Feline Leukemia In Your Cat – FeLV+, FLV+
What To Know – What To Do
Ron Hines DVM PhD
Feline leukemia (FeLV) is a common life-threatening diseases of young and middle aged cats. It is caused by a retrovirus . The virus spreads from cat to cat through prolonged close contact or bites from infected cats. It can also be passed from a FeLV-positive mother cat to its kittens. This virus and its distance cousin, feline Immunodeficiency Virus ( FIV) , have the ability to cause a slow, generalized decline in your cat’s health. Of the two, FeLV is the worst. Twenty-five years ago FeLV was considerably more common than it is today. That is because the vaccines your veterinarian has today are better and because veterinarians can now offer you rapid, in-office tests to detect the virus’ presence. (read here)
How Common Is Feline Leukemia?
That is a difficult question to answer. It depends on your cat’s lifestyle. If your cat is allowed to roam, if it received vaccinations against feline leukemia when it was young and the geographic area where your cat lives all come into play. Cornell Veterinary School suggests that 2-3% of all cats in the United States probably carry the virus. However, when cats were presented to them because of signs of illness, the number of FeLV+ cats went up to 30%. A similar sharp upward trend occurred when the cats sampled resided in animal shelters. A Florida sampling set the percentage at 2.3%, with your cat’s age, sex, health status, lifestyle and source being the major determining factors. Adult cats are more likely to be seropositive for FeLV, sexually intact adult males more likely to be positive and outdoor cats that are sick at the time of testing much more likely to be positive than healthy indoor cats. ( read here ) In the UK, the estimate is 1-2% of the island’s cat population. But again, that is highly dependent on which groups of cats are being sampled. In locations where few cats are vaccinated against FeLV, the disease is much more common. There are reports that over 11% of cats tested in Northwestern China carry the virus and almost 25% in Thailand. However, depending on the tests used, those numbers could be inflated by endogenous FeLV virus (replication-defective “provirus” ) that pose no health threat to your cat. I will tell you more about feline leukemia proviruses later.
Feline leukemia is really not a very accurate name for this disease. Less than half of the cats infected with the FeLV virus ever develop leukemia.
When and if they do, it is not actually the FeLV virus that is the cause. It is that your cat’s own cancer-preventing mechanisms have been crippled by the virus’ ability to cause immunosupression – similar to the effects of the human AIDS virus. That immunosupression most often results in lymphomas , not leukemias. ( read here) This same bone marrow suppressive effect is why so many FeLV-positive cats become anemic. (read here)
If My Cat Is Feline Leukemia Positive, What Will Happen?
The majority of cats that are exposed to the Feline Leukemia virus conquer it and recover. Their bodies mount an immune attack against the virus, producing antibodies that cure them or keep the virus at bay (in check) for the rest of their lives. Veterinarians used to believe that within those cat the virus was completely eliminated. We now know that that is not always the case. In some cats the virus continues to lurk in unknown locations – but in a dormant form. Those are called regressive FeLV cases.
When your cat is exposed to the FeLV virus it can react in several ways. Some cats do not become infected due to the dose of virus being too small or due to their vibrant immune system. Certain genes that some cats inherit seem to favor FeLV resistance. Stress at the time of exposure can also give the FeLV virus the upper hand. Others cats develop a latent infection, meaning that their bodies cannot fully destroy every last FeLV virus but it can keep the number of virus low so that no illness results (regressive infections). Finally, there are those cats who remain continuously infected and unable to develop an adequate immune response. Those cats are likely to develop associated diseases within a few years. Sadly most of the cats that become permanently infected with this progressive form of feline leukemia will die within 3-4 years of their diagnosis. Younger cats are particularly vulnerable. I will tell you about these various forms of feline leukemia later.
The destiny of FeLV carrier cats that show no disease (regressive infections) is not preordained. For instance, certain medications such as corticosteroids that suppress natural immunity have been blamed for reactivation of their disease. Environmental stress-related reactivation of the virus has also been proposed. ( read abstracts here & here or ask me for Westman2019 & Hartmann2020 )
Is There More Than One Type Of Feline Leukemia Virus?
Exogenous feline leukemia virus = FeLV
As far as the feline leukemia virus your cat might be exposed to, veterinarians believe that they are all quite similar throughout the world. None of the strains of this virus have been reported as being resistant to the vaccines veterinarians give to your cat to protect it. However, like all virus, there are probably strains or subtypes of the virus that are more pathogenic than others. Veterinarians really do not know. We call all of these “exogenous” feline leukemia virus or FeLV. The most common subtype is FeLV-A. FeLV-A is the variant in cats most often associated with immune system suppression that results in increased susceptibility to secondary infections of all types. Some suggest that Subtype B is the one most associated with tumor formation.
