efficient route. Sharing food bowls or mutual grooming is considered a minor route at most. The virus is fragile outside the cat and is killed by ordinary disinfectants.
- Mother to kittens transmission can happen but is uncommon; only some kittens of infected queens become persistently infected.
- Stable households where cats do not fight show a low risk of spread, according to International Cat Care and the ABCD.
- Prevalence is roughly 2.5 to 5 percent in healthy cats in North America, and higher (15 percent or more) in sick or high-risk cats (Cornell). Rates vary widely by country.
Signs and course
After infection there is often a long period with no signs at all. Where disease does develop, it often appears years later (the ABCD gives roughly 4 to 6 years of age or older; International Cat Care says around 2 to 5 years after infection). Cats infected young, and cats living in crowded conditions, tend to progress faster.
Possible signs of immune weakness include:
- weight loss, recurrent fever, lethargy;
- swollen lymph nodes;
- inflamed gums and mouth (gingivitis and stomatitis);
- repeated or slow-to-resolve infections of the skin, eyes, nose or bladder;
- in some cats, cancers or neurological changes.
None of these is specific to FIV, so testing is needed to know the cause.
Testing and diagnosis
- The usual screening test is a quick blood test (ELISA or point-of-care) that detects antibodies to the virus. It can be run at the clinic.
- Antibodies take time to appear. A negative result soon after possible exposure may be wrong, so the test is repeated about 2 months later if the cat might have been recently infected.
- In low-risk cats (for example young indoor pedigree cats), a positive screening result should be confirmed with a second test such as Western blot or PCR before acting on it. False positives are more likely when true prevalence is low.
- Kittens under about 6 months can test positive because they carry antibodies from their mother, not because they are infected. Recommended retesting is at around 6 months (Cornell; International Cat Care), or at about 16 weeks and again two months later if still positive (ABCD). A positive result after 6 months is very likely to be real infection.
- Vaccinated cats also test positive on antibody tests (see vaccines), so vaccination history matters.
- If one cat in a home is found positive, all cats in the home should be tested.
Prognosis
Outlook depends on the stage of disease and on whether the cat has other illnesses. Many FIV-positive cats have an apparently normal life expectancy, particularly in stable, low-stress homes. Prognosis becomes less favourable after serious secondary disease or with persistent fever and weight loss. Cats that also carry FeLV do worse.
The ABCD states plainly that healthy seropositive cats should never be euthanised. Many rescues now rehome FIV-positive cats successfully.
Day-to-day care
- Neuter the cat. This reduces roaming and fighting.
- Keep the cat indoors, or give outdoor time only in a secure enclosure or on a lead. This protects other cats from the virus and protects your cat from infections picked up outside.
- Check-ups at least every 6 months, with weighing at each visit; a blood count, biochemistry and urine test about once a year are commonly advised (Cornell).
- Feed a complete, balanced commercial diet. Avoid raw meat, raw eggs and unpasteurised dairy, because infections from these are harder for an immunocompromised cat to handle.
- Keep up parasite control (fleas, worms) and dental care. See everyday care.
- Treat illness early. A cat with FIV may need longer or stronger courses of treatment, so do not wait and watch. Mention FIV status at every vet visit.
- Vaccination is individual: see vaccines for FIV and FeLV positive cats.
- Antiviral drugs are of limited value. Zidovudine (AZT) is sometimes used for mouth inflammation or neurological signs but does not extend survival and has side effects (Cornell). Ask your vet whether any such medicine suits your cat.
- Reduce stress: stable routines, enough litter trays and resting places, and gentle play. See stress reduction.
When to call a vet urgently: breathing difficulty, collapse, a cat that is straining to pass urine or producing none, repeated vomiting, not eating for 24 hours or more, or sudden weakness in the back legs. See signs that need a vet urgently.
Can an FIV-positive cat live with FIV-negative cats?
Guidance says "ideally, separate", but in practice the risk is much lower when cats do not fight:
- Cornell advises separating infected and uninfected cats where possible, while noting that the risk is much lower in households where cats do not fight.
- International Cat Care says that in stable homes where cats do not fight the risk of spread is low, and suggests discussing separation, separate bowls and regular disinfection with your vet.
- The ABCD suggests segregating positive and negative cats if unsupervised fights are likely, and advises against adding new cats to a household that includes an infected cat, since newcomers can trigger fighting.
- Neutering all cats, a calm household and enough resources (bowls, trays, beds, hiding places) help.
- If other infectious diseases are circulating in the household, isolating the FIV-positive cat may be sensible because its immune system is less able to cope.
Introduce cats gradually and watch the first weeks closely. If scuffles occur, keep them apart and ask your vet or a qualified behaviourist.
Is there an FIV vaccine?
No FIV vaccine is commercially available in North America (it has not been sold there since 2016) or in Europe. It has been available in some other countries, including Australia, New Zealand and Japan. International Cat Care notes that it cannot be expected to give complete protection because several FIV strains exist, and the ABCD does not recommend the whole-inactivated-virus vaccine sold outside Europe because of the diagnostic problems it causes and limited evidence that it protects against field strains.
A vaccinated cat will produce antibodies that standard tests cannot distinguish from natural infection. In one Australian study these persisted for up to 6 months; other reports describe longer periods. A positive test in a vaccinated cat should be followed up with PCR. If your cat has ever been vaccinated against FIV, tell your vet and any rescue.
People and dogs
FIV infects only cats. There is no evidence that it infects or harms humans, and it is not known to infect dogs. You can safely cuddle, groom and care for an FIV-positive cat.
Sources
- Cornell Feline Health Center: Feline Immunodeficiency Virus
- International Cat Care: Feline immunodeficiency virus (FIV)
- ABCD (European Advisory Board on Cat Diseases): Feline immunodeficiency guidelines
- AAFP: Feline Retrovirus Management Guidelines (2020) - summary page with link to the full guideline