The Basics of FeLV in Cats: Everything You Need to Know

FeLV in cats is one of the most devastating infectious diseases that affect cats globally, and it’s the second most common cause of death among cats.

It manifests through inadequate immune response, leading to persistent infections, anemia, and, eventually, malignancies. 

FeLV primarily affects intact domestic cats, but other cats are also prone to the disease. Also, cancer is not the only cause of death among FeLV-positive felines – they often succumb to minor FeLV-induced infections as well. 

Nevertheless, feline leukemia in cats isn’t necessarily a death sentence. Cats may cope with secondary infections successfully and live relatively regular lives. Another good news is that FeLV is preventable, but the thing is, not all cat owners are aware of that. 

Therefore, we’ve researched the most critical FeLV facts and put them together for you.

What is FeLV in Cats?

FeLV is a retrovirus belonging to the family of oncoviruses along with other destructive viruses (such as feline sarcoma virus, mouse leukemia viruses, as well as some of the human viruses).

While the development of cancerous lesions is unquestionably one of the most severe FeLV consequences, it also results in other conditions such as repetitive infections, extreme neurological conditions, urinary system problems, etc.

The lifespan of the virus

Outside of the host organism, FeLV isn’t expected to survive for more than a couple of hours. Possibly, it will endure for two days under ideal conditions, but that is its topmost life span. Plus, just like any other virus, FeLV is highly vulnerable to heat and surfactants.

FeLV Transmission

Unlike FIV, the other dangerous feline virus with somewhat similar consequences, which can only be transmitted by entering the cat’s bloodstream, FeLV is spread easily.

In short, the transmission is possible through any form of physical contact. In other words, sexual contact is not needed for this to happen. The virus is spread through interactive activities, such as grooming, sharing food dishes, using the same litter box, etc.). 

Of course, FeLV in cats is unavoidably transmitted through aggressive contact such as biting. If a cat infected with FeLV gives birth to kittens, all of them will be affected as well.

Risk Factors

Cats that interact with the infected cats are at the most considerable risk of getting infected with FeLV. Out of all the cats that come in contact with the infection carriers, kittens and younger cats are most likely to contract it.

Of course, feral, strays, and pet cats allowed to wander around are the ones most exposed to the virus. This increases their risk of catching the virus, even though they have better chances of not getting it if they live in a single-cat household.

FeLV Symptoms

As previously mentioned, FeLV is a retrovirus. These are the viruses able to transform the genetic material of the infected cells and turn them into tiny virus workshops.

Such means of virus replication requires a significant amount of time, which is why infected cats may not show any symptoms at first. However, once they do, you will usually notice the following:

  • Appetite loss
  • Bad coat condition
  • Weight loss
  • Gingivitis and stomatitis
  • Persistent infections of the skin
  • Bladder issues
  • Recurrent fever
  • Weird behavior due to neurological changes
  • Eye diseases

Diagnosis: FeLV/FIV Test Types

There are different types of tests for diagnosing FeLV, which are also used for establishing the FIV diagnosis.

The most accurate diagnosis is based on the combination of anamnesis (including the information on the potential virus exposure) and one of the commonly used tests.

These are blood tests that will either determine the presence of the virus itself or its antibodies in the blood.


ELISA (standing for “enzyme-linked immunosorbent assay”) is the most basic FeLV-identifying test which can be performed during any visit to a local veterinary clinic.

In essence, it is a routine procedure conducted as an initial feline leukemia test. A positive ELISA is undoubtedly a sign of virus exposure, but it cannot pinpoint the exact infection stage.

Moreover, cats can test as false FeLV positive on ELISA if the organism is still in the phase of attempting to fight off the virus.


Due to the sophisticated technology required for performing it, IFA (IFA (standing for “immunofluorescent assay”) has to be done within a diagnostic laboratory.

These are blood samples of FeLV cats (as well as those with FIV) and are usually sent out from the local laboratory for further analysis. 

This takes place after a positive ELISA test to determine the exact stage of the infection (e.g., a positive IFA means that the virus has entered the bone marrow).

