Last updated: April 27, 2026

Feline Leukemia Virus (FeLV): A Complete Guide for Cat Owners

Feline leukemia virus (FeLV) is one of the most significant infectious diseases in cats worldwide. Once considered an automatic death sentence, a FeLV diagnosis today carries a much more nuanced prognosis. Advances in understanding the virus, improved diagnostic testing, and better supportive care have changed what it means for a cat to be FeLV-positive. Many FeLV-positive cats live comfortable lives for years after diagnosis with attentive care, while others may develop serious complications more quickly. Understanding the virus — how it spreads, what it does in the body, and how to manage it — empowers cat owners to provide the best possible care for affected cats and protect uninfected cats in their household.

FeLV is a retrovirus — the same class of virus as HIV in humans — that integrates its genetic material into the host’s DNA. This integration is what makes FeLV so challenging: once the virus establishes a persistent infection, it cannot be eliminated from the body. The virus primarily attacks the immune system and bone marrow, leading to immunosuppression that makes affected cats vulnerable to secondary infections, anemia, and certain cancers. However, not every cat exposed to FeLV develops a persistent infection — a significant percentage of cats successfully fight off the virus through their immune response.

How FeLV Spreads Between Cats

FeLV is transmitted primarily through prolonged close contact between cats. Understanding the routes of transmission is essential for prevention and for managing multi-cat households.

Saliva. Saliva is the primary vehicle for FeLV transmission and contains the highest concentration of virus. Mutual grooming, sharing food and water bowls, and bite wounds are the most common routes of transmission. Cats that groom each other extensively are at particularly high risk. Casual contact — brief nose-touching or being in the same room — is much less likely to transmit the virus.

Nasal secretions. Nasal discharge from infected cats contains virus and can spread FeLV through close face-to-face contact, sneezing, and shared spaces where secretions accumulate.

Blood. Blood-to-blood contact, primarily through bite wounds during fights, is another significant transmission route. This is particularly relevant for outdoor cats and intact males that are more likely to engage in territorial fights.

Mother to kitten. Infected queens can transmit FeLV to their kittens in utero (across the placenta), during birth, and through nursing (milk contains virus). Kittens infected by their mothers often develop persistent infections because their immature immune systems cannot mount an effective response.

Urine and feces. While FeLV can be present in urine and feces, these are considered minor transmission routes compared to saliva and blood. Shared litter boxes are a theoretical but low-risk transmission route.

FeLV is a fragile virus that does not survive long outside the cat’s body — typically only a few hours in a dry environment. It is easily killed by routine cleaning with soap and water, common disinfectants, and drying. This environmental fragility means that indirect transmission (through contaminated objects or environments) is uncommon, and new cats can safely be introduced to a household after an FeLV-positive cat has been removed, with basic cleaning. If you are bringing a new cat into your home, testing for FeLV before introduction is strongly recommended.

What Happens After FeLV Exposure

Not every cat that encounters FeLV becomes permanently infected. The outcome after exposure depends on the cat’s age, immune status, viral dose, and duration of exposure. There are several possible outcomes.

Abortive infection. Some cats, particularly healthy adults with strong immune systems, mount an effective immune response that eliminates the virus before it establishes systemic infection. These cats may test positive briefly on some tests before reverting to negative. They develop immunity and are resistant to future infection.

Regressive infection. In regressive infection, the cat’s immune system controls viral replication effectively but does not completely eliminate the virus. The viral DNA remains integrated in the cat’s cells, but active virus production is minimal or absent. These cats test negative on standard antigen tests (ELISA/SNAP) but may test positive on PCR testing. Regressively infected cats are generally healthy and are not considered contagious under normal circumstances. However, severe immunosuppression (from illness or medications) can theoretically reactivate the virus.

Progressive infection. In progressive infection, the virus overcomes the immune response, establishes persistent viremia (virus circulating in the blood), and infects the bone marrow. Progressively infected cats test positive on both antigen tests and remain positive. They continuously shed virus and are contagious to other cats. Progressive infection carries the most serious prognosis — these cats are at risk for FeLV-related diseases including immunosuppression, anemia, lymphoma, and other complications.

Age and susceptibility. Kittens are much more susceptible to developing progressive FeLV infection than adult cats. Kittens under four months of age that are exposed to FeLV have a 50 to 80 percent chance of developing persistent infection, while healthy adult cats exposed to FeLV have only a 10 to 30 percent chance. This age-related resistance is due to the maturation of the immune system and highlights the importance of testing and protecting young kittens.

