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Feline Leukemia: Treatment, Signs, and Testing
Updated on January 4, 2023
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Feline Leukemia: Treatment, Signs, and Testing

FeLV (Feline Leukemia Virus) is a retrovirus that usually carries a grave prognosis for cats.

It is one of the most common causes of death for the species. About 85% of all infected felines die within three years of diagnosis.

While a small number of infected cats may survive the illness, they must often live with it for the rest of their lives.

Feline Leukemia: Treatment, Signs, and Testing 2

Clinical signs of Feline Leukemia virus

FeLV has several adverse effects on a cat's body. It is a leading cause of cancer and may often result in various blood disorders.

It also commonly leads to a state of immune deficiency in which the cat loses its ability to fight off infections. The cat’s immune system fails to function.

As a result, common viruses, bacteria, fungi, and protozoa that usually do not infect cats can cause significant illness. These secondary infections are the primary cause of the many diseases attributed to FeLV.

During the early stages of infection, cats may not exhibit any signs of disease. However, over time, a cat's health will steadily decline. This may take a few weeks, months, or even years. Sometimes, the cat will start to experience repeat cycles of illness.

Cats with FeLV may exhibit the following symptoms:

  • Progressive weight loss
  • Loss of appetite
  • Enlarged lymph nodes
  • Poor coat condition
  • persistent fever
  • chronic diarrhea
  • pale gums and other mucous membranes
  • abortion of kittens and other reproductive complications
  • behavior changes, seizures, and other neurological conditions

The Dangers of FeLV

FeLV infected cats are more prone to developing other health disorders such as:

  • Anemia (low red blood cell count)
  • Cancer
  • Immunosuppression which puts the cat at risk for other infections
  • Inflammation in the intestines
  • Neurologic disorders such as blindness and nerve dysfunction
  • Reproductive issues such as “fading kitten” syndrome and loss of pregnancy
  • Stomatitis (severe inflammation in the mouth)

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How FeLV spreads

FeLV spreads through:

  • mutual grooming
  • bite wounds
  • blood transfusions

It may also spread when infected mothers nurse their kittens. 

Adult cats with healthy immune systems have a greater chance of surviving the infection than kittens (who have underdeveloped immune systems) or immune-compromised adult cats.

Since it is so infectious, it is not unusual for cats found positive to be euthanized by shelters. Often, they are rejected by transfer programs due to poor prognosis and significant risk of transmission.

FeLV tests

FeLV testing can be challenging due to the various stages and infection forms this disease can exhibit.

Most studies site a regressive and progressive disease form. 

The progressive form is also described as the persistent form. It is when the virus cells are proactively replicated by the body and released. Animals with this variation of the disease will likely develop leukemia virus symptoms. They may die from associated complications.

The recessive/latent infection is when the immune system actively fights off the infection and halts the disease's progression. These animals are less likely to die but will still spread the disease. It is commonly believed that the two forms of the disease may switch back and forth. This complicates the diagnosis and management process.

ELISA (enzyme-linked immunosorbent assay) tests are a great way to detect FeLV. This is because they are not affected by animal vaccination status. However, testing is complicated by the possibility that the animals could fight the infection or develop a latent infection. This means that the test would work only at a specific point in time.

A negative test does not satisfyingly rule out the possibility of infection. It depends on where the cat may have been exposed. Similarly, a positive test does not mean the cat will be persistently infected and die from the disease. Antibodies may still circulate in the cat's blood long after the cat has fought the infection.

For these reasons, it's advised to carry out an immunofluorescent assay (IFA) laboratory test. This is to confirm the findings of an ELISA test. 

Several studies have shown that about 33% of all positive in-house ELISA tests provided false results. IFA tests are a reliable indicator of viral replication or an actual infection. ELISA tests, on the other hand, can only show exposure and disease development potential.

Feline leukemia virus treatment

Unfortunately, 85% of all cats with a persistent FeLV infection die within three years of diagnosis.

However, frequent trips to the vet, along with effective management, helps. Doing so can help cats feel well for a considerable period and help protect them from secondary infections. 

There are drugs that have shown great potential for use against feline leukemia virus infection for the treatment of FeLV-positive cats. Studies have been conducted to test their efficacy.

If your cat has been diagnosed with FeLV, you should take it to the vet twice a year.

This is for laboratory testing, physical examination, and parasite control. This will help your vet identify problems quickly and prevent complications. All cats infected with FeLV should be neutered and kept indoors.

Is there a vaccine for FELV?

There are two types of vaccines available. The first is an adjuvanted killed virus. The second one is a nonadjuvanted recombinant infectious vaccine. However, none of these offer complete protection.

Note: FeLV vaccines are generally avoided because of their potential to cause cancerous tumors (sarcomas).

Sarcomas are aggressive, cancerous growths that require invasive procedures to remove. However, the tumors usually can’t be removed and prove fatal. For this reason, your veterinarian may advise you not to give your cat the vaccine.

The vaccines are recommended for cats at high risk of infection, such as:

  • Those with outdoors access
  • feral cats
  • Uninfected cats who live with an infected cat
  • cats in multi-cat households
  • cats whose status are not known (living in animal shelters or similar facilities)

How do I protect my cat from FELV

There is no known cure for FeLV. The only guaranteed way to protect your cat is to limit their exposure to FeLV-positive cats. Keeping your cat indoors, for example, will prevent contact with potential carriers. 

If you wish to take your cat outside, provide adequate supervision. You may also place them in a secure closed environment to avoid fighting and wandering.

All cats should be tested for FeLV before you bring them into your home. Healthy cats should be separated from those who've been infected, regardless of whether they show symptoms. They also shouldn’t share litter boxes and food and water bowls.

Unfortunately, most owners will not realize their cats have the condition until they have lived with other cats. In such situations, all cats in the household should be tested for FeLV.


While a FELV diagnosis can be disheartening, it is essential to remember that cats with this condition can live happy, relatively normal lives for significant periods. 

If your cat has been diagnosed with the illness, there is something you can do.

Carefully monitor appetite, weight, activity level, and behavior.

Doing so will help you give your cat appropriate care and manage the disease.

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Updated on January 4, 2023
Dr. Alam
Dr. Alam Roky
Medical Reviewer
Dr. Shamsul Alam Roky is a registered veterinarian who graduated from the Faculty of Veterinary, Animal, and Biomedical Sciences. Currently, he is working as a graduate research assistant at his university, in addition to running a private veterinary clinic named ‘Sylhet Veterinary Services” in his city.
Joel Hirsch
Joel Hirsch
Content Contributor
Joel Hirsch is a health enthusiast and gym rat with a degree in Health Sciences. He spends his time writing about products that help people reach their health goals.
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