Last updated: 28 September 2026
FIV (feline AIDS) and FeLV (feline leukaemia) are two retroviruses that infect only cats and can remain without symptoms for years. According to the American Association of Feline Practitioners (AAFP), every cat should be tested when it moves into a new home, after contact with an infected cat or a cat of unknown status, and when it is ill. A combined rapid test using a blood sample gives a result within minutes; a positive result is confirmed by a vet.
Below we summarise how the two viruses differ, how they spread, when and how to test, and what a positive test means.
What is the difference between FIV and FeLV?
Both are retroviruses, but they spread differently, follow a different course, and the rapid test detects something different for each: for FIV the antibodies produced by the body, for FeLV the viral protein itself (antigen).
| Feature | FIV (feline AIDS) | FeLV (feline leukaemia) |
|---|---|---|
| Main route of transmission | Bites, mainly in fighting tomcats that go outdoors | Saliva: mutual grooming, shared bowls; from mother to kittens |
| What does the rapid test detect? | Antibodies against FIV | FeLV antigen (p27 protein) |
| When can it be detected after infection? | Usually within 60 days | Usually within 30 days |
| Course | Slow; many cats have no symptoms for years | More severe in persistent (progressive) infection: anaemia, tumours, immunodeficiency |
| Survival after diagnosis (AAFP) | Median 4.9 years (negative cats: 6.0 years) | Median 2.4 years in progressive infection (negative cats: 6.3 years) |
| Vaccine in Europe | Not available (ABCD) | Available, recommended depending on risk |
Both viruses infect only felines: they do not spread to humans, dogs or other pets.
How common is FeLV in Europe?
In a study covering 30 European countries, published in 2019, FeLV was detected in the saliva of 2.3% of cats; in Hungary the rate was 5.9% (18 of 305 cats), the second highest after Portugal (Studer et al., Viruses, 2019). The researchers looked for the virus in saliva samples using PCR, so they identified cats that were shedding the virus.
This means that in a cat with an unknown background, an adopted cat or an outdoor cat, infection is a realistic possibility, even if the cat looks completely healthy.
How are FIV and FeLV transmitted?
FIV spreads mainly through bites, FeLV mainly through saliva during close contact.
- FIV: according to ABCD (European Advisory Board on Cat Diseases), the main route of transmission is biting during fights. Outdoor, unneutered, territorial tomcats are most at risk. According to the AAFP, the risk of infection is negligible in stable households where cats do not fight.
- FeLV: a persistently infected cat sheds large amounts of virus in its saliva. It spreads through mutual grooming and shared food and water bowls, less often through shared litter trays and bites, and from mother to kittens during pregnancy, birth and nursing.
What are the symptoms of FIV and FeLV?
For a long time, none: both infections can remain without symptoms for years, so you cannot tell by looking whether a cat is infected. When symptoms do appear, they are not specific to these two diseases:
- recurring upper respiratory infections, conjunctivitis,
- gum and mouth inflammation, bad breath,
- weight loss, dull coat, loss of appetite,
- anaemia, pale mucous membranes, weakness,
- enlarged lymph nodes, persistent fever,
- tumours, especially lymphoma, mainly with FeLV.
If any of these keeps coming back or is slow to heal, it is worth testing for both FIV and FeLV.
When should you do an FIV/FeLV test?
According to the AAFP's 2020 guidelines, every cat should be tested as soon as it arrives in a new home, after contact with an infected cat or one of unknown status, before FeLV vaccination, and when it is ill.
| Situation | When to test? | What to watch out for? |
|---|---|---|
| A new cat arrives (adoption, purchase, taking in a stray) | On arrival, before it meets your other cats | If negative, repeat after 60 days, as a recent infection cannot yet be detected. |
| Fight, bite, contact with an unknown cat | As a baseline after the incident, then again after at least 60 days | FIV antibodies usually appear within 60 days. |
| A sick cat or one that is repeatedly unwell | When symptoms appear | A negative test does not rule out illness from other causes. |
| Before FeLV vaccination | Before the first vaccination | The vaccine does not protect against an existing infection. |
| FIV-positive kitten under 6 months | Repeat after 6 months of age | Antibodies from the mother can cause a false positive FIV result. |
| Breeding cat | Before breeding and when introducing a new cat | Document the result and pass it on to the buyer. |
How does the home FIV/FeLV rapid test work?
The combined rapid test uses a small amount of blood, serum or plasma to check for FIV antibodies and FeLV antigen at the same time, on two separate test lines. It is best to leave blood sampling to a vet; the reading time is given in the manufacturer's instructions.