Endogenous feline leukemia virus = enFeLV
Sometime in the ancient past, long before cats were domesticated, wild cats were exposed to the feline leukemia virus. In those that recovered, portions of the feline leukemia’s genetic material (RNA) found their way into the cat’s own DNA instructions that passed down through the generations to the house cats of today. These inherited footprints of past virus exposures are present in all of us. ( read here) Although these fragments of virus code can confuse veterinary PCR test results, these endogenous or provirus are thought to be incapable of becoming infectious or causing disease in your cat. (read here)
FeLV/enFeLV recombinants = FeLV-B
Unfortunately it appears that the common exogenous feline leukemia virus (FeLV) that passes from cat to cat can combine with the endogenous feline leukemia virus enFeLV to form a third type of virus in your cat’s body. Exactly what the presence of this form of the feline leukemia virus means to your cat’s future health is uncertain. Some believe that the presence of FeLV-B makes the later development of lymphoma cancer more likely. (read here) That same article emphasized that the presence of other common “sleeping” (=inactive) virus in your cat (feline foamy virus , feline herpes virus , and feline coronavirus ) might influence how your cat reacts to a feline leukemia virus exposure.
FeLV/subgroup C = FeLV-C
This particular feline leukemia variant is thought to be the one most likely to produce aplastic anemia in your cat. (read here)
Where Did My Cat Catch Feline Leukemia?
If the virus did not pass from mother to offspring, your cat contracted the virus from close contact to another infected cat. That generally requires mouth contact with the oral secretions (saliva) of the infected cat. The longer the two cats were together, the more likely that is to occur. Cats in well adjusted groups often groom each other. Veterinarians theorize that that allogrooming greatly assists the leukemia virus in transferring from cat to cat. Cat fights and bite wounds are theorized to be another, but less common, mode of virus transfer. A third confirmed virus transfer method that I already mentioned is from a mother cat to her kittens. More of those transfers are thought to be after the kittens are born than while they are still in her womb. As cats age they tend to acquire a natural resistance to the feline leukemia virus – or at least to the diseases sometimes associated with it. However that resistance is never absolute.
Could My Cat Have Caught The Leukemia Virus From A Virus-contaminated Environment Such As An Animal Shelter?
That is very unlikely. The feline leukemia virus only survives a few hours outside of a cat’s body at room temperature. (read here) Ordinary household detergents including bleach successfully kill the feline leukemia virus on household surfaces.
If My Cat Is Still Test-Negative For Feline Leukemia What Should I Do To Protect It?
Nothing is as important as keeping your cat indoors and only allowing it outdoors under your close supervision – preferably on a leash.
I believe that the next most important thing you can do is to have your cat vaccinated with a feline leukemia vaccine. I do not know of any studies that confirm the effectiveness of these vaccines in real life situations, but they do meet the precepts (qualifications) of immunology. Your veterinarian may have other thought on that. I personally prefer Boehringer Ingelheim/Merial’s PUREVAX® Recombinant canarypox-vectored FeLV vaccine because it contains no adjuvants and only the portions of the feline leukemia virus thought to be necessary for immunity. (read here)
Before any cat receives this or another brand of FeLV vaccine, I suggest that it be tested to be sure it does not already harbor the active FeLV virus. Although it should not hurt your cat, giving these vaccines will not help cats that are already positive for the leukemia virus. But it will give you a false sense of security that your cat is protected.
You might think that your FeLV- negative cat will never go outside and because of that the vaccine is unnecessary. But life and the future are unpredictable for all of us. When possible, I administer the FeLV vaccine at 12 weeks of age and a second shot 3-4 weeks later. For young cats, I suggest a third shot a year later and never again. In mature FeLV-negative cats with an unknown vaccination history, I believe that a single FeLV vaccination should be sufficient. Some might say that even that is unnecessary because resistance to FeLV-related health issues increases with age.
