FirstVet
feline leukemia virus

Feline Leukemia Virus

Feline Leukemia Virus, or FeLV, is a retrovirus that infects felines only (domestic cats and some wild felids like cheetahs and the Florida panther). Feline Leukemia is the most common infectious disease of cats worldwide. Continue reading to learn more about this virus, how it’s transmitted, how it’s diagnosed, and how to protect your cat!

Are you concerned about your pet?

Book a video consultation with an experienced veterinarian within minutes.

Feline Leukemia Virus Transmission

FeLV is a retrovirus that is spread primarily in the saliva but is also present in blood, urine, feces, nasal secretions, and tears. Cats most commonly get infected by grooming one another, but bite wounds, sharing litter boxes and food/water bowls can also spread the infection. Queens (mother cats) can infect their kittens in utero through the placenta or after the kittens are born and are nursing.

Feline Leukemia Infection Stages

Many healthy cats that are exposed to the Feline Leukemia Virus can attack the virus and clear the infection before showing any signs of illness.

Other cats will have the virus spread to the lymph nodes, certain white blood cells, and even internal organs like the spleen, GI tract, and thymus, but still be able to kill the virus and clear the infection. These cats can spread the virus for 3 to 6 weeks as the immune system is trying to clear it.

If the cat was unable to clear the virus by now, it moves into the bone marrow and the cat won’t be able to fully clear the virus once it’s reached this stage. The virus will attack platelets and certain white blood cells and release those throughout the body.

Finally, the virus reaches the epithelial cells (top layer of cells). This stage is the riskiest time for virus transmission as so much of the virus is being shed into the urine, tears, and saliva.

Once a cat is infected, it can have a regressive infection and may not develop any clinical symptoms and live a normal life span. Other cats develop the progressive form of infection and develop an illness with a shortened life span of 2 to 3 years on average.

Diseases Caused By FeLV and Symptoms to Monitor For

  • Cancers, such as lymphoma, leukemia, fibrosarcoma, and osteosarcoma
  • Low red blood cells (anemia) causing weakness, pale gums, and organ dysfunction
  • Low platelets (thrombocytopenia) which can cause spontaneous bleeding or bruising
  • Low white blood cell counts leading to increased infection risk, especially to Feline Immune Deficiency Virus (FIV), Feline Infectious Peritonitis (FIP), upper respiratory tract infections (URI), and Mycoplasma infections
  • Immune-mediated diseases such as inflammation in the kidneys (glomerulonephritis), inflammation in the eyes (uveitis), inflammation in the joints (polyarthritis), and immune-mediated hemolytic anemia
  • Neurologic disorders if the diseased cells infiltrate the brain or spinal cord, which can lead to abnormal gait (movements), paralysis, abnormal behavior and vocalizations, abnormal pupil size, blindness, and even urinary incontinence (leaking urine)
  • Diarrhea, weight loss, vomiting, reduced appetite
  • Fading Kitten Syndrome
  • Fever
  • Enlarged lymph nodes
  • Severe gingivitis/stomatitis (oral inflammation)

How does my vet test my cat for Feline Leukemia Virus?

FeLV Antigen Tests are the primary screening test for cats. This test detects the viral antigens, which typically increase about 30 days post-exposure. If you just adopted a new cat or found a stray cat you decided to care for, you should get this test done twice, about 30 days apart, to avoid missing a recent infection. It’s also ideal to recheck this test in 30 days if your cat tested positive since they may be able to clear the infection in that time.

Antibody testing by IFA is another testing option. This test looks for infected blood cells and platelets. If this test is positive, it means the virus has infected the bone marrow. This test is helpful to confirm an infection if the antigen test is positive.

PCR testing is another testing option. It screens for viral RNA. This test can detect infections in some cats as early as 1 to 2 weeks post-exposure.

Routine blood work may show low red blood cells, low white blood cells, low platelets, and high globulins. These aren’t diagnostic for Feline Leukemia Virus, but they can give your vet needed information that screening for FeLV is necessary.

Is there a treatment for Feline Leukemia?

There are some antiviral and immunomodulation treatments available for feline leukemia; however, they are not cures. Cats can have severe side effects to many antiviral drugs, so be sure to discuss the pros and cons with your vet. The goal of these medications is to reduce clinical symptoms and increase survival times.

How can I protect my cat from Feline Leukemia?

Vaccinate your cat! The Feline Leukemia Virus vaccine should be given to all cats under a year old and new cats added to the home. The vaccine should be given once, then a booster 3 to 4 weeks later, then at the next annual visit, and possibly every 2 to 3 years thereafter. If your cat is indoors only and you aren’t planning to adopt or foster any other cats, you may only need to get your cat the initial series of vaccines. If your cat is outdoor only, indoor/outdoor, or you will be adopting or fostering other cats in the home, you should keep your cat current on the Leukemia vaccine.

If your cat does test positive for Feline Leukemia and the test has been confirmed, keep your kitty indoors to deter the further spread of the virus in the community. This will also keep your cat safer and healthier since they won’t be exposed to other viruses and infections.

Read more:

What You Need to Know About Vaccinating Your Cat

Have more questions about Feline Leukemia Virus?

Schedule a video consult to speak to one of our vets.

Are you concerned about your pet?

Book a video consultation with an experienced veterinarian within minutes.

Book Video Consultation
  • Low-cost video vet consultations, 24 hours a day
  • Experienced, licensed vets
  • Over 500,000 satisfied pet owners

More articles about Cat