According to the manufacturer's validation, the MancsLab FIV Ab/FeLV Ag rapid test has a sensitivity of 96.88% and a specificity of 98.13% for FIV (compared with ELISA, on 320 samples), and a sensitivity of 97.77% and a specificity of 97.05% for FeLV (compared with PCR, on 350 samples). What these numbers mean in practice is explained here: How accurate is a home rapid test?
| What you see | Result | What to do |
|---|---|---|
| C line and FIV line | FIV antibody positive | Confirmatory test at the vet. In kittens under 6 months, repeat after 6 months of age. |
| C line and FeLV line | FeLV antigen positive | Separate the cat from your other cats and ask for a confirmatory test. |
| Only the C line | Negative | After recent exposure, repeat after 60 days. |
| No C line | Invalid | Repeat with a new cassette. |
Even a faint test line counts as a positive result.
What does a positive FIV or FeLV test mean?
A positive rapid test is a strong signal, but not a final diagnosis: both the AAFP and ABCD recommend a confirmatory test, especially in low-risk cats, where false positives make up a larger share of positive results.
- FeLV: confirmation is done with a laboratory p27 antigen ELISA or PCR, which detects the virus's genetic material. FeLV infection can have several outcomes: some cats suppress the virus (regressive infection), others remain persistently infected (progressive infection). That is why your vet may request a repeat test a few weeks later.
- FIV: confirmation is done with a different method; according to ABCD, Western blot is considered the "gold standard", but PCR can also be used. In kittens under 6 months, because of antibodies from the mother, a positive result must be rechecked after 6 months of age.
Can positive and negative cats live together?
An FIV-positive cat can live with negative cats in a calm group that does not fight, but according to the AAFP an FeLV-positive cat must be separated from uninfected cats.
- FIV-positive cat: according to the AAFP, the risk of infection in stable, fight-free households is negligible. When introducing a new cat, watch how they get on and ask your vet for advice.
- FeLV-positive cat: keep it apart from negative cats, with its own bowls and litter tray. According to ABCD, keeping it strictly indoors extends its life and prevents the infection from spreading further. Talk to your vet about vaccinating the negative cats against FeLV.
- In both cases: keeping the cat indoors reduces the chance that a cat with a weakened immune system catches another infection or passes on the virus.
How long does an FIV- or FeLV-positive cat live?
FIV-positive cats often live an almost normal lifespan, whereas cats persistently infected with FeLV have a shorter life expectancy. According to data cited by the AAFP, median survival after the first positive test was 4.9 years for FIV-positive cats (6.0 years for negative cats) and 2.4 years for cats with progressive FeLV infection (6.3 years for negative cats).
Quality of life is greatly improved by keeping the cat indoors, a stress-free environment, good-quality nutrition, regular vet check-ups, and having every minor illness (cat flu, diarrhoea, gum inflammation) treated promptly.
Which test should you choose when a new cat arrives?
For a new cat, the combined FIV/FeLV test is the basic test. If the kitten has diarrhoea, the FPV Ag (panleukopenia) rapid test and the Giardia rapid test are also worth considering. We describe the full screening process for adoption here: Adopting a cat: what you need to know about screening tests. All cat tests in one place: rapid tests for cats.
Frequently asked questions about FIV and FeLV
Can humans or dogs catch FIV or FeLV?
No. Both viruses infect only felines and do not spread to humans, dogs or other pets.
How soon after infection does the test detect it?
According to the AAFP, FeLV antigen can be detected in most cats within 30 days and FIV antibodies within 60 days. That is why, after recent exposure, a negative test should be repeated after at least 60 days.
Why can a kitten be FIV-positive if it is not infected?
Because antibodies received from an infected mother can be detected in its blood up to 6 months of age. If the kitten is still FIV-positive after 6 months of age, it is probably truly infected.
Is there a vaccine against FIV and FeLV?
An FeLV vaccine is available in Europe and is recommended depending on the cat's risk; the cat must be tested before it is given. According to ABCD, there is currently no FIV vaccine available in Europe.
The test was negative. Is my cat definitely not infected?
Very probably not, but an infection that happened a few weeks ago cannot yet be detected. If your cat has been in a fight in the past 2 months or has lived with a cat of unknown status, repeat the test after 60 days.
Summary
FIV and FeLV can stay hidden for years, so every new, sick or exposed cat should be tested before it meets the others. A positive rapid test should be confirmed by a vet; with the right care a positive cat can live well for a long time, and the other cats can be protected.
Sources
- Little S, et al.: 2020 AAFP Feline Retrovirus Testing and Management Guidelines. Journal of Feline Medicine and Surgery, 2020. journals.sagepub.com
- ABCD – European Advisory Board on Cat Diseases: Guideline for Feline Leukaemia Virus Infection. abcdcatsvets.org
- ABCD – European Advisory Board on Cat Diseases: Guideline for Feline Immunodeficiency Virus. abcdcatsvets.org
- Studer N, et al.: Pan-European Study on the Prevalence of the Feline Leukaemia Virus Infection. Viruses, 2019;11(11):993. mdpi.com
- Manufacturer's validation data (FIV Ab/FeLV Ag rapid test). product page
Important: this article provides general information and does not replace veterinary advice. Confirmatory testing, treatment and living arrangements must always be decided by a vet. MancsLab rapid tests are intended for preliminary screening at home.