These vaccines are not foolproof. So if your cat leads a high-risk lifestyle or goes missing, a point-of-care feline leukemia test would be prudent a month after the incident occurred. Co-habitation with other FeLV- cats during that 30 days can present a problem, as can the fact that some cats take much longer than 30 days to become test-positive. Some believe that these vaccines do not prevent infection; that they simply prevent the development of FeLV-related disease. All vaccines given to your cat should be administered low on a rear leg or in the tail to minimize the dangers of inoperable fibrosarcoma formation. ( read here)
What Are The Signs Of Feline Leukemia That I Might See In My Cat?
Because the effects of the feline leukemia virus are so unpredictable and so pervasive, feline leukemia infection is on your veterinarian’s diagnostic possibilities list for a large percentage of cats that arrive at veterinary hospitals in chronic but nebulous (uncertain of cause) health decline. Almost any organ or organs in you cat can be affected – its blood, its skin, its digestive tract, its eyes, its mouth. When those cats arrive, an in-hospital (“point of care”) FeLV/FIV test is usually in order. That is particularly true when your cat did not respond as expected to prior medications that were dispensed or when it relapsed.
Abortive FeLV Infections
The immune systems of a few cats that are exposed to the FeLV virus appear to recognize the virus as a threat and completely eliminate it from their bodies. We do not know if that is due to genetic characteristics of the particular virus that your cat met, the genetic characteristics of your particular cat, both, or due to some other factor(s) still unknown. When tests are at first positive for FeLV and later negative, we call those cases abortive FeLV infections.
Regressive FeLV Infections
In some cats, the exposure to FeLV virus causes the cat’s immune system to produce antibodies and/or other factors that eliminate the virus from its bloodstream but allow the virus to persist in the cat’s body hidden in an inactive form . These are called regressive FeLV infections. Some estimate that approximately 10% of FeLV cases follow this rout. I believe that considerably more than 10% do because the vast majority of regressive cases will never visit a veterinarian to be tested at the intervals required to identify them. That is because those cats look and feel fine. Regressively infected cats are not thought to be able to transmit FeLV to other cats. However some believe that regression is not absolute. That is, there is always a possibility that unknown factors might reactivate the virus at some later date. Veterinarians really do not know.
Progressive FeLV Infections
These are the classical cases that all cat owners and veterinarians dread. Cats with progressive FeLV infections persistently have high levels of FeLV virus in their blood stream and saliva. These are the cats whose health eventually begins to decline. They are also the cats most likely to spread the virus to other cats.
Because this is a progressive disease, symptoms tend to come on gradually. Weight loss is a common first symptom. That might be accompanied or followed by a slight fever. Cats normally run a bit hotter at their veterinarian’s office. So a rectal temperature a bit over 101.5-102.5 F / 38.6-39 C might just be attributable to anxiety. Check your cat’s rectal temperature at home to verify a true fever – if your cat will not be too upset about that. Cats that are feeling under the weather from a variety of health issues often have their third eyelids extended farther over their eyes than normal. But even simple dehydration can produce that. Lethargy and apathy are another common early symptom. Of course just about any health issue could be responsible for that. It is common for these cats to assume an unkempt appearance due to their lack of interest in grooming.
Because the FeLV virus has an affinity for your cat’s bone marrow where its white blood cells and red blood cells are produced, it is common for these cats to return (report) abnormal bloodwork results. When specific WBC numbers are low (particularly the neutrophils ) your cat is likely to loose some of its ability to fight infections. Those could include skin infections, ear infections, sinus infection and mouth infections (gingivitis, stomatitis, etc.). Reactivation of quiescent (dormant) cat health issues such as toxoplasmosis is also possible. ( read here) The lab work reports of FeLV+ cats can also mimic the effects of another virus disease of cats which is now rare in the prosperous nations of the world, panleukopenia. Widespread vaccination of kittens here has made panleukopenia quite rare.
Persistent diarrhea and loss of litter box training occasionally occurs in FeLV+ cats. That is because your cat’s white blood cells and a healthy immune system are required to confine unwanted bacteria of all sorts to the interior of your cat’s intestines and not allow them access to the deeper layers of the intestinal wall or the body interior. ( read here) But more commonly, those cases turn out to be aspects of inflammatory bowel disease or low-grade intestinal lymphoma not attributable to (not caused by) the FeLV virus.
Persistent anemia is also common in progressive FeLV infections. Anemia can be the underlying cause of lethargy, weakness and an unstable gait. When your cat is seriously anemic, its respiration and heart rate is usually elevated. Anemia is also apparent in the paler color of its gums. Your vet can confirm anemia through the findings of a low PVC , Hct , or in some cases low hemoglobin . Most of these FeLV anemias are of the non-regenerative type where your cat’s bone marrow has lost its power to produce new red blood cells. After release into your cat’s blood stream, normal red blood cells only have a lifespan of about 70 to 80 days. Your veterinarian can confirm a non-regenerative anemia by discovering a lack of reticulocytes in your anemic cat’s blood results panel.
