Feline leukemia (FeLV)

What feline leukemia is

The name frightens people, and it misleads them. Feline leukemia is a viral infection, not a cancer. The test we run looks for a protein the virus makes in your cat's blood, not for cancer cells. Most cats who test positive will never develop leukemia at all. The virus can cause blood cancers, and we come back to that without flinching, but a positive result is not a cancer diagnosis.

And right away, the most important thing: this is not FIV. Both viruses are picked up by the same small test, so they get named together almost every time. They are two different diseases with two different outlooks. FIV is a lentivirus that slowly wears down immune defenses over years. Feline leukemia is a gammaretrovirus that attacks the marrow that makes blood, and it causes blood cancers. If someone has reassured you about FIV, or if you have read somewhere that positive cats live happy years, do not carry that relief across. The prognosis, said plainly tells you how it actually stands, and on what sources.

What the virus is. FeLV, for feline leukemia virus, is a retrovirus. A retrovirus does not merely circulate through the body: it writes its own genetic material into the DNA of your cat's cells. That is why, once it is truly established, it is not cleared. This is not about the strength of the immune system or the quality of the care. It is mechanics.

It gets in through the mouth and the nose, where a cat has the most contact with other cats' saliva. From there it reaches the local lymphoid tissue, and from there, the bone marrow.

The bone marrow is the heart of the problem. It is the factory that makes blood: the red cells that carry oxygen, the white cells that fight infection, the platelets that stop bleeding. When FeLV settles into that factory, several of those lines can fall at once. That is the sharpest line between this virus and FIV, and it is measured: in a study of 3,780 owned cats, cats positive for FeLV had markedly higher odds of anemia, low platelets and low white cells, which was not the case in FIV-positive cats (Gleich and Hartmann, J Vet Intern Med 2009).

Three things you should know right now, and that nobody may tell you.

• You cannot catch this from your cat. No human being has ever been found to carry FeLV, and no case of human leukemia has ever been traced to this virus, despite research done specifically to look for it (Nowotny et al., Lancet 1995, cited by the ABCD). Hold him, let him sleep on your bed, share your days with him. So can your children.
• The dog in the house is not at risk. There has never been a reported case of natural transmission of FeLV to a non-cat species (ABCD, Guideline for Feline Leukaemia Virus Infection, updated 2025). This is a cat virus.
• It does not travel through the air. Unlike panleukopenia or the upper respiratory viruses, it does not spread by simply being nearby and it does not cross a room. It requires direct contact between two cats (AAFP 2020). That is a real constraint on your household, but it is also what makes prevention concrete and doable.

To understand how the test works, when it becomes reliable and why we repeat it, see Feline viral screening. This page picks up where that one leaves off.

What happens after a cat meets the virus

Before anyone talks about prognosis, you need the vocabulary. A cat who meets FeLV does not automatically become a sick cat. Several different things can happen, and the word written on your cat's report governs everything else on this page. This is the most technical section, and it is the one that makes all the others readable.

• Abortive infection. The immune system beats the virus back before it establishes itself. Nothing of the virus is left behind: no viral protein, no RNA, no DNA written into the cells. The only trace that this cat ever met FeLV is his antibodies. Of all the outcomes, this is the best one (Hofmann-Lehmann and Hartmann, J Feline Med Surg 2020). One honest qualification: in Quebec we do not look for this outcome in routine practice, because the antibody test it requires is not run routinely.
• Regressive infection. The immune system regains the upper hand without eliminating the virus. The cat stops shedding infectious virus, and he no longer passes it to his feline housemates through saliva, bowls or the litter box (AAFP 2020). But the virus stays written into his DNA as provirus, and it can wake up, sometimes years later, especially if he becomes seriously ill or receives treatment that lowers his defenses. This is the contained form. It is not a cure.
• Progressive infection. The cat does not contain the virus. It replicates, settles into the bone marrow, then reaches the mucosal and glandular surfaces: the cat then sheds virus continuously, mostly in saliva. This is the severe form, the one that produces most of the illness and most of the deaths associated with FeLV (Hofmann-Lehmann and Hartmann 2020). It is also the form the prognosis section is about. We will not dress it up as anything else.
• Focal infection. Uncommon, and worth naming because it explains situations that otherwise look like nonsense. The virus stays walled off in a single tissue: the spleen, a lymph node, the intestine, the mammary glands. Tests then become unstable, positive at one moment and negative at another. One documented case: a queen whose virus was sequestered in her mammary glands passed FeLV to her kittens in her milk while her blood test was negative (Hofmann-Lehmann and Hartmann 2020).

