Feline Leukemia Virus And Its Effects on Cats And Kittens

Feline Leukemia Virus

What is Feline Leukemia Virus (FeLV)?

Feline leukemia Virus is not cancer of the blood, as in Leukemia diagnosed in humans. Rather, it is regarded as a ‘retrovirus’ due to its similarities to other retroviruses within the cells that are infected. It falls in the same category as FIV -feline immunodeficiency diseases, and includes HIV – the human immunodeficiency virus. 

These two viruses, though genetically different, generate an enzyme termed reverse transcriptase. This enzyme allows a process whereby it inserts copies of its genetic matter into the infected cells of the host.

Transmission of the Virus

Feline leukemia Virus

This disease is fortunately not transmitted to humans, dogs, or other species. The disease is only associated with cats. It is viral infection of cats that affects the cat’s immune system and bone marrow. The virus is contracted by cats that come into contact with other cats. It is mostly spread through bodily fluids and can live outside of the body only for a brief period.

Statistics of cats infected with the Feline Leukemia Virus

A very low 2-3% of cats in the USA are infected with FeLV even though the virus is prevalent worldwide. The statistics can rise drastically to as high as 13%, influenced by factors such as age, physical health environment, and lifestyle, i.e.

  • Very young cats and kittens that do not have well-developed immune systems are at high risk,
  • A weakened immune system and recurring bouts of illnesses, 
  • Living in a cattery or shelter and in constant contact with other cats,
  • Cats that are mostly outdoors and could get into fights with other cats.

Kittens born with the Feline Leukemia Virus

The FeLV can be transmitted from the mother (queen) to her kittens in utero. It can also spread from the mother to her nursing kittens as well as during ‘grooming’ sessions. It can be a dangerous situation for kittens infected with the virus. 

Feline Leukemia infects mostly kittens under four months old. In some cases, the virus was naturally dispelled from the kittens’ bodies, and they never became ill. Kittens that test positive are permanently infected as there is no cure for the virus. However, they may not show signs of infection for several years. 

Testing for FeLV

A queen and her whole litter must be tested for the virus. New-born kittens, however, still have maternal antibodies circulating in their immune system. These antibodies, unfortunately, interfere with the accuracy of the test.

If a queen and even one kitten test positive for the virus, the whole litter should be isolated until the follow-up tests. Kittens need to be re-tested after 5-6 months when the maternal antibodies are out of their system. 

The different stages of infection with the Feline Leukemia Virus

The presence of viruses in the blood is termed viremia. There are two distinct stages of progression after being infected with the virus.

Primary viremia

This is the early stage of the infection. Interestingly, some cats overcome this stage naturally thanks to a strong, healthy immune system. The cat’s immune system can eliminate the virus on its own, end of a potentially sad story!

Secondary viremia

This occurs at a later stage after the virus has entered the cat’s body. The cat’s bone marrow and other organs are constantly under attack with infections. It is a stage of ‘no return’ as the cat will remain permanently infected throughout its lifetime.

The Process of managing FeLV

Diagnosing the virus

Symptoms of infection

Life expectancy after being diagnosed

Prevention of infection with the virus

Initially, a primary blood test namely *ELISA can detect FeLV proteins which can indicate the presence of the virus

It can detect both primary and secondary stage infections.

Most often no physical symptoms exhibited when a cat is infected in early stages.

The virus can remain in the cat’s bone marrow for some time, even years before becoming active.

At this stage, the cat’s immune system, if strong enough, could attack the virus and destroy it. This gives the cat life-long immunity to FeLV.

Kittens have very little chance of survival due to their underdeveloped immune system

Vaccination of kittens and cats that have been tested negative for the virus is highly recommended.

The vaccine is recommended by the ‘American Association of Feline Practitioners’ who also provide guidelines for administering the vaccine.

The advanced stage of the infection is determined In a second blood test named *IFA

This test cannot be performed at a veterinary clinic, only in a laboratory.

The suppression of the immune system leads to the cat being susceptible to all types of bacterial and viral infections.

Symptoms may include:

  • Weight loss and/or loss of appetite

  • Pale gums

  • Yellow color in the mouth and whites of eyes.

  • Bladder, skin, or ear infections

  • Persistent diarrhea.

  • Enlarged lymph nodes

  • The poor condition of its coat.

  • Weakness and listlessness

  • Fever (not always)

  • Wobbly, unsteady movement.

Feline Leukemia Virus is the second most prolific cause of death to cats.

Statistics have shown that 85% of cats that are permanently infected with the virus do not live beyond three years after the diagnosis.

Case studies have shown that if cats are diagnosed as adults, they could live up to 15 years after diagnosis.

(this is possibly due to genetic strength and a healthy, well developed immune system)

Kitten and Cat Vaccination Schedules against the Feline Leukemia Virus

Kitten and cat vaccinations prevent the gestation and transmission of various deadly feline diseases. The Drake Centre for Veterinary Care is emphatic about the absolute importance of vaccinations to the overall well-being and longevity of your cat.

All cat owners should familiarise themselves with the guidelines provided by the Association of Feline Practitioners (USA) concerning the vaccination of cats and kittens. They created this guideline based on the existing published data. Furthermore, a group of veterinary experts from various disciplines in the field convened to share their extensive knowledge and expertise on feline infectious diseases. These practical guidelines are a great help to veterinarians to select the best options in vaccination schedules for their feline clients.