When the FeLV virus disables your cat’s immune system, your cat becomes more susceptible to tumors. For reasons unknown, it is your cat’s lymphocytes that are the most susceptible lymphoma (lymphosarcoma) cancer induced by FeLV. (read here) There was a time when veterinarians believed that the FeLV virus was responsible for most cases of lymphoma in cats. Probably because of the widespread use of feline leukemia vaccines, that is no longer the case. ( read here ) Some of these cats have enlarged superficial lymph nodes that can be felt under their skin, some do not.
In female FeLV+ cats, miscarriages and the birth of “fading” kittens is another common event.
On rare occasion, cats that are FeLV+ develop neurological problems that include personality changes, seizures and paralysis. We really do not know if that is a direct result of the FeLV virus or if the presence of the FeLV virus allows other “sleeping” (inactive) virus already present in your cat such as feline herpes-1 (cat flu) to reactivate. (read here)
Despite all that I have written so far, some progressively infected cats will remain healthy for many years before FeLV-related disease eventually develops. We do not know why. Perhaps it is the age at which your cat was first exposed to the virus, perhaps your cat’s unique genetics comes into play, and perhaps it is the characteristics of the particular strain of FeLV in its system. Miraculously, a few FeLV+ cats never develop illness. Recent studies associate that with the level of p27 antigen in their blood. ( read here )
Lymphoma is a cancer of your cat’s lymphocytes . When cancerous lymphocytes form in aggregates as a solid mass, it becomes a lymphoma. When the individual cancerous lymphocytes float free in the blood, it is a leukemia. Depending on where lymphomas form, the symptoms they produce are quite different. Lymphomas in cats are not only associated with the feline leukemia virus, they form spontaneously as the most frequent form of cancer in cats. The most common location for lymphoma tumors to form in FeLV+ or FIV+ cats is in the pet’s chest (a mediastinal lymphoma) where they obstruct breathing and circulation. But lymphomas have the ability to form anywhere that lymph nodes or lymphoid clusters are naturally present. So the signs and symptoms of lymphoma are not specific. They tend to be signs associated with the tumorous cells crowding out adjacent tissues as the mass enlarges.
How Will My Veterinarian Decide If My Cat Has Feline Leukemia?
It will be done through blood tests looking for a specific FeLV antigen core protein called FeLV-p27. The in-office tests that your veterinarian uses are handy variations of the in-laboratory ELISA test. Most of these in-office tests also screen for the presence of the cat immunodeficiency virus. You need to be aware that this point-of-care test is only regarded as an initial screening test. False positives do occur. So a positive FeLV test needs to be followed up by an IFA or PCR test performed at a veterinary diagnostic laboratory to confirm the initial in-office results. Unlike the situation with prior FIV vaccinations, prior feline leukemia vaccinations are not thought to result in false positives. IFA test can yield false negatives in FeLV+ cats early in the disease when the virus has not yet established itself in the cat’s bone marrow. ( ask me for Westman2019.pdf)
I Have A Lot Of Cats, What Should I Do Now That I Know That One Of Them Is FeLV Positive?
All your cats need to be tested. Once you know the FeLV status of every cat you are faced with several choices. You can re-home the positive cats or you can re-home the negative cats. I mentioned that the FeLV virus does not persist long in your home or cattery. So perhaps your house can be divided into two areas – one for each group. You can also attempt to vaccinate the negative cats against feline leukemia, although the amount of protection that might provide will remain unknown. Periodic testing of the negative group still needs to be performed.
What About Testing My New Kitten For Feline Leukemia?
