77 | How FeLV and FIV actually affect your patient - and the exact care they need
Patients with infectious diseases can be challenging to care for, especially when we’re juggling critical conditions while not being able to get as close to our patients as we’d like.
Over the next few episodes, we’ll dive into diseases like feline infectious peritonitis, brucellosis, tick-borne diseases, leptospirosis, parvovirus and much more - but today we’re kicking things off with two of the most common feline infections we see - feline leukaemia virus and feline immunodeficiency virus, aka FeLV and FIV.
If you’ve ever found yourself nursing a stray cat with suspicious bite wounds, or you’ve had a patient test positive on a SNAP test and thought ’What now?’ this episode is for you.
We’ll discuss what these diseases are, how they differ, and how they impact our patients, as well as the nursing care and client education that affect our patients’ quality of life - so you can spend less time feeling unsure about their disease, and more time focusing on giving great care.
First things first - what actually IS FeLV and FIV? And how do they differ?!
FeLV and FIV are often lumped together because they’re caused by similar viruses and are tested for simultaneously; however, in reality, they’re very different conditions, each with its own clinical signs, treatment considerations, and prognosis.
Let’s start with FIV.
Feline immunodeficiency virus, or FIV, is a retroviral infection caused by the FIV lentivirus. It is closely related to HIV in people, and FIV can infect various felidae species, including big cats. There are five genetically distinct subtypes of FIV found throughout the world. For example, all UK cats have FIV subtype A, whereas subtype D has been documented in Japan.
Between 2.5% and 14% of healthy cats worldwide are estimated to be FIV-positive, with transmission commonly occurring through bite wounds. Fighting and mating are significant risk factors, making this disease particularly prevalent in entire male cats, who are more likely to roam, defend territory and fight as well as mate. It’s also more common in shelters and hoarding environments.
FIV is NOT spread through social or non-confrontational contact like grooming or sharing water or food bowls - that is a particular misconception about FIV, and one which has led us to believe that FIV-positive cats cannot live alongside FIV-negative ones at times. There are quite a few myths about caring for FIV-positive cats, and we’ll debunk those throughout the episode today.
The FIV virus lives for very short periods - in fact, just a few minutes - outside of the host, and can be easily removed with detergents and disinfectants. In general, diseases that spread via direct contact (e.g., biting and fighting) are easier to eradicate from the environment and are much less likely to spread in a veterinary setting.
So what happens when a cat gets infected with FIV?
After infection, the FIV virus inserts a copy of its DNA into the host’s cell, where the genetic material mixes with the host’s DNA. The body then processes the viral DNA along with its own, making proteins that allow the virus to replicate - proteins that we test for during diagnosis.
FIV slowly weakens the immune system over time, making infected cats prone to secondary infections. Similar to human immunodeficiency virus, cats do not die from FIV itself, but from secondary infection, or advanced disease where the immune system becomes severely compromised (acquired immunodeficiency syndrome/AIDS).
It’s important to note that not all FIV-positive cats will develop AIDS, and most will live happily with a good quality of life for many years (and sometimes for life) as long as they are managed carefully.
Ok, that’s FIV - what about FeLV? How does it differ?
Feline Leukaemia virus is a retroviral infection caused by infection with the FeLV gamma-retrovirus. It’s spread mainly through prolonged close contact, grooming, sharing water or food bowls, from infected queens to kittens, and via fighting or social contact between household cats.
Resistance to infection increases with age, and kittens have the highest chance of becoming progressively infected.
Progressively infected cats shed the virus in saliva, nasal secretions, urine, faeces and milk. The new host picks up the virus, and after this, the patient may or may not become persistently infected, depending on their immune system. Patients are known as progressively infected if they do not have sufficient immunity to clear the virus, regressively infected if their immune system manages to contain the virus and prevent it from replicating excessively, and abortively infected if they have sufficient antibodies to clear the virus from the system completely.
Progressively infected patients shed an infectious form of the virus, which, when ingested by a susceptible host, spreads from the local lymph nodes to lymphocytes and then ultimately to the bone marrow. Here, FeLV-containing platelets and white blood cells are produced and released into the bloodstream, making the virus detectable on antigen testing.