Vaccinations for Kittens

A new kitten joining the family should be seen by a veterinarian as soon as possible, regardless of age. This visit would serve as a general medical examination and schedule an appointment to be inoculated against FeLV. However, several factors will influence the need for your kitten to be vaccinated. These factors need to be discussed with the veterinarian.

Feline medical experts recommend that kittens should receive their first vaccination against Feline Leukemia Virus at eight weeks of age. A second dose should be administered three to four weeks later.

Adults and kittens over 16 weeks of age that are vaccinated for the very first time should receive two doses, three to four weeks apart. Veterinarians advise an annual dose of the vaccine for cats diagnosed with sustained exposure to the virus.

Side Effects and risk factors to the FeLV vaccine

Unfortunately, no vaccine has ever been 100% effective. The FeLV vaccine is between 75 to 85 percent effective to dateWe must remember that an inactive strain of a virus is being injected into the cat. This initiates a new process for the cat’s immune system to develop antibodies.

Some cats experience side effects and adverse reactions to the injected antiserum. This could be due to pre-existing genetic and medical conditions. A compromised immune system or an allergic response to certain agents contained in the antiserum itself is another possibility.

The development of ‘Sarcoma’ associated with the FeLV vaccine

An uncommon strain of a cancerous tumor known as ‘sarcoma‘ has been linked to the FeLV and some other vaccines. According to the Cornell University of Veterinary Medicine, this is a controversial issue. Investigative research is continuously being conducted to understand and determine the impact the various vaccines against infectious viral diseases may have on cats developing sarcomas.

Feline vaccines have been specifically developed and play a vital role in the battle to prevent and contain the Feline Leukemia Virus and similar deadly feline infectious diseases. Although these vaccines have been on the market for many years, continuous research is being conducted to improve its overall efficacy.

In the end, the rewards and benefits of feline vaccinations far outweigh any associated risks.

Methods to prevent cats from contracting FeLV

  • The first and most obvious rule is to keep your cat indoors and supervised outdoor visits.
  • There is a multitude of feline infectious diseases around. It is best to keep your cat indoors to reduce the chances of it becoming infected.
  • Feline Leukemia is commonly contracted from cats that socialize with infected cats, mostly outdoors. Because the virus is spread through bodily fluids, catfights, and grooming among cats become a potential risk factor. 
  • Between two and eight percent of cats that have free-reign outside, regardless of geographic location, are tested positive for FeLV.
  • When cats have not been in contact with other cats, the chances are good that they are not infected with the virus. If that is the case, please do not feel obligated to have your cat vaccinated.
  • If a cat is adopted from any feline institution or private owners, it is essential to vaccinate your present cat/s living in your home.

There has been a radical decline in recorded cases of FeLV in the past few decades. This reduction in the spread of the virus is good news indeed for cat lovers. Contributing factors may include:

  • Screening tests are readily available and have become more accurate,
  • Campaigns have been initiated to educate the public of the spread of FeLV,
  • Advice and methods to prevent cats from contracting the virus communicated veterinarian clinics,
  • Cat owners taking responsibility for their cats’ health and wellness,
  • Cats are enticed by various toys and gadgets, to enjoy their time indoors rather than the big wide outdoors with all the risks involved,
  • Cats that are regarded as at risk of contracting the virus are being vaccinated timeously.

The Important role of balanced nutrition

In addition to keeping your cat indoors, it is equally important to feed it a well-balanced, low-toxin diet. It will help to boost your cat’s immunity. Most adult cats (1-6yrs) need 35-40% protein in their diet. Wet food is said to have higher protein content than dry food. Food must be grain-free as cats don’t digest grain very well. 

Obtain advice on cat diets that offer an excellent, well-rounded approach to nutrition. 

Purina salmon cat food dry is a grain-free, protein-rich, balanced cat food. Read up on nutritional supplements. Cat vitamins are specifically designed to correct nutritional deficiencies in a cat’s diet. An excellent supplement choice is pet naturals” which contains twenty health-building ingredients. Improving your cat’s diet and nutritional intake is an investment in your cat’s longevity.

Treatment for cats that have contracted the Feline Leukemia Virus

No cure has yet been found for cats infected with FeLV. Statistics show that 85% of cats that are permanently infected with the virus don’t live beyond three years after being diagnosed.

It is difficult to anticipate secondary infections. Hence it can only receive treatment once it manifests.

Veterinarians use Chemotherapy to treat cats with cancer. However, cats diagnosed with widespread lymphoma and disease of the bone marrow, unfortunately, do not have a chance of survival.

The virus is fatal for kittens that test positive as their immune system is not strong enough to deal with it.

Cat owners should take precautions to ensure your cat maintains the best possible health regime. Regular visits to the veterinarian are critical at this stage of your cat’s life. Your cat will have a better quality of life, and it may help protect it from further infections and trauma. 

Try to have your cat examined twice a year by a veterinarian is an essential part of the process. This can prevent further complications. Veterinary experts agree that cats with infection should not be allowed to go outdoors so that they cant interact with other cats. It is also recommended that males be neutered.


It is clear that when it comes to life-threatening viruses, prevention is the most important action that you can take to ensure your cat’s all-round health and wellness.