FeLV/FIV Combo test

For several years, an innovative way of testing FeLV and FIV at once has been used, called the Combo test. For performing this test, no commercial laboratory is needed – it can be conducted at your local veterinary clinic in no more than several minutes.

The only equipment required for performing this type of FeLV and FIV test consists of a piece of filter paper. Any changes on the paper after it comes into contact with blood drops indicate the virus’s presence or absence.

When to test kittens for FeLV/FIV?

There are no age-related limitations to taking tests for FIV and FeLV – a kitten may undergo the testing at any time.

However, the analysis does require taking some of the kitten’s blood. This may be challenging for the little ones (e.g., 5-week-old kittens), so it might be wiser to wait a few months before the test is taken.

If a kitten tested positive for feline leukemia, it usually has been infected with FeLV indeed, but this should be confirmed by re-taking the test. However, a negative test almost certainly means that the kitten has not been infected with FeLV.


FeLV is a highly destructive virus that causes the cat’s organism to be highly susceptible to various infections.

These infections are called secondary infections (FeLV infection being the primary one). They are responsible for most of the diseases in a cat infected with FeLV.

However, this does not occur overnight. There is a pattern of the disease progression, which is predictable to a certain extent.

Early stages vs. final stages

Roughly speaking, we can differentiate between early (asymptomatic) and final stages of feline leukemia (progressive deterioration of the cat’s health, usually starting with the loss of appetite and lethargy).


More specifically, based on the immune response after the initial FeLV exposure, there are three levels of the infection.

Abortive level

Seldom, a cat might get abortively infected, which means its immune system can respond to the infection effectively and completely eradicate it from the body.

Regressive level

In case of the regressive infection, a FeLV-positive cat is a virus carrier that has a quality of immune response that is high enough to clear the virus from the blood.

However, it is insufficient to remove its DNA from the bone marrow. The virus will eventually reactivate and trigger the symptoms. 

Progressive level

Once the infection reaches the progressive level, cats carry the tiny virus pieces in the blood. They are highly contagious to other cats, with severe symptoms of secondary infections.

Treatment of FeLV

Unfortunately, there is no cure for FeLV. The current possibilities are limited to the prevention and treatment of minor FeLV-induced symptoms (for instance, a FeLV cat will often get antibiotic prescriptions against bacterial infections or blood transfusions for alleviating the effects of anemia, etc.).

Still, there are certain things you should focus on.

Attention to nutrition

Nutrition is vital when it comes to treating the symptoms. It is a good idea to supply your cat with some of the immuno-boosters available on the market (do ask your veterinarian to recommend the best one).

To treat feline leukemia in cats, you should give your cat the essential nutrients, vitamins, and enzymes in a tasty form.

Foods to avoid

You should avoid feeding your cat meals that possibly contain bacteria, such as eggs and raw meat. Whenever you have some spare time, dedicate a little portion of it to preparing cooked meals for your cat – it will mean a lot.


First of all, make sure that all the new cats you adopt have undergone a FeLV test. If you happen to have a cat with FeLV sharing the home with healthy cats, take care of their bowls and litter box hygiene, and make sure that none of them are shared between the cats.


FeLV is highly preventable, but not completely. The reason is obvious – one cannot control a cat completely. Still, there are certain measures a responsible owner should consider.

Restricting the cat’s exposure to FeLV

FeLV transmission is possible during each healthy cat’s exposure to the potentially infected cats. With that said, make sure to keep your healthy cat away from the potentially infected cats.

It is highly recommended that the infected cat be neutered and kept indoors. If access to the outside world is allowed (we admit, it is cruel to completely devoid a cat of the freedom to explore its environment), provide a space with a secure enclosure.

Feline leukemia vaccine

FeLV vaccines have been available for many years and have dramatically decreased the incidence of FeLV.

However, while they certainly are efficient for preventing the spread of  FeLV and accordingly controlling the detrimental effects of it, they are not 100% reliable, as is the case with any other vaccine. 

Still, the experts highly recommend the FeLV vaccination for all kittens. As for adult cats, you have to make a sensible decision based on their lifestyle and potential exposure to the virus.