So what happens when our cat becomes progressively infected with FeLV?
Since FeLV affects the bone marrow, we see significant disease, including bone marrow suppression, anaemia, and neoplasia. Unfortunately, FeLV is more aggressive, often life-limiting, and more easily spread through close contact than FIV, resulting in a poorer prognosis for infected patients.
Regressively infected cats can become reactivated and develop FeLV-associated diseases, such as anaemia or bone marrow suppression, particularly if they become immunocompromised or unwell.
Okay, so that’s what FeLV and FIV are, but how do they impact our patients?
FIV-positive cats often live relatively normal lives for years.
In fact, the most significant risk to these patients comes from their compromised immune system, making them more likely to present with:
Chronic dental disease, such as feline gingivostomatitis-pharyngitis complex (FCGS), where the immune system does not react normally to bacteria within the mouth, causing oral ulceration and pain
Delayed healing of skin wounds or abscesses
Recurrent skin infections
Chronic rhinitis or conjunctivitis
Generalised lymphadenopathy.
A classic example of a FIV-positive cat is the big old stray tomcat brought in with an abscess. He’s entire, has a big ol’ chunky entire cat face, is covered in scars, and then on bloods, he tests positive for FIV.
However, not every patient is like that - those well-cared-for indoor cats who test positive on routine screening (but appear fine) are also common. In fact, these cats can do really well with good care.
Unfortunately, cats with FeLV have a poorer overall prognosis.
Many progressively infected cats develop:
Anaemia due to bone marrow suppression
Lymphoma, especially mediastinal lymphoma in younger cats
Immunosuppression, so they’re prone to chronic infections, like our FIV-positive cats
Reproductive issues (if breeding isn’t controlled)
Neurological signs in some cases
Sadly, FeLV is one of the leading infectious causes of death in young cats.
What clinical signs should we look out for in FeLV/FIV patients?
Most cats won’t present with specific signs of FeLV or FIV. Instead, they’ll come in with things like:
Weight loss
Poor body condition
Chronic oral pain (salivating, dropping food, chewing on one side, inappetence/anorexia, gingivitis)
Chronic nasal discharge or sneezing
Non-healing wounds
Repeated abscesses
Persistently enlarged lymph nodes
Pyrexia
Anaemia (lethargy, pallor, exercise intolerance, etc.)
What about diagnosing these patients - how do we do it accurately?!
Accurately confirming a FeLV or FIV infection isn’t always easy. No test is perfect, and false positives can happen, so a patient should NEVER be euthanised based on a positive test result.
We perform several different tests, either as a first-line test or to confirm a suspicious result. These include antibody and antigen testing, Western blot testing, and PCR testing. It’s vital that, as nurses, we know which test is performed when and what the limitations are for each method.
First-line tests
The go-to in practice test is the rapid patient-side screening test. This test detects FeLV antigen (specifically, the FeLV p27 antigen, a major structural protein within the virus) and FIV antibodies in the blood.
There are several types of screening tests commonly used in practice, including the Idexx SNAP Combo test, the Witness test, and the SpeedDuo test. These are all simple to use and provide results quickly, but they’re not perfect and false positives can happen.
How to interpret your patient’s results
A positive FeLV ‘snap’ test in a sick cat suggests the patient is actively infected and has circulating FeLV virus.
If you’re testing a healthy patient and they are FeLV-positive, it doesn’t necessarily mean they have an active infection. It could be a transient case - many healthy cats can actually clear the virus and may not test positive in the future. Because of this, we recommend double-checking 12 weeks later, ideally using a different testing method, to confirm the result.
Though rare, false-negative FeLV results are also possible. This can be observed in patients with regressive FeLV, where the infection is present in the bone marrow but not in the bloodstream.
If there’s any doubt in your ‘snap’ test result, confirm with a PCR (polymerase chain reaction) test, which looks for viral DNA within blood or bone marrow, depending on the sample collected.
