What is Feline Leukemia?
Feline Leukemia (FeLV) is caused by a contagious retrovirus. Retrovirus means it can be incorporated into a cat’s genome and may not be cleared over time. Eventually, FeLV has the potential to impact a cat's immunity and cause various diseases, including cancerous tumors. FeLV is the most common cause of cancer in cats. FeLV is not transmissible to humans or other animals.
However, a persistently infected cat sheds the virus via saliva, feces, urine, and milk. Transmission can take place from an infected mother to her kittens before they are born or through her milk. Other ways the FeLV virus passes from cat to cat are prolonged close contact (co-grooming, sharing food bowls, sharing litter boxes) or bite wounds. Though any cat exposed to the virus can develop an FeLV infection, kittens are at a greater risk than adult cats due to their immature immune system.
There is some good news. FeLV does not survive long outside a cat's body – probably less than a few hours under normal household conditions - so it is unlikely for a cat to be infected from the environment without prolonged close contact with an infected cat. Also, not every cat infected will develop full-blown Feline Leukemia.
Symptoms:
Upon exposure, a cat’s body can react to the FeLV in different ways, leading to abortive, regressive, or progressive infections.
Abortive
In the best-case scenario, the exposed cat will mount an effective immune response against the virus and eliminate it before the virus becomes incorporated into the cat’s genome. This is an abortive infection, and testing for the virus will be negative. These cats will have antibodies against FeLV and are considered immune to the disease. Abortive FeLV cats will test negative for the virus and will have no signs of the disease, so owners and veterinarians will likely be unaware that they were infected. Abortive FeLV cats cannot pass the virus on to other cats and kittens.
Regressive
30-40% of exposed cats will have a semi-effective immune response to FeLV and will develop a regressive infection. In these instances, the virus is incorporated into the cat’s genome, but the immune system prevents continued viral replication, so there are no viral particles present in the cat’s blood after the initial infection. A cat with a regressive infection cannot infect other cats with the virus, and is not likely to have symptoms from FeLV. However, in regressive cases, the virus can reactivate and resume replicating if the cat's immunity is negatively impacted by illness or medications. When this happens, the cat becomes progressively infected, is infectious to other cats, and is at risk of developing related illnesses.
Progressive
The worst-case scenario is a progressive FeLV infection. Cats with progressive FeLV are at high risk of developing potentially fatal diseases. With a progressive infection, a cat’s bone marrow becomes infected with the virus and allows continual viral replication. Cats with progressive FeLV infection shed viral particles and can infect other cats. Studies suggest that 30-40% of cats exposed to FeLV develop a progressive infection, with kittens at a higher risk due to their immature immune systems.
Clinical Signs:
During the early stages of infection, cats may not exhibit any signs. Over weeks, months, or even years a FeLV-infected cat's health can progressively deteriorate or they may have cycling illnesses. Symptoms can include:
- Loss of appetite
- Weight loss
- Poor coat condition
- Enlarged lymph nodes
- Fever
- Pale gums or inflammation of the gums
- Skin, urinary bladder, and/or upper respiratory tract infection
- Chronic diarrhea
- Seizures, behavior changes, and other neurological disorders
- Eye conditions
- Reproductive failure
The symptoms above can be caused by other health issues, as well. If your cat or kitten displays one of more of them, make an appointment to have them checked as soon as possible.
Testing:
Testing for Feline Leukemia is recommended in several scenarios. Testing a new cat prior to its adoption into a household with other cats is highly important. Testing is also recommended for any cat that has been exposed to another cat of unknown FeLV status. Routine testing on an annual basis is recommended for all cats, but is particularly important for outdoor cats. Keep in mind, FeLV tests are not 100% accurate. They can produce false negatives and false positives for a variety of reasons.
False negatives can result from:
- A low sensitivity test.
- An early infection where the virus hasn't replicated enough to be detected.
- A regressive infection that was once positive but is now in remission.
- A test that is run too early in a kitten that hasn't developed enough antibodies for the test to detect. Testing in kittens is recommended after six months of age.
False positives can result from:
- A low specificity test.
- A kitten that is still showing maternal antibodies. Testing in kittens is recommended after six months of age.
Note: FeLV vaccines will not cause false-positive test results. In the case of a positive test, further or repeat testing should be conducted to confirm. This will prevent unnecessary worry, treatments, and potential euthanasia of healthy cats in a shelter environment.
Prevention:
Vaccination for FeLV is available, but it doesn't provide 100% protection. It is a core vaccine for all kittens, due to their higher risk of infection. The vaccine is also recommended to reduce the risk of FeLV infection for cats at risk of exposure, such as indoor/outdoor cats. Owners contemplating FeLV vaccination for their uninfected cats should consider the cats' risk of exposure to FeLV-infected cats and discuss the advantages and disadvantages of vaccination with a veterinarian.
Since not all vaccinated cats will be protected by the vaccine, preventing exposure remains important for ALL cats. Start by keeping your cat indoors and away from other potentially infected cats. If outdoor access is allowed, make sure your cat is spayed/neutered and provide supervision to prevent fighting, scratching, biting, or mating behaviors, which easily transmit the disease. You may also provide an enclosed outdoor space, or "CAT-io," to prevent wandering and fighting.
If introducing a new cat to a home that already has cats, be sure to test them before bringing them into the environment. Ideally, infection-free cats should be housed separately from FeLV-positive cats with no sharing of food and water bowls or litter boxes between the two. Unfortunately, many FeLV-infected cats are not diagnosed until after they have lived with other cats. In this case, all other cats in the household should be tested for FeLV.
Prognosis:
Getting a diagnosis of Feline Leukemia can be shocking and scary for cat parents. It is important to remember that cats with FeLV can live a normal life for prolonged periods of time. The average survival time following this diagnosis is 2.5 years. However, some cats go on to develop a regressive infection and can live much longer without symptoms or being contagious. If your cat has tested positive and this has been confirmed with further testing, it is important to carefully monitor their health.
FeLV positive or not, if you notice changes in your cat's activities, weight, appetite, bowel or bladder habits, or the appearance of their skin, mouth, or eyes, schedule an appointment to have their health checked.
If you have questions about this article or feel you need a consultation, contact us for an appointment at
336-644-1522