What is Feline Leukemia?
Feline leukemia virus (FeLV) is one of the most common infectious diseases of cats in North America.1 The prevalence of this disease can vary depending on the population in question. In some cats, the disease can worsen over time and be fatal. There is no cure for this disease.
Feline leukemia virus is quite different than what you think of with a human leukemia diagnosis. FeLV only affects cats, it cannot be spread to dogs, humans, or any other species. It is a virus that causes immune suppression, anemia, or other types of cancers, often leading to death within three years of diagnosis. It is important to note that there are different stages of infection, which is why some cats are very ill and others did not show any clinical signs at the time of diagnosis. The stage of infection also greatly affects their prognosis, or how long they can live with the virus.
Abortive Infections
This is the best possible outcome where a cat is infected and tests positive for antibodies against the virus, but is able to overcome infection. Unfortunately, this ideal outcome is the rarest.
Regressive Infections
These cats are initially positive for leukemia but can mount an immune response to clear the infection from the blood. This immune response is not enough to fully eliminate the virus from other parts of the body though, allowing the virus to hibernate. These cats will likely test negative and not be able to infect other cats. However, the virus lingering in the body can become active again in the future causing illness and the cat will again be contagious. This type of response happens in about 10% of infected cats.
Progressive Infections
These cats have active infection with virus in their bloodstream, but inadequate immune response to fight it. They are likely to develop FeLV associated disease.
Cats infected by the virus can develop a variety of secondary disorders, such as:
- Gastrointestinal issues such as diarrhea
- Cancer (especially lymphoma and leukemia)
- Suppression of the immune system (increasing risk of other infections including viruses, bacterial or fungal infections)
- Immune mediated diseases (cat’s immune system attacks its own cells)
- Intestinal inflammation
- Neurological disorders such as blindness
- Stomatitis (severe inflammation of the mouth)
Feline Leukemia is Contagious
Cats that do not clear their infection, or before they clear their infection, are primary sources of infection for other cats. The virus is shed largely in saliva, but can also be in nasal secretions, urine, feces, and even the milk of cats infected with the virus.
Cat-to-cat transmission is common from friendly, intimate, or aggressive behaviors. This may include bite wounds, mutual grooming, sharing bowls, and litter boxes. It can also be transmitted from a mother cat to her kittens either in utero or while nursing. FeLV does not live long outside of a cat’s body, so it is most likely transmitted when cats have direct contact with one another.
Your Cat’s Risk of Infection
Exposure to infected cats dramatically increases your cat’s chances of contracting FeLV, especially for kittens and young adult cats. Older cats are less likely to contract the infection because resistance to infection seems to increase with age.
For indoor-only cats, the risk of contracting FeLV is low due to the decreased chance of encountering already infected felines, especially ones that they may fight. However, cats in multi-cat households are more at risk, especially if they share water and food dishes as well as a litter box.
The prevalence of FeLV has decreased over the last 25 years because of vaccines, testing, and awareness.
FeLV is the leading cause of cancer in cats, can cause blood disorders, and potentially lead to immune deficiencies that decrease a cat’s ability to protect itself from other infections. This allows bacteria, viruses, and other infections that wouldn’t normally affect a healthy cat to potentially cause severe illness.
During the early stages of infection, a cat may not exhibit any signs of infection at all. In fact, it may take weeks, months, or even years for a cat to begin to display signs of infection due to the different stages of disease as discussed above.
Clinical Signs May Include:
- Loss of appetite
- Progressive weight loss
- Poor coat condition
- Enlarged lymph nodes
- Fever
- Pale gums and other mucus membranes
- Inflammation of the gums and/or mouth
- Infections of the skin, urinary bladder, and/or upper respiratory tract
- Diarrhea
- Seizures, behavior changes, and other neurologic disorders
- Variety of eye conditions
- Reproduction failures
FeLV is diagnosed with a blood test. Your vet may recommend a test when you first adopt your cat, before vaccinating against the virus, after exposure to the virus (such as a cat bite wound), or if the cat is ill.
There are two types of blood tests used to diagnose FeLV which detect a protein in the virus called p27.
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• Enzyme-linked immunosorbent assay (ELISA) detects free FeLV particles that are commonly found in the bloodstream during both early and late stages. This is typically done in the vet’s office as a screening tool.
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• Indirect immunofluorescent antibody assay (IFA) is typically performed after a positive ELISA to confirm the diagnosis. This test detects virus particles within white blood cells, which typically indicates advanced infection. This test is usually sent out to a diagnostic lab.
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• A third test, polymerase chain reaction or PCR, is sometimes used to define the stage of infection and gain more information about the cat’s infection.
Treatment
Unfortunately, there is no cure for FeLV. However, there are some methods to decrease the amount of FeLV in the bloodstream of infected cats. These therapies may have significant side effects. Vets managing FeLV-positive felines usually treat specific problems or secondary disorders rather than the FeLV directly.
Prevention
Preventing exposure to FeLV infected cats is the most effective method help protect your cat from FeLV. Try keeping cats indoors, but if the cat is allowed outside, consider supervising them or keeping them in an enclosure to avoid interaction with other cats.
All cats should be tested for FeLV prior to introducing them into a home with other cats. If any cats are positive for FeLV they should be kept separate with their own litter boxes, food and water bowls. If a cat at home tests positive, be sure to test all other cats.
Effective vaccines are available to help prevent FeLV. The recommendation is for all kittens less than 1 year of age to receive the initial series of the vaccine and then repeat annual vaccination depending on lifestyle. Discuss your cat’s FeLV vaccine schedule with your veterinarian.
Prognosis of Feline Leukemia
A diagnosis of FeLV can be emotional and confusing. Remember that cats with FeLV can live normal lives for extended periods of time. The median survival time is 2.5 years. After FeLV is confirmed, monitor for any abnormalities in your cat and be sure to seek care immediately.
