FeLV (Feline Leukemia Virus)
Written by Small Door's medical experts
Feline Leukemia Virus (FeLV) is one of the more common infectious diseases diagnosed in cats. Most people associate the word leukemia with cancer, because in humans it refers to a cancer of the blood and bone marrow. In felines, however, leukemia is a virus that can cause cancer. Since its discovery over 50 years ago, widespread testing and vaccination efforts have helped reduce its frequency.
In This Article
Repeated studies have shown that the prevalence of FeLV infection in the general cat population is about 2–3%. Young kittens are at the highest risk for contracting the virus; however, cats can become infected at any age. Outdoor cats, unneutered males, and those with other diseases also have a higher risk of infection.
FeLV is the second leading cause of death of cats in the United States; 85% of persistently infected cats (i.e., cats that are unable to eliminate the infection) die within 3 to 5 years of diagnosis. In kittens, the prognosis is even worse, with the infection almost always proving fatal before the kitten’s first birthday.
On a more hopeful note, a feline leukemia diagnosis does not always indicate an automatic death sentence: 70% of cats seem capable of resisting or eliminating the virus on their own. In these cases, the cat can go on to live a normal life. Otherwise healthy cats who become infected with FeLV and remain positive can still live several years longer, assuming there are no additional complications or secondary infections. (For these cats especially, proper veterinary care is vital.)
Feline leukemia can affect any organ in the body, so the symptoms can vary. Because additional conditions can develop as a result, signs may also be indicative of concurrent diseases or secondary infections.
If infected with FeLV, your cat will most likely display one or more of the following:
Weight loss / loss of appetite
Enlarged lymph nodes
Recurring or chronic illness
Bladder, skin, and other respiratory infections
Changes in eye color or appearance
Severe dental or periodontal disease, especially at a young age
Feline leukemia attacks the immune system, which in turn weakens the cat’s ability to fight off other infections and illnesses. Often, the secondary infections are what become harmful to the cat. In the early stages of infection, signs of the disease are often invisible. Health deteriorates over time, taking weeks, months, or even years. The progression can be quick and consistent, or manifest in repeating cycles of illness followed by relative health.
FeLV is a virus that affects the blood and suppresses a cat’s immune system; it can cause various other blood diseases as well. FeLV makes it difficult for the body to protect itself against infection from bacteria and other viruses.
Feline leukemia is transmitted between cats through close contact; it is often referred to as “the social cat’s disease.” The primary mode of transmission is through saliva, although the virus can also be shed through an infected cat’s urine, nasal secretions, feces, and milk.
Possible methods of transmission include the following:
Sharing water bowls
Using the same litter box
Infected female cats can also pass the virus along to a fetus during pregnancy, and to nursing kittens through milk. This type of “vertical” transmission (from mother cat to kitten) is a very common cause of FeLV infection.
Currently, researchers believe there are four different classes of FeLV infection:
Abortive infections: The exposed cat produces an effective and early immune response. This prevents viral replication and eliminates virus-infected cells. During the abortive stage, the cat seems to clear the infection and is likely no longer contagious. Approximately 70% of all cats infected as adults may fall into this category.
Regressive infections: Viral replication is limited, but a small population of infected cells remain. These cats are antigen-negative, but the virus can be detected in a small percentage of blood tests through a specific type of DNA blood test (polymerase chain reaction, or PCR). It is unclear, however, whether these cats truly eliminate all of the virus from their system, and they may or may not remain contagious.
Latent infections: A moderate amount of infected cells remain. These cats are antigen-negative but PCR-positive. As long as the infection remains latent, the cats are not contagious. However, the virus may become reactivated at any time, resulting in the typical clinical signs of FeLV infection.
Progressive infections: Virus replication is not eliminated; both viral antigens and genetic material can be detected in the blood. The cat is actively shedding the virus and is likely to become ill with FeLV-related diseases.
It’s important to note here that our understanding of FeLV is changing all the time. For example, some scientists doubt whether FeLV can ever truly be “aborted” or eliminated. Conversely, as cats receive increasingly improved medical care and better home care by their owners, some FeLV-positive cats are apparently living longer and healthier lives than would have been previously expected.