The older words you will meet online. The literature of twenty years ago used a different vocabulary, and it is still everywhere on the internet. The mapping is direct: persistent viremia means progressive infection, and latent infection means regressive infection (AAFP 2020). The old vocabulary was not so much wrong as imprecise, and it carried an implication we now know is false: that a cat could clear this virus completely.

It is decided over the three to four months after contact. The European guidelines place the decision in the first twelve weeks; the North American guidelines write that a cat initially positive on both tests can shift to a regressive pattern, usually within sixteen weeks of infection (ABCD 2025; AAFP 2020). That is why one result never closes the file, and why we will not give you a prognosis at the first visit.

And the balance is not fixed for life. A cat with regressive infection can see the virus wake up years later, on the back of a serious illness or a treatment that lowers his defenses.

One thing we will not hand you: percentages. You will read elsewhere that such and such a share of cats ends up in one form or another. Those numbers exist, but they swing enormously from one setting to another. Measured with the same full method in four European countries, the rates of progressive infection varied widely between countries (Giselbrecht et al., Viruses 2023). These are not biological constants: they depend on cat density, on how common the virus is locally, and on age at the time of contact. Publishing a set of percentages would give a false impression of precision, and we would rather not.

How the virus passes from cat to cat

Saliva, above all. A cat with progressive infection sheds massive quantities of virus in his saliva, continuously (ABCD 2025). That is the main route, and it explains everything else.

One received idea has to go right away. For a long time FeLV was called the friendly cats' virus and FIV the fighters' virus. That is no longer defensible. The European guidelines place fighting and biting on one hand, and social behavior on the other, at the same rank as the most effective means of transmission: mutual grooming, shared food and water bowls, a shared litter box (ABCD 2025). Two cats who groom each other affectionately pass the virus just as well as two cats who fight.

In practical terms, the routes that matter in a home are these:

• Mutual grooming. The most effective of all, and the hardest to prevent between two cats who like each other.
• A shared water bowl and a shared food bowl. A genuine route of transmission, not a theoretical precaution, for the reason set out below.
• A shared litter box. Experimental exposure to feces alone produced only abortive infections (ABCD 2025), so the litter box counts for less than saliva. It still raises the infection pressure in the house.
• Bites. In fights, or between cats of the same household.

From queen to kittens. A carrier queen passes the virus during pregnancy, by grooming her kittens after birth, and in her milk (ABCD 2025). It is common inside a litter born to a carrier mother. Important point: not every kitten in an exposed litter is infected. Every kitten has to be tested individually. We never test one kitten as a stand-in for his brothers and sisters (AAFP 2020).

By blood transfusion, including from a cat whose rapid test is negative. The viral DNA written into the cells of a cat with regressive infection is itself infectious. Ten cats transfused with blood from aviremic provirus carriers all developed active infection, and four of them a lymphoma (Nesina et al., Retrovirology 2015). That is a fact to know about your cat, not just a laboratory curiosity: a carrier, progressive or regressive, can never be a blood donor. We come back to it in Living with a positive cat.

A carrier in perfect health is as contagious as a sick one. The concentration of virus in the saliva and blood of a healthy-looking cat with progressive infection is as high as in a cat showing signs of disease (ABCD 2025). How well he looks tells you nothing about the risk he poses to other cats. It is counter-intuitive, and it matters for what follows.

The virus outside the cat: fragile, but not harmless. FeLV is an enveloped virus, quickly destroyed by detergents, ordinary soap and routine disinfectants (AAFP 2020). Do not conclude from that that a shared bowl is safe, because how fragile the virus is depends heavily on conditions. On a dry surface, meaningful quantities of virus are still present through the first 30 to 60 minutes, which the guidelines judge enough to infect another cat through a shared food or water bowl. In a moist setting it lasts far longer: infectivity drops only minimally even after 48 hours, and standing water in a shared bowl is exactly that kind of setting (ABCD 2025, citing Francis et al. 1979).