The Idexx SNAP and Zoetis Witness FeLV blood tests can be performed on cats of any age. Unlike blood tests for FIV (which some of these test platforms combine) that look for antibodies cats produce against that virus, these two test brands look for the presence of the FeLV virus itself. However newborn kitten that are actually FeLV+ can still test negative for several weeks to several months after birth. That is because the number of leukemia virus in their blood must reach substantial levels to trigger the positive colorimetric reaction that these tests depend upon. So some veterinarians suggest testing the kitten’s mother instead (if she is available) and delaying testing of the offspring unless the mother turns out to be FeLV+. If one kitten from a litter tests positive, in all probability the entire litter will as well. Another option used in shelters to conserve scant resources is to test a pooled blood sample from the litter. That is an “iffy” (much less desirable) option. A second test of kittens at 4 month of age usually picks up (identifies) FeLV+ kittens that falsely tested negative earlier. Giving those suspect kittens their vaccination at normal ages and intervals is not known to influence the progress of feline leukemia. Some kittens have been known to revert to negative test results with time ( revert to regressive status). When doubt persists, immunofluorescent antibody (IFA) and PCR tests are the most accurate in determining your kitten or cat’s true FeLV status. At some point the ELISA, IFA and/or PCR tests should all agree.
What Treatment Can My Veterinarian Offer My FeLV+ Cat?
The treatments veterinarians can offer your cat are symptomatic (palliative). That is they attempt to deal with the effects of the leukemia virus, not to destroy the virus itself. I mentioned that FeLV+ cats are more susceptible to bacterial infections of all kind. So antibiotics are high on the list of medications dispensed. When it is a FeLV-induced mycoplasma relapse anemia that is being treated, doxycycline is the antibiotic of choice for your cat. In other situations, alternating antibiotics or pulsing them can be helpful. However with time, all bacteria tend to become resistant to antibiotics and creating antibiotic-resistant bacteria in your household is never a good idea.
A more tempting diet prepared at home for your cat can be very helpful in combating the poor appetite and weight loss of feline leukemia. It will also give your cat considerably more pleasure than the industrial stuff sold in cans and bags. Feeding raw meat ingredients are never a good idea when dealing with cats with a depressed immune system. When that is not sufficient, appetite stimulants such as mirtazapine , Entyce/Elura® or cyproheptadine might be helpful.
Medications To Decrease The Likelihood Of Vomiting Or Diarrhea.
Medications such as injectable maropitant (Cerenia®) have been used to control vomiting in cats. Some have used the tablet form “off label” in cats as well. Although maropitant work best when given to treat short term health issues, it has been given for more extended periods. (read here & here ) But when your cat is so ill with FeLV that it cannot hold its food down consistently, I would consider the kindest thing you could do for your friend would be to have it euthanized.
Metronidazole (Flagyl®), tylosin (Tylan®) and diet changes are also sometimes effective in lessening diarrhea. Give probiotics a try as well. Cats do not tolerate oral over-the-counter human anti-diarrheal products well.
I mentioned that anemia due to bone marrow suppression is one of the common effect of the FeLV virus. Since the majority of those cats have lost their ability to produce red blood cells, medications such as darbepoetin to stimulate red blood cell formation (hematopoesis) are rarely effective. Some suggest blood transfusions. But by the time transfusion is required I also believe the much kinder thing to do is to send your cat on to Heaven.
At one time it was hoped that one or more of the antiviral medications discovered to reduce the virus burden in human AIDS patients might help FeLV+ cats. In early trials, all of those medications were found to produce much more serious side effects in cats than they did in humans. The only one that is still occasionally brought up in conversation is raltegravir . In one laboratory tissue culture experiment it appeared to prevent the FeLV virus from multiplying. (read here) In a second experiment, the drug was given to seven FeLV+ cats for 9 weeks. Although the cats’ FeLV virus load decreased during the treatment time, the number of virus in the cats’ blood stream rebounded as soon as the drug was discontinued in all but one of the seven cats. (read here)
There are folks that believe that one can simply “jolt” a failing immune system back into its functional state – like shaking awake up a sleeping person. As tempting as that might sound, I am not one of the people who believes that that is possible.
Polyprenyl Immunostimulant is one of those products. Another is staphylococcus protein-A. A third is interferon Omega (IFN-ω). Another introduced in 2006 was called Lymphocyte T-Cell Immunomodulator (LTCI). Yet another, Virbagen Omega® , a Virbac product marketed in the UK and EU but not as of this writing, in North America. Several of my clients however did successfully obtain Virbagen Omega® here in the USA through a trans-shipper of veterinary pharmaceuticals based in the UK. It never cured a cat. If the cats lives were lengthened or shortened through taking it is something we will never know.
What Treatments Are Possible For Lymphoma?