A positive FIV ‘snap’ test suggests that a patient has been exposed to FIV, mounted an immune response, and created antibodies against the virus as a result. Again, false positives can occur, particularly in younger cats (<6 months old) who may have maternally derived antibodies. Repeat testing is recommended, ideally using either PCR, Western blot, or virus isolation testing methods.
Some areas (eg, Australia, Asia) vaccinate against FIV; in these cases, false-positive results may be seen in healthy vaccinated cats.
When should we test?
Any unwell cat with suspicious signs (eg, anaemia, neoplasia, recurrent infection) should be tested to identify clinical disease causing their clinical signs. Aside from this, testing for infection control, rehoming and management decisions is recommended in:
Stray cats, particularly those with bite wounds or evidence of fighting
Entire males in multi-cat households
New intakes at rescue centres
Kittens with a FeLV-positive queen
What other tests might we perform?
We’ve chatted a lot about testing for FeLV/FIV specifically, but if you’ve got a sick patient, that’s not all you’ll be testing for.
We’ll likely need generalised bloodwork (haematology and biochemistry) and potentially urine analysis and diagnostic imaging to investigate their clinical signs further, look for contributing infection or diagnose concurrent diseases like neoplasia. In severe cases (more so with FeLV than FIV), we may also need to perform bone marrow sampling.
Ok, so your patient has FeLV or FIV. What now?!
The bad news? There’s no cure, but there’s still plenty we can do to help these patients.
Neither FeLV nor FIV has a cure, but good nursing, careful preventative healthcare, supportive treatment, and proactive management can significantly extend and improve the quality of life.
This care includes:
Prompt and aggressive management of secondary infections with antibiotics used appropriately where needed
Providing high-quality nutrition both in and out of the hospital, to ensure these patients meet their calorie needs and maintain their body condition.
Maintaining dental hygiene, since FIV-positive cats often need multiple dentals due to gingivostomatitis
Maintaining a stress-free home environment, particularly within multi-cat household settings. Keeping infected cats indoors, in stable social groups with no fighting, is essential.
Chemotherapy administration (under vet direction) in FeLV-positive cats with neoplasia, or transfusion administration and monitoring in those with anaemia, though, due to their poor prognosis, many cats are sadly euthanised at this stage.
One final small point (okay, soapbox moment…) from me on inpatient care for these individuals - please don’t put them in isolation unless absolutely necessary. They’re immunocompromised and they’re far more likely to pick up an infection in hospital than spread one - yes, barrier nurse them and follow good hygiene protocols, but bear in mind that it’s as much for their protection as it is for your other patients.
What about client support and long-term advice?
As nurses and technicians, providing client support and advice is a huge part of our role.
There’s also still quite a bit of misinformation out there about how to manage FeLV/FIV patients, and sadly, stray cats are still, at times, euthanised based on a positive test result when there are suitable homes out there for them. So let’s look at the current recommendations when it comes to FeLV and FIV - so you can advise your clients accordingly.
First, let’s discuss ways to prevent the spread of disease.
FeLV-positive cats should live indoors and either alone or with other FeLV-positive cats only. If the home has both FeLV-negative and positive cats, they should be segregated, since the disease spreads through friendly contact.
FIV-positive cats should be kept indoors only and neutered to prevent roaming and fighting. They can live in multicat households with FIV-negative cats, provided that the group have a strong social structure and there is no conflict.
Next up - vaccination and preventative care (and not just for positive cats, either).
FeLV vaccination is not a core vaccine, but is strongly recommended for at-risk cats, including those with outdoor access, in multi-cat households where one or more cats have outdoor access, and for kittens.
FIV vaccination exists in some countries, but it isn’t routine. Its effectiveness is limited, and many countries have discontinued its use because vaccinated cats can still test positive for antibodies.
Additionally, in FeLV/FIV-positive cats, general preventive care is also essential. These patients are immunocompromised; they can’t afford to contract other diseases, parasite infestations, or other infections. Talk to clients about raw feeding (or, more specifically, NOT raw feeding), regular health checks (ideally every 6 months), annual vaccination, and more. These are great patients to see regularly in nurse clinics, just to ensure everything is okay, and to intervene early if not.