And a piece of good news people forget to give you. If a carrier leaves the house, no waiting period is needed before bringing another cat in. A thorough cleaning of contact surfaces is enough, bowls and water dishes included; lasting contamination of surfaces is not considered a risk (ABCD 2025; AAFP 2020). You do not have to disinfect the house from top to bottom or throw out furniture. If you are at that stage, see Introducing a new cat.

Which cats are actually at risk, and what the vaccine does

Age at the moment of contact changes almost everything. In the experimental work that still serves as the reference, every newborn kitten and most cats up to two months old that were exposed went on to develop permanent infection, against a small minority of cats exposed at four months or older (Hoover et al., J Natl Cancer Inst 1976, as reported in the AAFP guidelines 2008). This is 1970s work with a controlled dose, and we cite it for what it demonstrates: a kitten does not have an adult cat's defenses.

But age-related resistance is not immunity. An adult cat can be infected. And here is the part that surprises everyone: when you test a population, it is the adults who most often come back positive, not the kittens. Across North America, 3.3 percent in adults against 1.4 percent in juveniles, over 18,038 cats in the United States and Canada (AAFP 2020, citing Levy et al. 2006). The reason is not mysterious: the risk of running into a carrier accumulates year after year. Feline leukemia is not a kitten disease. Kittens are simply far worse at surviving contact with it.

The cats genuinely at risk:

• The cat who goes outdoors, even a little, even just into the yard.
• The unneutered male, who roams and fights.
• The cat living in a large household with no testing, or coming from a shelter or a hoarding situation without adequate testing.
• The kitten born to a carrier queen.
• The unvaccinated cat.
• The cat brought in for a fight wound. Among cats presented to clinics for an abscess or a bite, more than 8 percent carried FeLV, well above the proportion in healthy cats (Goldkamp et al., J Am Vet Med Assoc 2008).

To place the order of magnitude. Roughly 3 cats in 100 tested across North America carry FeLV antigen, based on 62,301 cats in clinics and shelters in the United States and Canada (Burling et al., J Am Vet Med Assoc 2017). Those are cats presented and tested, not a random sample of all cats: read it as an order of magnitude, not as a population rate. Among sick cats, the proportion climbs sharply.

The vaccine: what it does, and what it does not. We follow the North American guidelines: the feline leukemia vaccine is recommended for every kitten under one year of age, whatever lifestyle is planned, and after that on a risk assessment in the adult (2020 AAHA/AAFP Feline Vaccination Guidelines, J Am Anim Hosp Assoc 2020). The reason to vaccinate every kitten is simple: from his first weeks of life, nobody knows what life that cat will end up having, and that is precisely the age at which exposure does the most damage. This page does not publish an adult booster interval: that is a conversation to have with us, starting from your cat's real exposure.

We test before we vaccinate. Always. Vaccinating a cat who already carries the virus gives him nothing: two commercial vaccines given repeatedly to infected cats changed neither the quantity of virus, nor the antibodies, nor life expectancy (Helfer-Hungerbuehler et al., Vaccine 2015). And it would cost us the single most important piece of information about his health. For the same reason, screening is planned as a matter of course when we spay or neuter a cat, male or female: we want to know his status before he goes under, and that is often where it is found.

The vaccine is not an absolute shield, and we will not sell it to you as one. It effectively prevents progressive infection, the form that makes cats sick and shortens their lives. But several current vaccines do not consistently prevent the virus from writing itself into the DNA after exposure, and the guidelines conclude that it cannot be said that vaccination protects against all outcomes of the infection (AAFP 2020). The WSAVA says the same in fewer words: no FeLV vaccine is perfect (Squires et al., J Small Anim Pract 2024). It is real and important protection. It is not a guarantee, and it never replaces testing or separation.

For your cat's schedule and the conversation about real risk, see cat vaccination. If you have just brought home a kitten, see also Welcoming a kitten.

What a positive result changes

This page does not re-explain how the test works. That lives on Feline viral screening, with the method and when we repeat it. What concerns us here is narrower: what a positive means, and why we never stop there.

One positive rapid test is not a diagnosis. This is not excessive caution, it is arithmetic. When a disease is uncommon in the population being tested, a large share of the positives that come back are false. The guidelines write it plainly: in a population with low prevalence, under 0.5 percent for example, more than half the cats that test positive are likely to be uninfected (AAFP 2020, citing Jacobson 1991). And it is not theoretical: of 801 cats referred to an adoption program as FeLV positive, close to one in five turned out not to be infected (Lockhart et al., J Feline Med Surg 2020).