Symptoms of FeLV in Cats

FeLV-positive cats may remain apparently healthy for months to years before developing clinical signs. The virus can affect virtually any organ system, producing a wide range of symptoms depending on what complications develop.

Immune suppression. The most common consequence of FeLV is gradual immune suppression, making affected cats vulnerable to secondary infections that healthy cats would easily fight off. Recurring upper respiratory infections, chronic gingivitis and stomatitis (severe mouth inflammation), persistent skin infections, slow wound healing, chronic diarrhea, and recurring urinary tract infections are all common manifestations. These secondary infections are often the first clinical sign that prompts FeLV testing. The oral inflammation seen in FeLV cats can be similar to feline stomatitis from other causes.

Anemia. FeLV frequently causes anemia — a reduction in red blood cells — through several mechanisms. The virus can directly suppress red blood cell production in the bone marrow, cause immune-mediated destruction of red blood cells, or lead to blood loss through secondary infections. Signs of anemia include pale gums, weakness, lethargy, rapid breathing, decreased appetite, and weight loss. Anemia is one of the most common and serious complications of FeLV.

Lymphoma and other cancers. FeLV is the most common cause of cancer in cats. The virus can trigger the development of lymphoma (cancer of lymphocytes) in various locations including the chest (mediastinal lymphoma), abdomen, kidneys, spinal cord, and nasal passages. Lymphoma signs depend on the location but may include difficulty breathing, abdominal swelling, weight loss, loss of appetite, vomiting, diarrhea, or neurological signs. Leukemia — cancer of the white blood cells — can also develop.

Other complications. FeLV can cause a variety of additional problems including reproductive failure (infertility, fetal resorption, stillbirth), neurological disease (hind limb weakness, urinary incontinence, behavior changes), and kidney disease. Some cats develop an FeLV-associated enteritis that causes chronic weight loss and diarrhea despite adequate nutrition.

Testing and Diagnosis

FeLV testing is straightforward, widely available, and should be performed routinely in several situations: when adopting any new cat regardless of age, when a cat has been exposed to a known FeLV-positive cat, when a cat is ill (especially with recurrent infections), before initial FeLV vaccination, and periodically for cats with ongoing outdoor access or potential exposure.

ELISA/SNAP test. The most commonly used screening test is the ELISA (enzyme-linked immunosorbent assay), available as a point-of-care SNAP test that provides results in approximately 10 minutes using a small blood sample. This test detects FeLV p27 antigen in the blood, indicating active viral replication. A positive SNAP test indicates current viremia but does not differentiate between transient and persistent infection. Because false positives can occur, any positive screening test should be confirmed.

IFA (immunofluorescent antibody) test. The IFA test detects FeLV antigen within white blood cells and platelets in a blood smear. A positive IFA test indicates that the virus has infected the bone marrow and the infection is almost certainly persistent (progressive). IFA testing is often used to confirm a positive ELISA result. A cat that is ELISA-positive but IFA-negative may have an early or regressive infection and should be retested in 30 to 60 days.

PCR testing. Polymerase chain reaction (PCR) testing detects FeLV DNA or RNA and is the most sensitive test available. PCR can identify regressively infected cats that test negative on antigen tests. It is most useful for confirming discordant results, testing cats with suspected regressive infections, and epidemiological studies.

Retesting protocol. Because the outcome of FeLV exposure takes time to determine, retesting is important. A cat that tests positive should be retested in 30 days to differentiate transient from persistent infection. A cat that tests positive on both the initial test and the 30-day retest is very likely to have a persistent, progressive infection. Cats that revert to negative on retesting likely had a transient or regressive infection and have a much better long-term prognosis.

Caring for an FeLV-Positive Cat

A diagnosis of FeLV does not mean immediate decline or death. Many FeLV-positive cats live comfortably for years with appropriate care and management. The key pillars of care include preventing secondary infections, monitoring health closely, and maintaining quality of life.

Indoor-only lifestyle. FeLV-positive cats should be kept strictly indoors for two reasons: to prevent spreading the virus to other cats and to reduce their exposure to pathogens in the outdoor environment that their compromised immune system may struggle to fight.

Separation from FeLV-negative cats. Ideally, FeLV-positive cats should be housed separately from FeLV-negative cats to prevent transmission. If separation is not possible, the risk of transmission between adult cats in casual contact (without mutual grooming or shared food bowls) is relatively low, but it is not zero. All FeLV-negative cats in the household should be vaccinated against FeLV. The decision to house FeLV-positive and negative cats together should be made in consultation with your veterinarian.

Nutrition. A high-quality, balanced commercial diet supports immune function and overall health. Avoid raw meat or unpasteurized dairy products, as the immunocompromised cat may be more susceptible to foodborne pathogens. Maintain a healthy body weight — both obesity and underweight can compromise health.

