Leukemia in Cats (FELV), Symptoms, Diagnosis, Treatment, Vaccine

Leukemia in cats is also known as Feline leukemia virus (FELV) is a retrovirus infection that affects cat’s “mostly kittens,” leading to diseases like Anemia or cancers like Lymphoma. It also suppresses the cat’s immune system eventually leaving the cat vulnerable to other disease-causing infections.

Usually, affects cats with weak or not well developed immune systems which are mostly kittens younger than four months old or ill cats; when a cat is sick infection possibility increases by 30%.

Fortunately, healthy cat’s immune system can fight off the infection at a 70 % resistance and elimination rate for healthy FELV exposed cats.

Leukemia in Cats
Leukemia in Cats

As a cousin to FIV (Feline Immunodeficiency Virus) there are lots of similarity between the two, however, FELV is a bit more dangerous because its fatal rate is very high, making it the most common cause of disease in felines and second to trauma “accident” in causing death in cats.

Cause of FELV and Mode of Transmission

FELV is due by a retrovirus which usually presides in infected host nasal secretions, saliva, feces, urine or milk; all through an infected cat’s body secretions. For FELV to be transmitted it has to go through the body secretions, so the mode of transmission which occurs from cat to cat becomes possible when your uninfected cat has prolonged interplay and contact with an infected cat.

The most common of all is saliva i.e. bite from an infected host, however here are the other typical activities that can lead to transmission

  • Grooming
  • Licking
  • Biting
  • Sharing dishes
  • Blood transfusion from infected cat
  • Sharing litter pans
  • During pregnancy, while giving birth or when nursing “breastfeeding” from an infected mother; either through the placenta before birth, or through their mother saliva or milk.

The virus doesn’t survive for long when it’s outside the cat’s body just like FIV. FELV Infection is more common in wild cats; because of prolonged contact or interaction with other cats plus frequent fights between them, whether it’s for food or shelter. FELV resistance usually rises with age, but it still can affect adult cats. Remember that it only be transmitted from cat to cat.

Signs of Leukemia in Cats

When it comes to symptoms, FELV doesn’t have specific symptoms that classify it; what makes the difference in the state of the symptoms usually deepens on the progress of infection and the cells affected. In the early stages, the pet will have no signs but later on the signs will be more apparent and also severe; plus FELV associated diseases will arise, some of them as signs and others will cause more symptoms to occur.

Here are some minor symptoms brought on by FELV:

  • Fever
  • Bad breath
  • Behavioral change
  • Runny eye or nose
  • Loss of appetite
  • Lethargy
  • Weight loss
  • Vomiting
  • Less grooming
  • Pale gums and other mucous membranes
  • Sleepiness
  • Fatigue

Here are vital signs of FELV:

  • Persistence intermittent diarrhea
  • Enlarged lymph nodes
  • Seizures
  • Anemia
  • The third eyelid extended further than usual
  • Uneven pupils (anisocoria)
  • Weight loss
  • Gingivitis of the gums and mouth (stomatitis)
  • Infections of the skin
  • Infection of respiratory tract and urinary bladder
  • Lymphoma “the most common cancer caused by FELV
  • Oral disease,
  • Neurological problems

Leukemia, Lymphomas, and Non-regenerative Anemia’s are the fatal diseases brought on by FELV.

The clinical signs might be confusing when compared with many other diseases or might be a result of certain diseases like liver disease, feline hyperthyroidism, kidney disease, and hyperthyroidism, so in order to fully conclude that your cat has the virus he/she must get FELV tests. Asymptomatic carriers will show no signs of disease, often for many years.

Stages/ Progression

The whole process from infection to the cut being able to infect other cats takes about 2-6 weeks which depends on the cat’s immune system and level of resistance.

  • After entering the cat’s body, the virus infects the macrophages and B-lymphocytes and later replicates in the lymphatic tissue.
  • The virus then spreads into the blood stream usually in the white blood cells circulating in the cat’s body.
  • The third stage is where the lymphoid system is attacked specifically the lymph nodes. 70% of cats can fight off the infections at this juncture because the immune system makes antibodies that prevent further replication of FELV.
  • In this stage, if the immune system doesn’t fight off the virus, FELV starts taking over the immune system, spreads to the born marrow, causes viremia, and infects the intestines and haemo-lymphatic system. It is the main stage of infection, and where then the virus remains in the bone marrow forever.
  • Here the cat can’t is officially infected with FELV, where it’s replicated in the white blood cells produced by the bone marrow.
  • In this last stage is the virus is shed to the cat’s body secretions “nasal secretions, saliva, feces, urine or milk.”