The reverse is true too, for exactly the same reason: a negative result is solid. The value of a negative is far higher than that of a positive, precisely because the virus is uncommon here (Hofmann-Lehmann and Hartmann 2020). The one thing that undermines a negative is timing: a test run too soon after a possible exposure can miss an infection that is not yet detectable. That window lives on the screening page.

An honest exception. In a cat who is already sick, with signs that fit FeLV, a first positive result is far more reliable: that cat already belongs to a high-risk group, and a false positive is less likely there (Hofmann-Lehmann and Hartmann 2020). In that situation we move faster. Put plainly: if your cat was screened while he was well and came back positive, hold your reaction until we confirm. If he was tested because he was ill, we will not wait.

Results that contradict each other are not a laboratory error. Each test looks at a different moment and a different part of the infection, and regressive infections sit at low levels where one test can fall under the limit of detection while the other does not.

An Ontario study documented this strikingly. Across 1,692 records, 73 cats were antigen positive; 21 of them, close to one in three, were negative on the search for viral DNA. Eighteen of those 21 cats in fact had immune-mediated bone marrow disease. Seven were retested once their real disease was under control: all had come back negative. The authors conclude that it is unlikely either test was wrong, and that it is the clinical interpretation that has to adjust (Kornya, Bienzle and Beeler-Marfisi, J Feline Med Surg 2023). That is the Canadian data closest to you.

Classifying a cat takes two things. The search for viral antigen in the blood, and the search for viral DNA written into the cells. One without the other is not enough: the DNA test detects cats with progressive infection and cats with regressive infection identically, and so has limited value without the antigen result beside it (AAFP 2020; Westman et al., Aust Vet J 2025). It also often takes two points in time, because the classification can change in the first months. Until that classification is done we will not give you a prognosis, and not out of caution for its own sake: the two answers describe two different lives.

Here is the actual gesture. The rapid test, the one that gives the first answer, is run here, in our own in-house laboratory. When it comes back positive we do not run it again hoping for a different answer: a blood draw goes to the laboratory, which takes the search further than a rapid test can. Your veterinarian will tell you exactly what was requested, and when.

The laboratory can measure how much virus is there, and that number carries the prognosis. This is the most useful thing in this section. In a cohort of 127 positive cats followed for eight years, the cats with a high viral load and the cats with a low load had radically different futures: in the high-load group almost none were still alive at the end of the follow-up, while most of the low-load group were, and that second group had not even reached its median survival (Beall et al., J Feline Med Surg 2025; thresholds established in Beall et al., Viruses 2021). One reservation to know: some authors of that work are employed by the manufacturer of the tests being evaluated.

That is why a positive or a negative does not sum up everything a laboratory can say about a result, and why it is worth asking your veterinarian what was measured. See our laboratory service.

The prognosis, said plainly

This section is the heart of the page. We are going to start with the hard part, because you deserve to have it first rather than after three paragraphs of softening.

One. Feline leukemia does not carry the prognosis of FIV. It has been measured, in a single population and with the same methods. In a British sanctuary cohort followed for twenty years, FIV-positive cats lost a modest part of their life expectancy compared with uninfected cats. Cats positive for feline leukemia lost an enormous part of it, on a completely different scale (Castillo-Aliaga et al., Vet Rec 2026). The authors themselves flag that some of their groups were small, and we tell you so too. The direction turns up elsewhere: in an Italian veterinary clientele, measured survival in FeLV-positive cats was far shorter than in age-matched uninfected cats, while FIV status did not significantly affect longevity there (Spada et al., Prev Vet Med 2018). We do not print the gap as a number here, because a gap drawn from one population does not transfer to your cat.

If you arrived on this page with the idea that positive cats live happy years, that is a true sentence about FIV. It does not carry across. We would rather tell you today than let you find out in eighteen months.

Two. For a confirmed progressive infection, the range. Most studies report roughly one to three years after a confirmed diagnosis of progressive infection, and very few cats reach eight years. The guidelines summarize the same thing differently: these cats typically succumb within a few years (AAFP 2020). That is the only range this page publishes, and it describes groups of cats, not yours.

