Feline Leukemia Virus (FeLV)


Feline leukemia virus (FeLV) is one of the most prevalent infectious diseases and is the most common cause of cancer in cats. 

Some cats are able to fully eliminate the virus, while other cats remain relatively symptom-free for weeks to years following infection.

Symptomatic cats in the progressive phase of the illness have a life expectancy of 2.5 years following diagnosis.  

There is no treatment for FeLV, so prevention is of the utmost importance. Testing and vaccination protocols are important tools for controlling this potentially lethal infectious disease.

Risk Factors

FeLV is is transmissible between cats through contact with multiple bodily fluids including: 

• Saliva • Blood • Urine • Feces • Mother’s milk • Nasal secretions

Transmission of FeLV from mother cats to their kittens either in utero or while nursing is a serious concern because a kitten’s immature immune system is poorly suited for fighting off the virus. FeLV is highly contagious, incurable, and potentially fatal. It is a bigger concern for: 

• Any new cat or kitten prior to entering the household • Cats who go outside

• Cats who are not vaccinated against FeLV • Cats who live in close contact with cats of unknown FeLV status

Possible Causes

FeLV is caused by infection by the feline leukemia virus. FeLV can be transmitted through casual contact between cats like mutual grooming or sharing food dishes and litterboxes.

Main Symptoms

The primary symptoms of FeLV, when they are present at all, include: 

• Loss of appetite  • Weight loss  • Poor coat condition  • Chronic diarrhea

FeLV is also suspected in cats who experience frequent or recurrent: 

Upper respiratory tract infections • Skin infections • Urinary tract infections • Gingivitis and oral infections

Detailed Characterization

Many cats are carriers of FeLV. Infected adults usually do not exhibit symptoms during the first several weeks to years following infection. Some cats have a strong enough immune response and fully eliminate it the virus. These cats never experience symptoms and cannot transmit the virus.  

Cats infected with FeLV may develop a number of secondary conditions including:

• Anemia • Immune-mediated disease • Suppression of the immune system • Cancer

Between the time of infection and the expression of the symptoms, the cat remains healthy and leads a normal life. The duration of time between infection and onset of symptoms varies widely from weeks to years.

Once diagnosed with progressive FeLV, a cat has an average life expectancy of 2.5 years, even with aggressive treatment. The disease progresses faster in kittens than in adults.

Testing and Diagnosis

FeLV is diagnosed with two specific blood tests:  the enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescent antibody assay (IFA). If  a blood sample from an ELISA-positive cat also tests positive on IFA, the cat is likely to remain FeLV-positive for life.

In addition to FeLV-specific testing, a cat suspected of having FeLV will likely undergo routine bloodwork and urinalysis to assess any other symptoms they are presenting.

Steps to Recovery

Currently there is no cure for FeLV. Treatment is mainly supportive and often includes:

• Antibiotics for infections caused by the cat’s weakened immune system 

• Blood transfusions for anemia


The most effective way to prevent FeLV infection is to avoid  contact between infected and non-infected cats. 

The FeLV vaccine is an important tool for preventing the disease. Vaccination is recommended for all kittens and new cats who test negative, and boosters are advised for cats living at higher risk for acquiring the infection. Ensuring that a cat is not exposed to the virus is the only certain way of fully protecting the cat, as the current vaccine is not 100% effective.

FeLV screening blood tests are recommended for all new cats or kittens upon introduction to a new household. Vaccination is recommended for most negative cats.

Is FeLV Common in Cats?

FeLV is one of the most common infectious diseases in cats, but it is rare, affecting only 2-3% of the entire feline population. Infection rates can reach as high as 30% in high-risk populations.

Typical Treatment

There is no cure for FeLV, but treatment of the secondary conditions associated with it may include antibiotics and blood transfusion.

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