And lastly, let’s talk about HOW to support your clients.
A new FeLV or FIV diagnosis is often scary and can feel like a death sentence, but it doesn’t have to be. Make sure your clients know that many of these patients can live happy lives for many years, just with some extra care taken over their health.
Discuss the lifestyle changes we’ve mentioned, and provide advice on transitioning cats to an indoor-only environment, enriching their space to prevent frustration and boredom, and how to keep the home stress-free.
Talk about retesting (if needed) and when it would be appropriate to do this (though this will often be covered for you by your vet when discussing the patient’s diagnosis).
Lastly, discuss the importance of neutering, vaccination, and ongoing preventive care. Often, these things are seen as ‘nice-to-haves,’ but for these immunocompromised patients, they are truly essential.
So, there you have it: the essential information, myths and misconceptions, and nursing considerations behind FeLV and FIV. Let’s recap what we’ve discussed today:
They’re not the same - FeLV spreads through close contact and causes anaemia, neoplasia and bone marrow suppression, while FIV spreads through fighting and causes progressive immunocompromise.
Testing is not 100% accurate in every case, so it is essential to understand your testing methods, limitations, and when to repeat a test to rule out a false positive.
There’s no cure, but that doesn’t mean there’s nothing we can do. Focus on keeping the patient happy, healthy, stress-free, and comfortable for as long as possible, and support your clients while they do so at home.
Did you enjoy this episode? If so, I’d love to hear what you think. Take a screenshot and tag me on Instagram (@vetinternalmedicinenursing) so I can give you a shout-out and share it with a colleague who’d find it helpful!
Thanks for learning with me this week, and I’ll see you next time!
References and Further Reading
Barrs, V.R. and Beatty, J.A., 2012. Feline immunodeficiency virus (FIV) infection: an overview. Australian Veterinary Practitioner, 42(1), pp.18–27.
European Advisory Board on Cat Diseases. 2017. ABCD Guideline for feline immunodeficiency virus [Online]. Available from: https://www.abcdcatsvets.org/guideline-for-feline-immunodeficiency-virus/
European Advisory Board on Cat Diseases. 2025. ABCD Guideline for feline leukaemia virus infection [Online]. Available from: https://www.abcdcatsvets.org/guideline-for-feline-leukaemia-virus-infection/
European Advisory Board on Cat Diseases. 2020. ABCD FIV diagnostic tool [Online]. Available from: https://www.abcdcatsvets.org/wp-content/uploads/2022/11/TOOL_FIV_Feline-immunodeficiency-virus_July_2020_EN.pdf
Hartmann, K., 2012. Clinical aspects of feline retroviruses: a review. Viruses, 4(11), pp.2684–2710.
Hosie, M.J., Addie, D., Belák, S., Boucraut-Baralon, C., Egberink, H., Frymus, T., Gruffydd-Jones, T., Hartmann, K., Lloret, A., Lutz, H., Marsilio, F., Pennisi, M.G., Radford, A.D., Thiry, E. and Truyen, U., 2009. Feline immunodeficiency. ABC of Feline Infectious Diseases, Journal of Feline Medicine and Surgery, 11(7), pp.575–584.
Little, S., 2010. Feline leukemia virus and feline immunodeficiency virus. Top Companion Animal Medicine, 25(4), pp.189–198.
Little, S., Levy, J., Hartmann, K., et al. 2020. Updates to the AAFP Feline Retrovirus Testing and Management Guidelines. Journal of Feline Medicine and Surgery, 22(1), pp.5–30.
Levy, J.K., Crawford, C., Hartmann, K., Hofmann-Lehmann, R., Little, S., Sundahl, E. and Thayer, V., 2008. 2008 American Association of Feline Practitioners’ feline retrovirus management guidelines. Journal of Feline Medicine and Surgery, 10(3), pp.300–316.
Ueland, K. and Lutz, H., 2020. Feline leukemia virus (FeLV). In: S.J. Ettinger, E.C. Feldman and E. Côté, eds. Textbook of Veterinary Internal Medicine. 9th ed. St. Louis, MO: Elsevier.