Three. The spread between studies is mostly about the cat at diagnosis, not luck. This matters to you, because it means the darkest figures often describe a population that is not yours. In a Brazilian hospital cohort where the great majority of cats were already sick when they were tested, being sick at entry raised the risk of death sharply, and the authors themselves explain that their result is far darker than in countries where healthy cats are screened (Biezus et al., PLoS One 2025). A cat screened while he was well is not in the same situation as a cat tested because he had collapsed. One measured factor counts particularly: a low red cell count at diagnosis is associated with shorter survival, and it is one of the reasons we run a complete blood count from the start (Spada et al. 2018).

Four. Viral load splits one positive result into two futures. We said it in the previous section and it bears repeating here: two equally positive cats can have completely different prospects depending on how much virus is measured. That is why we will not give you a prognosis on the strength of one positive result. What counts, after a confirmation, is not a yes or a no: it is knowing where your cat sits on that spectrum, and that is a question to put to your veterinarian.

Five, and only now. A positive result is never by itself a reason to euthanize a cat. The North American guidelines write that a diagnosis of retroviral infection should never be the sole criterion for euthanasia (AAFP 2020); the 2025 Australian and New Zealand guidelines go further still: cats with progressive infection should not be euthanized on the basis of a positive diagnosis, since some remain healthy for years (Westman et al., Aust Vet J 2025). History argues for that caution: in the old test-and-remove campaigns, cats who were never infected at all were euthanized for nothing. And adoption remains a real and common outcome: in a dedicated adoption program, most of the confirmed positive cats found homes (Lockhart et al. 2020).

That sentence is true. It does not contradict the four points before it, and we are not placing it here to erase them. The two go together: this virus shortens life, and a test result is not a verdict. That is exactly how we will talk about it with you in the room.

Six. A cat with regressive infection is a different conversation. His life expectancy comes close to that of an uninfected cat: in the Brazilian cohort, regressive infection did not shift the survival curve (AAFP 2020; Biezus et al., PLoS One 2025). That is genuinely good news and we will say so. It applies only to regressive infection: nothing in this paragraph changes what is written above about progressive infection.

It is not a clean bill of health either. Two reservations we would rather name. An association between regressive infection and lymphoma has been observed in some countries, Canada among them, over a twenty-year span, while other work concludes that life expectancy is similar to that of an uninfected cat: the question is not settled (Westman et al. 2025). And the sleeping virus can wake up, especially if the cat becomes seriously ill or receives a treatment that lowers his defenses. That is why we do not close the file: we watch it over time, and when the next test is due is decided at the visit, with your veterinarian.

A word about the very dark numbers you will find online. Frightening two-year and three-year mortality figures still circulate everywhere. They come from crowded multi-cat households studied before modern care, before FeLV vaccination, and before anyone distinguished progressive from regressive infection. The reference review that carries them says in the same sentence that mortality is much lower today, at least for cats who are well cared for and kept strictly indoors (Hartmann, Viruses 2012). Do not read them as a forecast for your cat, and do not repeat them as though they were current.

When the question becomes comfort rather than duration, the quality-of-life tool and End-of-life care are there. You will not have to improvise.

What the virus causes, and what can be treated

Anemia first, because it is the most common and because it is the one that most often changes what we do next. Anemia is a shortage of red blood cells. It is the most common non-tumor complication of FeLV: in a large European study comparing sick cats with each other, FeLV-positive cats were close to ten times more often anemic than sick uninfected cats (Studer et al., Viruses 2019). Among positive cats sick enough to be referred to a specialist, 71 percent were anemic, and three-quarters of those anemias were of the kind the marrow does not repair (Pare, Ellis and Juette, PLoS One 2022): that is a referral population, not the picture of a cat screened while healthy.

Most often it is of the kind the marrow does not repair: only about one FeLV-associated anemia in ten regenerates (Hartmann, Viruses 2012). In other words, it does not correct itself.

And here is the point that really counts: it is multifactorial. The anemia of a positive cat can come from direct injury to the marrow, but also from chronic inflammation, from destruction of red cells by the immune system, from bleeding on the back of a platelet drop, or from a blood parasite such as hemotropic mycoplasma (Hartmann 2012). Several of those causes treat well. A blood parasite that a healthy cat would barely notice can cause severe anemia in a positive cat, and it responds to an antibiotic.