There are common effects of progressive FELV

  • Immunosuppression- occurs 50% of cats leukemia related diseases
  • Anemia –occurs 25% of cats leukemia related diseases
  • Damage to DNA usually leads to cancer- occurs in 15 percent of the cases. Cats with FELV have an increased 50% chance of getting cancer than a cat free from FELV.


American Association of Feline Practitioners (AAFP) recommends for testing of FELV in cats to help manage this infection. Here are other reasons you should take cats for testing other than clinical signs:

  • When your cat came into contact with an infected cat
  • When a kitten is entering into new household
  • Should be tested twice yearly regardless of its status
  • Should be tested before vaccination “the good thing is that vaccination doesn’t interfere with the tests for FELV.”

Tests Done

There are two tests commonly used to verify for FELV in cats that give accurate results; they include ELISA and IFA blood test done by the vet

  • Index snap test (ELISA blood test) is the first taste performed. It detects FELV proteins in the cat’s blood even in early stages of infection and only takes a few minutes to get results.
  • If the test results are positive for FELV, then the vet sends a blood sample for an IFA The test helps determine the stage of FELV infection and also help confirm ELISA positive results.
  • There is some blood cell and blood chemistry test done to see the damage extent brought about by the virus.

When the ELISA results are Negative, it may mean that your cat has not been exposed to the virus or if they were exposed they conquered FELV, or maybe they were exposed to FELV, but it’s too early for it to appear in the test.

When the cat tests Positive it may mean that FELV is its early stages, so the cat’s immune system has still got a chance to resist and eradicate the various from the body; that’s why IFA blood test is needed. Secondly, it might become a carrier of the virus meaning the virus won’t affect it. Finally, it might overcome the cat leading to various diseases and eventually death.

The kittens sometimes show negative results even when it has FELV, and this could go on for months after infection that’s why the test is done again when the kitten reaches six months of age to have a definitive diagnosis fully. And even if your cat test positive or negative it should be retested 60 days later.

Treatment of Leukemia in Cats

There is No cure or treatment for FELV, what vets do is give out management tips and some drugs that can help with the situation depending on the stage of infection, clinical signs and the effects of the virus on the cat’s body.


  • Should receive regular checkups from the vets to prevent further damage and manage stages of FELV.
  • Blood transfusion
  • Drugs to help with anemia e.g. Anabolic Steroids
  • Appetite Stimulants drugs to help with appetite
  • Avoid food that carries health risk “raw food.”
  • Interferon- Studies suggest that it has clinical benefits.
  • Good quality nutrition
  • Chemotherapy to manage cancer brought on by FELV. Cortisone also helps reduce tumor sizes.
  • Vitamin supplements can also help
  • Antibiotics drugs help with secondary bacterial infection

This management plan helps a lot especially the immune system in fighting off FELV when it’s in its early stages.

Cost of Management of Leukemia in Cats

The cost depends on your living standards and severity of the case in most occasions it ranges from $300 to $1200.

Facts about Leukemia in Cats

  • FELV vaccination don’t interfere with the test which is a case seen with FIV vaccines and vaccination is not protective
  • A third of cancer in cats is a result of FELV caused tumors.
  • Cats cat infect other animals including humans with the virus.
  • All cats breeds can get the virus and
  • Infected mothers usually don’t
  • The infection rate is at 1-2% in healthy indoor cats
  • Kittens less than for months are at a high risk of infection because they are susceptible to FELV, this is not the same for older cats who are highly resistant to FELV.
  • 85% of FELV positive cats die within three years even with treatment and management plans.
  • Male and outdoor cats are also at a higher risk of getting FELV
  • FELV infected cats range from 3-4% around the globe.


To avoid you cat from getting FELV or infecting other cats if he/she is FELV positive there are several precautions you should take.

  • Your cat should be tested for FELV and should receive regular checkups from the vet.
  • FELV positive cats should be well looked after and kept at a safe distance away from other cats to prevent FELV spread; they shouldn’t be allowed to roam around.
  • FELV positive cats should be allowed to breed
  • Don’t let your cat go most of the time outdoors and or let them interact with wild cats, to limit exposure to FELV infected cats.


It’s not totally effective in all cases but somehow necessary in helping prevent FELV. The vaccine can’t help already infected cats. All FELV vaccines have been tested and are okay to use and are available as combination vaccines.

There is a recommendation by the AAFP for all kittens to be vaccinated and also including adult cats. Kittens are vaccinated against FELV; just around when they are 8-9 weeks old and booster vaccines are given 4 weeks later.

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