In the vast majority of cases, a blood test will detect the virus. Occasionally, however, bone marrow is examined to confirm infection.
Diagnostic testing may include:
Blood chemistry test
Bone marrow aspiration
Specialized antibody tests
The ELISA (enzyme linked immunosorbent assay) is the most commonly used test to detect FeLV infection. A blood sample is required in order to detect the presence of leukemia viral antigen (proteins or cell markers unique to the leukemia virus).
Testing is recommended when cats are first acquired, before vaccinating, if there has been potential exposure, or if they have been bitten by another cat. Annual testing should be done on cats that live in a household with other FeLV-positive cats or if they have outdoor access. For cats going into a new home or known to be at high risk of exposure, testing should be repeated 60 days after the first test, in case a recent infection has not yet presented itself.
There is no medication that can wipe out FeLV, but supportive treatment is available to help with symptoms. Steroids, antiviral drugs, chemotherapy, and blood transfusions may be utilized to manage feline leukemia.
Steroids are used to treat cancerous lymphocytes in the blood, but they can also leave a cat open to developing other diseases, because steroids further weaken the immune system. An antiviral can reduce the amount of virus present in the blood and is easier on the body than chemotherapy. However, antivirals are very expensive, and it is currently unclear how helpful they may be. Antibiotics are given when any bacterial infections arise. Blood transfusions may also be necessary in the case of severe anemia.
Is There a Cure for FeLV?
There is no cure for the virus, and persistent infection is almost always fatal. However, barring any major disease complications and secondary infections, cats infected with FeLV as adults can still have a reasonable quality of life with routine veterinary care, proper feeding, and good at-home care. Average survival time after diagnosis is around 2.4 years, but some cats will appear “healthy” for many years. Sadly, the disease progresses faster in kittens, with fewer than 5-10% of infected kittens surviving to one year of age.
Is FeLV Contagious for Humans and Other Pets?
FeLV is contagious between cats. But at this time, it cannot be transmitted to humans or other animals.
What Is the Cost for Treating FeLV?
First, there is the cost of the diagnostic exam, which will vary by vet. (As always, the cost for medical care is generally higher in larger cities.) The cost of the FeLV ELISA blood test can run between $50–$75, but may be more depending on where you live; additional testing will add to the bill, as will additional vet visits, supportive care, and medications.
Cats diagnosed with FeLV as adults can live relatively normal lives for some time with proper management and care. Keep an eye out for things such as:
Litter box habits
Appearance of the eyes and mouth
Regular vet visits at least every 6 months are important for monitoring the disease and looking out for any secondary infections. Your vet will also make recommendations for appropriate vaccinations to protect against additional feline viruses. The FeLV vaccine does not offer protection once a cat is infected with the virus.
As an owner, there are a number of preventive measures you can take to decrease your cat’s risk of contracting or spreading FeLV:
Adult cats can be tested, then vaccinated if they are negative. If there is a continuing risk of exposure to the virus, booster vaccinations are generally given to adult cats.
Kittens are the most vulnerable to FeLV and should be vaccinated with a recombinant vaccine. Leukemia is almost completely preventable with just two kitten vaccines and a booster a year later.
All cats that test negative by the first ELISA blood screening test but are surrounded by possible exposure should be retested in 60 days. All newly adopted kittens should be tested twice: once right after adoption (unless already tested by the shelter or rescue group), and then again in 60 days.
All infected cats should be neutered after receiving a positive diagnosis to prevent the possibility of passing the virus on to offspring.
Infected cats should be housed indoors and kept away from other cats, both to limit the risk of infecting other cats as well as to avoid contracting other infections.
Is There a Vaccine for FeLV?
There is a vaccine for FeLV. Kittens are usually vaccinated at around 8–12 weeks of age, then given booster vaccinations three or four weeks later. Yearly boosters are given as long as cats are at risk for exposure. These include cats that live with other cats or are allowed to go outdoors. If a cat is considered to be at low risk for FeLV, your vet may recommend not vaccinating. It’s best to talk with your doctor and weigh the options.
Vaccinations and limiting exposure are the best ways to prevent your cat from contracting FeLV. Once infected, cats cannot be cured of FeLV, but with proper management and care they can enjoy a normal life for a few years after the initial diagnosis.