Feline Leukemia Virus (FeLV) in Cats: Symptoms and Treatment

Feline leukemia virus (FeLV) is a virus affecting approximately 2% of the feline population.  

The potential outcomes for this virus vary, with some cats showing no symptoms and some cats developing life-threatening disease.  

FeLV is the most common cause of cancer in cats.  

There are steps you can take to protect your cat from FeLV.  

In this article, you’ll learn what this virus is, symptoms to watch for, how the virus is managed, and preventative strategies to keep your cat healthy. 

What Is Feline Leukemia Virus (FeLV)?

Feline leukemia virus is a common infectious disease that affects about 2% of cats in the United States.  

It’s spread cat-to-cat and leads to the destruction of the cat’s white blood cells and immune system. This leaves them more susceptible to infection, cancer, and death.  

The leukemia virus attacks the cat’s blood cells by invading tissue that makes up the blood cells, including bone marrow and lymph tissue.  

Blood cells (red blood cells, white blood cells, and platelets) play an important role in keeping the body supplied with oxygen and nutrients. These cells help fight infections and eliminate waste products.  

White blood cells are an important part of the immune system, and special types of white blood cells are called to action when a cat is fighting an illness. 

When a cat is infected with feline leukemia virus, their white blood cells have been compromised and are no longer able to help fight off infections.  

Various skin, respiratory, and urinary infections can develop without a healthy immune system in place.  

The affected cat is unable to fight off these infections, leading to a shorter life span.  

The virus also causes mutations leading to cancer, including lymphoma and lymphosarcoma. 

Widespread vaccination has led to an overall decrease in leukemia cases; however, it remains a major disease in cats who frequent the outdoors. 

Symptoms of Feline Leukemia Virus

The most common clinical signs of feline leukemia virus are: 

• Pale gums 
• Decreased appetite 
• Weight loss 
• Poor coat (lack of grooming and dry/brittle fur) 
• Inflamed gums and mouth (gingivitis and stomatitis)  
• Fever 
• Enlarged lymph nodes 
• Chronic diarrhea 
• Chronic skin, eye, respiratory, or urinary tract infections (UTIs) 

Causes of Feline Leukemia Virus

The feline leukemia virus in cats is spread through saliva, though it’s also shed in the feces, urine, and milk. 

Close contact between cats, especially prolonged close contact, is the most common way FeLV spreads.  

Mutual grooming, mating, or shared food/water/litter boxes are examples of close contact that allows FeLV to spread between cats.  

It may also be spread by bite wounds or from a mother to her kittens through the placenta or through nursing. 

A cat at any age can be infected with feline leukemia virus through exposure.  

Allowing an unvaccinated cat to be unsupervised while outdoors may expose it to infected cats. Bringing a new cat into the home who has not tested negative for the feline leukemia virus may also spread the disease. 

Around 20-30% of exposed cats will have an effective immune response and clear the virus. This is called an abortive infection.  

These cats are considered immune to the disease and don’t usually test positive. They don’t spread the virus to other cats. 

Around 30-40% of exposed cats will have a partially effective immune response called a regressive infection. While an infection is regressive, it’s not contagious to other cats and doesn’t tend to cause symptoms. It can, however, reactivate later, causing symptoms and becoming contagious. 

Around 30-40% of exposed cats develop a progressive infection. These cats are at a high risk of developing severe infections and/or cancer, and they’re contagious to other cats. Kittens are more likely to develop progressive infections than adults. 

Fortunately, the virus is not very hardy in the environment and can only survive on surfaces for a couple of hours. This is why transmission usually occurs from direct contact between cats. 

Feline leukemia virus is not contagious to people or to other pets, like dogs or rabbits. 

How Veterinarians Diagnose Feline Leukemia Virus

Feline leukemia is usually diagnosed by a blood test called an ELISA test.  

This test is quick and routinely done in veterinary clinics. Your veterinarian may recommend repeating the test if they get a positive result, especially in young cats and kittens.  

