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Key takeaways

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

  • FeLV is is transmissible between cats through contact with bodily fluids
  • 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
  • Symptoms of active FeLV infection include appetite loss, weight loss, poor coat condition, and chronic diarrhea
  • There is no cure for FeLV, so prevention is of the utmost importance
  • Treatment targets symptom management
  • Testing and vaccination are important tools for controlling this potentially lethal infectious disease
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A closer look: Feline Leukemia Virus (FeLV)

Many cats are carriers of FeLV. Infected adults usually do not exhibit symptoms during the first several weeks to years following infection.

In rare cases, cats may have a strong enough immune response to the virus to fully eliminate it. These cats never experience symptoms and cannot transmit the virus.

About 10% of cats exposed to FeLV have regressive infections, meaning that the virus is only partially cleared from the cat’s system. In this stage of infection, cats cannot transmit the virus. However, a regressive infection can become progressive at any time, and the cat then becomes a source of infection to other cats.

Between infection and the expression of 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. The disease progresses more quickly in kittens than in adults.

Once diagnosed with progressive FeLV, a cat has an average life expectancy of 2.5 years, even with aggressive treatment.

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Risk factors

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

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

Populations with the greatest risk factors include:

  • Cats with access to the outdoors
  • Cats that are not vaccinated against FeLV
  • Cats living in close contact with cats of unknown FeLV status

Possible causes

FeLV can be transmitted through casual contact between cats like mutual grooming, as well as through bites, and, more rarely, through sharing food dishes and litter boxes.

FeLV is is transmissible between cats through contact with 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 the virus.

Main symptoms

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 blood work and urinalysis to assess any symptoms they are presenting.

Steps to Recovery

Currently there is no cure for FeLV. Treatment is supportive and can include:

  • Antibiotics for secondary infections
  • Blood transfusions for anemia
  • Symptomatic treatment


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 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 Feline Leukemia Virus (FeLV) common?

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.


No Author - Writing for Cornell University College of Veterinary Medicine
Becky Lundgren, DVM - Writing for Veterinary Partner
No Author - Writing for American Association of Feline Practitioners

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