That is why we look further than a positive test. A positive cat who becomes anemic is not a closed file, it is a file to open: we look at his blood under the microscope, we look for a blood parasite, we look for red cells being destroyed by the immune system, and we look at the platelets too. See our laboratory service.

Several blood lines falling together: what really separates FeLV from FIV. The virus does not only drop the red cells. Platelets and white cells fall too, often at the same time. Across 3,780 owned cats, FeLV-positive cats had markedly higher odds of anemia, low platelets and low white cells; the authors conclude that blood abnormalities are common in FeLV-positive cats and not in FIV-positive cats (Gleich and Hartmann 2009). One nuance, because it is in the same study: FIV-positive cats were also more often low on certain white cells. What characterizes FeLV is dropping several lines at once.

In practical terms, for you: a platelet drop shows up as bleeding that appears without an injury. It was present in 52 percent of the positive cats in a referral series (Pare et al. 2022). That is in the red flags at the top of this page, and it is same-day.

Blood cancers. Lymphoma leads. In the twenty-year British cohort, 76.9 percent of the tumors associated with the virus were lymphomas (Castillo-Aliaga et al. 2026), and the causal link between the virus and tumor development is established in a way it is not for FIV (Westman et al. 2025). The virus also causes leukemias proper and other marrow diseases, more rarely.

Two qualifiers, pulling in both directions. The first runs against intuition: FeLV causes lymphomas, but today the great majority of feline lymphomas occur in negative cats. In the United States, around 70 percent of feline lymphomas were attributed to FeLV in the 1970s, against under 15 percent in the two decades before 2003 (Louwerens et al., J Vet Intern Med 2005). The message is about the share attributable to the virus, not about how often lymphoma happens. The disease itself is covered on Lymphoma in cats.

The second: a lymphoma in a positive cat is not a foregone conclusion, and giving up without discussing it is not justified. The Australian and New Zealand guidelines consider chemotherapy justified provided it translates into better quality of life for the cat, and FeLV-positive cats with a lymphoma in the chest have responded to a chemotherapy protocol (Westman et al. 2025). Careful not to over-read it: that series had no negative comparison group, so it does not show that FeLV status has no effect on prognosis.

The chest form, the one behind the breathing red flag. In a series of cats with a lymphoma in the chest, difficult breathing was the presenting complaint in 78 percent of them and half had fluid around the lungs, in cats with a median age of three years (Fabrizio et al., J Feline Med Surg 2014). Note what the same series also shows: only a small minority of those cats were FeLV positive. In the chest, radiographs lead, and fluid that is making breathing hard can be tapped and drained here during our opening hours. Looking at the chest with ultrasound, beyond the heart, is a separate appointment that is planned with a visiting specialized imaging team. See our imaging service.

The mouth. Inflammation of the gums and the mouth is one of the three signs that stand out clearly when sick positive cats are compared with sick negative cats, along with anemia and loss of appetite (Studer et al. 2019). A cat who drools, who turns away from dry food or whose gums are red is in pain. And we will be straight with you: in FeLV-positive cats, the response to dental extractions is significantly poorer than in other cats (Silva et al., Animals 2021, a small retrospective series). Poorer is not the same as none: for severe inflammation of the mouth, removing the affected teeth with all their roots remains what gives the best long-term outcome in a retrovirus-positive cat (AAFP 2020). Affected teeth are removed here, sometimes one, sometimes several, sometimes all of them. So the poorer response does not mean nothing should be done: it means waiting costs more here than elsewhere.

A severe gut crisis. Some positive cats develop a brutal episode: bloody diarrhea, vomiting, complete refusal to eat, with a collapse of the white cells that defend the intestine (Hartmann 2012). This is an emergency, because the cat dehydrates fast at exactly the moment his defenses are at their lowest. If your cat stops eating and there is no blood and no fever, see also My cat has stopped eating; but with a positive cat, call rather than watch.

The spinal cord, rarely. The virus can reach the spinal cord directly: unusual vocalizing, a cat very sensitive to touch, then progressive weakness of the back legs. A series of sixteen cats documented that course (Carmichael, Bienzle and McDonnell, Vet Pathol 2002). It is rare. Far more often, when a positive cat loses the use of his back legs, it is a lymphoma compressing the cord (Hartmann 2012). In both cases it is same-day: every hour counts for recovery.