Repeating the test eight to 12 weeks later helps to confirm if an infection is persistent. Some cat immune systems can eliminate the virus when they are first exposed.  

Feline leukemia virus undergoes several stages.  

In the first stage, infected cats show very little signs of disease as the virus enters their mouths and replicates on their tonsils.  

About 20 to 30% of exposed cats can eliminate the virus in this stage—if their immune system is healthy. This is an abortive infection. 

For the remaining two-thirds of exposed cats, the virus will spread to the lymph tissue and intestines. Around half of cats will develop regressive infections, where the virus will essentially go into hiding. During this time, the virus doesn’t usually cause symptoms and the cat isn’t usually infectious. The virus can later reactivate, becoming a progressive infection. Progressive infections lead to shedding of viral particles in the feces, milk, and urine in addition to the saliva. In advanced stages of the disease, it infects the bone marrow as well. 

Once the virus gets into the bone marrow, it cannot be cleared and these cats are infected for life. 

Your veterinarian may order additional testing that can determine if an infection is abortive, regressive, or progressive. 

Treatment of Feline Leukemia Virus

Unfortunately, feline leukemia virus does not have a cure.  

Affected cats are managed medically by treating any secondary infections that can result from the disease. Cats infected with feline leukemia virus often develop secondary skin, upper respiratory tract, eye, or urinary tract infections due to their immune system being compromised. 

Antibiotics may be prescribed to treat any secondary bacterial infections that may be present. 

Sometimes appetite stimulants or anti-inflammatory medications are prescribed in cats with leukemia who have a poor appetite or fever. Occasionally, blood transfusions may be recommended for continued quality life for cats with severe anemia. 

If your cat tests positive for feline leukemia virus, it is important to limit their exposure to secondary infections. It’s best that your cat remains indoors only and does not have access to other cats that may have contagious diseases.  

Any illness, no matter how small, is a threat to a compromised immune system. 

Recovery and Management of Feline Leukemia Virus

The average life span after testing positive for leukemia virus is less than three years. If your cat has feline leukemia and is allowed access to the outdoors, be sure it is under supervision.  

Some cats diagnosed with FeLV can live normal lives for years, especially if they are kept indoors with minimal exposure to secondary illnesses.  

If your cat enjoys the outdoors but you want to limit their exposure to the elements and other cats, consider a catio.  

Always avoid allowing shared food or water bowls and litter boxes between affected and non-affected (especially unvaccinated) cats to reduce risk of transmission. 

Management of a cat with feline leukemia may require frequent cleaning of the eyes and ears to keep them free of debris.  

Secondary skin, respiratory, eye, ear and urinary tract infections can be common in cats with compromised immune systems, so it’s helpful to keep them clean.  

Commercial ear cleaners, like Epi-Otic or EpiKlean, can be used to clean out any waxy debris in the ear canals.  

Eye washes can be helpful in keeping the eyes clear. 

Regular brushing will keep the skin and coat healthy.  

If you notice any signs of infection, schedule an appointment with your veterinarian immediately.  

Often, vets tend to be more proactive with antibiotics in a cat that has feline leukemia, since their immune system is typically suppressed by the virus. These cats are at a greater risk of developing severe bacterial infections. 

Prevention of Feline Leukemia Virus (FeLV)

You can reduce your cat’s risk of contracting feline leukemia with regular vaccinations.  

The American Association of Feline Practitioners recommends all kittens be vaccinated within their first year.  

Young kittens start the vaccine series at 8 weeks of age and receive a booster three to four weeks later. 

Cats who spend any time outdoors or who are exposed to potentially infected cats should continue regular vaccination each year, while low-risk, indoor-only cats may discontinue the vaccine after the initial series.  

Vaccinated cats will not test positive on the usual test performed in veterinary clinics, which is called a SNAP test. 

If a cat tests positive for feline leukemia, it should not be vaccinated against FeLV. Core vaccines like the rabies vaccine and FVRCP vaccine are still strongly recommended to protect the cat from dangerous infections.  

Any new cat should be tested for feline leukemia and FIV prior to being introduced to other cats in the household.