Lymphomas are composed of cancerous lymphocytes. Corticosteroids temporarily reduce lymphocyte numbers. (read here ) A few cases of FeLV-induced lymphoma appear to temporarily respond positively to corticosteroid medications. But corticosteroid medications such as prednisolone are unlikely to prolong your cat’s life when it faces this cancer. In one study, the median remission and survival times for two FeLV antigen-positive cats were 27 and 37 days. (read here ) Chemotherapy is also possible. But chemotherapeutic drugs often aggravate FeLV bone marrow immunosupression (=less red and/or white blood cells produced in the cat’s bone marrow). A second negative is that cats have a reputation for not tolerating “chemo” drugs as well as dogs or humans do. Major side effects are common. When your cat reaches the point where chemo is under discussion, I believe that euthanasia is the much kinder choice for your feline friend.
When My Cat Is Feline Leukemia Positive What Lifestyle Suits It Best?
As I mention many times on my website, cats that are confined to the indoors live considerably longer than cats that are allowed to roam. Keeping your FeLV+ cat indoors also prevents spread of the virus to other cats in your neighborhood. Since progressive-class FeLV+ cats have lost much of their natural resistance to infectious disease, disease agents found out-of-doors such as those responsible for toxoplasmosis , bartonellosis , leptospirosis and, cryptococcosis might gain the upper hand. FeLV+ cats are probably less likely to survive encounters with those agents, and all of those organisms have the potential to spread from your cat to you. FeLV+ cats are not good candidates for stays at boarding kennels, travel, veterinary hospital inpatient care or group homes either. All of these situations are likely to increase their stress levels.The most important thing you can do for a FLV-positive cat is to minimize the stress in its life and provide it with a peaceful home.
If you are the keeper of many cats, search for a FeLV+ angel who might be willing to give this cat an individual home. People with a heart so expansive are rare – but they do exist. Placing positive cats in herds does not benefit them. If anything, the stress of group living is likely to reactivate regressively-infected FeLV cats and speed the demise of the others.
Some folks believe that cats should eat diets that contain raw meat. ( read here) I discouraged that earlier – particularly when your cat is a FeLV carrier. Raw meat (particularly ground meat and poultry products) are frequently contaminated with Salmonella. The majority of times that cats and dogs are exposed to salmonella they show no symptoms at all or, at the most, a short period of diarrhea. After that, they clear their bodies of the bacteria or remain silent carriers. (read here & here ) However, your FeLV+ cat is unlikely to have the robust immune system necessary to defend itself from salmonella and other pathogens such as listeria that can be present in uncooked diets. (read here & here ) Raw diets are a potential threat to FeLV+ cats and through them, to you.
FeLV+ cats might benefit from a visit to their veterinarian for a checkup every six month or the visit of a house call vet. Politely avoid sales pitches for unnecessary add on products – they are a sign of the times. What you are there for is a weigh in, your veterinarian’s physical exam and observations and based on that, the possibility of the need for blood and urine analysis.
Just as importantly, purchase an accurate scale and keep a weekly log of your cat’s weight yourself. Human AIDS is also a retrovirus. In people, weight loss is one of the best indicators of AIDS-related decline. (read here) At the first signs of a downward trend, see if diet changes or the appetite enhancers I mentioned earlier might reverse it. A home cooked diet is often the best answer to stretching your cat’s remaining time. (read here)
I would forgo future vaccination boosters for FeLV+ cats. That is particularly important when it comes to vaccines that contain any living agents. Rabies vaccines marketed in the United States are all killed virus products. So they should pose no threat of causing rabies. But it is a false assumption to think that a rabies vaccination will produce an effective protective antibody titer in an immunosuppressed cat. Government regulators prefer to ignore that. (read here) Regarding government-mandated rabies vaccinations, I am not encouraging you to violate the laws where you reside. Future vaccinations of FeLV+ cats against FeLV provide no benefits either. (read here)
My Last Cat Died From Feline Leukemia. When Will It Be Safe To Get Another Cat Or Kitten?
Because the leukemia virus does not survive long in the environment; and provided you have no other untested cats, you can accept a new cat or kitten at any time. Before you do, that cat or kitten (and preferably its mother) needs to be tested for FeLV. Don’t rush or get talked into doing so too soon. There will always be people rushing you to do so because there is always an oversupply of homeless cats. But people need time to adjust and accept the loss of loved ones. You need that time. By all means make a donation in your cat’s memory to a fund that places homeless cats, but wait until the time is right for you to accept another cat.
Can The Feline Leukemia Virus Infect Me?
Feline leukemia does not affect humans and it is not related to the leukemias that affect mankind. The FeLV virus does not infect dogs either, but it has been reported in lions, tigers and other non-domestic cats.