And the principle that governs all of the above. A positive cat also catches everything other cats catch. The guidelines are explicit: diseases that would be considered likely, or even merely possible, in an uninfected cat must be ruled out by a full workup before a problem is attributed to the virus (Westman et al. 2025). Blaming every symptom on FeLV is the most expensive mistake anyone can make with these cats, because it misses the things that treat.

Give no home medications

Faced with a cat who is in pain, drooling or off his food, the temptation is to give him something in the meantime. Cats are a species apart: their liver does not detoxify like ours, or like a dog's, and several utterly ordinary products kill them. In a cat carrying feline leukemia, whose marrow and defenses are already working against the current, the margin is thinner still. Nothing below is given, for any reason, even once.

Living with a positive cat

Here is what changes starting tomorrow. This section is written mostly for owners of a cat with progressive infection. If your cat has a regressive infection, several instructions loosen, and we say so at every point where that is the case.

Indoors, strictly. This is the first instruction, and it works both ways: your cat does not pass the virus to the cats of the neighborhood, and he is far less exposed to the infections he handles badly. A strictly indoor life prolongs his life and prevents spread (ABCD 2025; AAFP 2020). Secure outdoor access, an enclosure or a closed balcony, is acceptable.

The household question: this is where feline leukemia parts ways with FIV. An FIV-positive cat can often live with negative cats in a peaceful home where nobody fights. For FeLV, the current recommendation is different: a cat with progressive infection should live alone, or with other positive cats (AAFP 2020). The reason is the one from the transmission section: this virus travels through affection as readily as through fighting, and two cats who groom each other share everything.

We owe you an honest note about the strength of that recommendation. The guidelines write it themselves: no recent study has measured the risk of FeLV transmission inside a household. The recommendation follows from the observation that transmission between housemates appears more common for this virus, and from the known route of transmission (AAFP 2020). It is careful expert judgment, not a measured rate. We would rather tell you that than let you believe in a precision that does not exist, and we still think it is right.

Separating means no direct contact: separate rooms, separate bowls, separate litter boxes, no mutual grooming. It is not just a matter of dishes.

A cat with regressive infection sheds no infectious virus under natural conditions and does not pose that risk to his housemates (AAFP 2020). The separation instruction is about progressive infection.

Vaccinate the negative cats in the house: a safety net, never a permit. We vaccinate the other cats in the house even if the carrier is isolated, because isolation protocols eventually give way and a door gets left open one day (AAFP 2020). But we have to be categorical about what that does not do. The European guidelines write that even vaccinated cats are at significant risk in a household under high infection pressure, and that vaccination alone must not be relied on as a protective measure in that situation (ABCD 2025). The vaccine was never designed to absorb daily exposure.

No new cat joins the household while a cat with progressive infection lives there. This is probably the simplest and most important sentence on the whole page (ABCD 2025). If a new cat does join later, Introducing a new cat covers the pace.

If separating is impossible in your home, tell us. We will not lecture you and we will not abandon you. We work with what is workable: more resources for every cat to lower conflict and stress, everyone neutered, everyone indoors, no new cats coming in, testing every cat in the house and repeating it regularly, and vaccination for the negatives (AAFP 2020; ABCD 2025). We will tell you honestly that this is risk reduction, not a guarantee.

Cleaning. Ordinary soap and routine disinfectants are enough: the virus is fragile outside the cat (AAFP 2020). No waiting period is needed before bringing a new cat into a house where a carrier lived, once contact surfaces have been thoroughly cleaned, bowls included (ABCD 2025). You do not need to strip the house or throw out furniture.

Medical follow-up. The guidelines call for a health check every six months rather than once a year, with particular attention to the mouth, the lymph nodes, the eyes and the skin (AAFP 2020). On the laboratory side, the exact wording is careful and we repeat it as it stands: an FeLV-positive cat may need a complete blood count twice a year, and biochemistry and a urinalysis at least once a year (AAFP 2020). The 2025 Australian and New Zealand guidelines are more skeptical still about routine hematology in a cat who is doing well, given the stress of every visit (Westman et al. 2025). Your cat's rhythm is therefore decided with his veterinarian, from his condition and what he tolerates, and not from a calendar written in advance on a web page. What does not change is the reason for looking: anemia is the most common complication of this disease, several of its causes treat well, and it shows in the blood before it shows in the cat. See the health check.