Veterinary monitoring. FeLV-positive cats should see the veterinarian at least twice yearly — more frequently than the annual visits recommended for healthy cats. These visits should include a thorough physical examination, complete blood count (to monitor for anemia and white blood cell changes), blood chemistry panel, and urinalysis. Prompt attention to any illness — even seemingly minor ones — is important because the immunocompromised cat’s ability to fight infection on its own may be limited. Regular dental care is especially important since oral disease is common in FeLV-positive cats.

Parasite prevention. Keeping FeLV-positive cats current on parasite prevention (fleas, ticks, intestinal worms, heartworm) is important to reduce the disease burden on an already compromised immune system.

Stress reduction. Minimizing stress supports immune function. Provide a stable, enriched environment with consistent routines, adequate resources (food, water, litter, resting spots), and opportunities for play and mental stimulation. Avoid unnecessary changes and ensure the cat feels safe in its environment.

Vaccination considerations. FeLV-positive cats should receive core vaccinations (rabies and FVRCP) to protect against other diseases, though the immune response to vaccines may be reduced. Modified live vaccines should generally be avoided in immunocompromised cats — killed or recombinant vaccines are preferred. Discuss the vaccination protocol with your veterinarian.

Frequently Asked Questions

How long can a cat live with FeLV?

The prognosis for FeLV-positive cats varies widely. Studies suggest that approximately 50 percent of cats with progressive FeLV infection succumb to FeLV-related disease within two to three years of diagnosis, and approximately 80 percent within four to five years. However, some FeLV-positive cats live much longer — five, eight, or even ten years — particularly if they remain in the latent or early stages of disease. Cats with regressive infections (those that test negative on antigen tests after initial positive results) have a much better prognosis and may live normal lifespans. Individual variation is significant, and no prediction can be made with certainty for any individual cat. Providing excellent nutrition, regular veterinary care, and a stress-free environment gives FeLV-positive cats the best chance at a longer, healthier life.

Can FeLV be transmitted to humans or dogs?

No. Feline leukemia virus is species-specific and cannot infect humans, dogs, or other non-feline species. Despite being a retrovirus (the same class of virus as HIV), FeLV poses no risk to human health. You can safely handle, pet, and care for an FeLV-positive cat without any risk of infection. Similarly, dogs in the household are not at risk. The only animals that can be infected by FeLV are domestic cats and some closely related wild feline species.

Should I adopt an FeLV-positive cat?

FeLV-positive cats make wonderful companions and are among the most difficult shelter animals to place. If you have no other cats, or if all cats in your household are FeLV-positive or vaccinated against FeLV and you accept a degree of transmission risk, adopting an FeLV-positive cat can be deeply rewarding. These cats deserve loving homes just as much as any other cat. Be prepared for the possibility of more frequent veterinary visits and potential medical costs, and understand that the cat’s lifespan may be shortened. Many rescue organizations and shelters have FeLV-positive cats available for adoption and can provide guidance on their care.

Is the FeLV vaccine effective?

The FeLV vaccine is considered effective at reducing the risk of persistent infection, though no vaccine provides 100 percent protection. Studies show the vaccine reduces the risk of persistent FeLV infection by approximately 70 to 80 percent. The FeLV vaccine is classified as a non-core vaccine — recommended based on risk assessment rather than for all cats universally. It is recommended for kittens (all kittens should receive the initial FeLV vaccination series), outdoor cats, cats in multi-cat environments with unknown FeLV status, and cats that may have contact with FeLV-positive cats. The initial series consists of two doses given three to four weeks apart, with boosters every one to two years depending on ongoing risk. Importantly, the vaccine is only effective in cats that are FeLV-negative at the time of vaccination — it has no therapeutic benefit for cats already infected.

Can an FeLV-positive cat live with FeLV-negative cats?

This is one of the most commonly asked questions and one of the most debated topics in feline medicine. The ideal recommendation is to house FeLV-positive cats separately from FeLV-negative cats to eliminate transmission risk. However, real life often presents situations where complete separation is not feasible. If FeLV-positive and negative cats must share a household, the following measures reduce (but do not eliminate) transmission risk: vaccinate all FeLV-negative cats against FeLV, provide separate food and water bowls, provide separate litter boxes, prevent mutual grooming (which is difficult to control), and monitor all cats regularly with FeLV testing. The risk of transmission between adult cats in casual contact (without grooming, fighting, or sharing bowls) is relatively low. Discuss the specific situation with your veterinarian to make an informed decision.