Weigh him, at every visit and at home. Weight, body condition and muscle condition are assessed at every visit, and that is not administrative detail: unexpected weight loss can precede any other clinical sign by months (AAFP 2020). It is often the very first signal, and it is also the cheapest. Weigh your cat at home once a month if you can, on the same scale, and write the number down.

Feeding. A complete and balanced diet, wet or dry, appropriate to his life stage. No raw meat and no raw dairy: the risk of food-borne bacterial and parasitic disease is likely higher in these cats with weakened defenses (AAFP 2020), and the WSAVA Global Nutrition Committee recommends against raw meat-based diets, also for the protection of immunocompromised people in the household. See Raw feeding.

Parasite control is not optional. Controlling internal and external parasites lowers the risk of secondary infection in these cats (AAFP 2020), and it closes the door on the blood parasite that can turn a mild anemia into a severe one. See our pharmacy.

Neuter or spay. It lowers the stress of heat cycles, roaming behavior and fighting, which is to say two of the most important routes of transmission (AAFP 2020). A positive queen should not be bred and should be spayed as soon as her condition allows.

Keep his core vaccines up to date, and do not space them out. This is the instinct people get backwards: a positive cat must not be deprived of his core vaccines on the grounds that he is fragile. He develops more severe forms of panleukopenia and of respiratory infections after natural exposure, and the European guidelines specify that these vaccines should be given regularly even in a strictly indoor cat, which differs from the approach in an FIV-positive cat (Hartmann et al., Viruses 2022; AAFP 2020). The one vaccine we stop is the feline leukemia vaccine itself, which now gives him nothing. The exact rhythm and the choice of products are discussed with us.

Never a blood donor. This is a fact to know about your cat, whichever clinic looks after him: neither a cat with progressive infection nor a cat with regressive infection, even with a negative rapid test, can be a blood donor. The virus written into the cells is still transmissible by transfusion while the antigen test is negative (Nesina et al. 2015; AAFP 2020). This is not an instruction that comes from us: it is a fact about your cat, and it follows him everywhere. It counts most on the day he is taken in by a facility that collects donor blood: tell them his status, and have it written into his record.

Anesthesia and surgery: nothing changes. Being a carrier is not a reason to refuse an anesthetic or to do it differently. Retrovirus-infected cats should receive the same quality of anesthesia, analgesia, surgery and care as any other cat, with the same standard of preoperative assessment (AAFP 2020). And we do not hand out antibiotics around a surgery simply because a chart says FeLV positive.

What exists as treatment, and what does not. There is no cure for feline leukemia. No drug has been shown to make these cats live longer. The most recent guidelines conclude that any drug treatment of FeLV must be considered experimental (Westman et al. 2025). A placebo-controlled trial in 44 naturally infected cats found no significant difference on any clinical or laboratory parameter (Stützer et al., J Feline Med Surg 2013). And let us say it plainly: no antiviral is licensed in Canada for feline leukemia.

Be wary of products sold online. The guidelines warn explicitly about products marketed for FeLV without evidence of efficacy or safety. In the only published series, cats who received one of those products lived less long than the others (Westman et al., Aust Vet J 2024 and 2025). Before you buy anything, call us.

What we treat is the complications, and we treat them early. This is not a consolation prize. Anemia often has a treatable cause, the mouth can be looked after, a secondary infection treats like it would in any other cat. We look for the cause earlier and further rather than blaming everything on the virus. And when a complication goes past what we do here, a lymphoma needing chemotherapy for instance, we refer you rather than giving up, and we keep the follow-up.

The end, said out loud. This cat will probably live less long than you hoped on the day you adopted him. You will have decisions to make, and you will not have to make them alone or improvise them when the moment comes. The quality-of-life tool measures comfort over months, calmly, rather than in the middle of a bad night: you are the one who sees him every day, and that is what makes it work. Bring it to us and we will look at it with you. See also End-of-life care. Come and talk to us before it is necessary; it is easier on everyone that way.

Frequently asked questions

The questions that come up most after a positive result, and the ones owners do not always dare to ask.

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