Potential FeLV Vaccine Side Effects

Minor allergic reactions to the vaccine are possible. FeLV vaccines have been formulated to be as harmless as possible. The side effects are highly unlikely (apart from mildly sluggish behavior immediately following the vaccination).

Since these usually happen immediately after the vaccination, a veterinarian will provide an efficient treatment right away. 

The vaccine is being constantly improved upon so that the risks are minimized. However, if you still have concerns over it, you might want to discuss things in detail with your veterinarian.


There are no rules when it comes to feline leukemia and life expectancy. Once a cat reaches the final stage of FeLV, it is most likely to live up to several months if cared for properly. 

Sometimes, a cat with FeLV will live for three to four years after being diagnosed with the virus. Statistics show that approximately 20% of cats with feline leukemia get to live over three years (though with an inevitably changed quality of life) after the diagnosis.

FeLV vs. FIV

  • Both FeLV and FIV belong to the same family of viruses, retroviruses. Still, FIV is a lentivirus, while FeLV is a gamma-retrovirus.
  • Both viruses are characterized by gradual progression, but FeLV will usually progress more quickly.
  • Both cause multiple secondary infections, but FeLV cats usually suffer from more severe illnesses such as cancer.
  • FeLV is transmitted during casual interaction between the cats. On the other hand, FIV has to enter another cat’s bloodstream to be transmitted.
  • While FeLV-positive cats must live in a single-cat household to prevent the spread, FIV cats can safely share a home with other cats.


How long do cats with FeLV live?

It depends on how well taken care of the cat is. Some cats get to live up to 15 years, like any other healthy cat. The life expectancy is heavily dependent on whether a cat gets infected as a kitten or as an adult. The virus is harsh on kittens, who mostly live up to 2 years.

Should a cat with feline leukemia be put down?

There is no need to get a cat euthanized because of the FeLV diagnosis. As long as your cat feels good, has an appetite, and has an overall sound quality of life, just keep doing whatever you can to prolong this, following the steps discussed in the treatment section.

How do you treat FeLV in cats?

Unfortunately, there is no cure for FeLV at the moment. However, there is a lot that you can do.

Regular veterinary care and undertaking the preventative measures that we’ve mentioned in the prevention section will undoubtedly help your cat feel good most of the time and fight off secondary infections if any appear.

Can FeLV-positive cats live with other cats?

No. Cats positive for FeLV virus actually require special treatment and environment. Other animals, such as bunnies or family dogs, can share the same household with FeLV-infected cats safely.

However, a cat with FeLV must not live with other felines that don’t have the disease since the virus is spread easily via shared bowls, litter boxes, etc.

What are the final stages of feline leukemia?

There are no actual “stages” of FeLV. Still, we can roughly differentiate between the initial and final phases, the latter of which is characterized by more severe symptoms.

As described in the progression section, once the disease reaches its final stage, apart from cats having severe symptoms, the infection becomes highly contagious.

What is the life expectancy of a cat with FIV?

Although FIV prognosis might be slightly better, the FIV-positive cats’ life spans are dependent on how the owners take care of them (as of those with FeLV). Both cats with FIV and cats with FeLV are likely to die sooner than an uninfected cat would.

As mentioned, a cat with FIV living up to 15 years is not an uncommon occurrence. Still, neither is a cat living for only five years after the diagnosis. 

Do indoor cats need a FeLV vaccine?

Not necessarily. The vaccine might not be beneficial at all for adult cats kept indoors. An owner should consult a vet to discuss the benefits and disadvantages of the vaccine based on its specific lifestyle, surroundings, and exposure to the virus.

Can feline leukemia be transmitted by fleas?

There haven’t been reports of cat diseases being transmitted to felines by insects, including fleas.

However, one of the older studies from 2003 examining the fleas that were fed for 24 hours with FeLV-infected blood has found that fleas might be potential carriers of the virus in vitro and possibly in vivo as well. However, we still lack modern-day evidence for the claim.

When should kittens be tested for FeLV?

Veterinarians say that there is no specific age at which kittens need to be tested for FIV and FeLV. Still, they should be tested in a timely manner when around six months old. Most kittens will test negative at first, which is not a completely reliable result.

What is the difference between FeLV and FIV?

Apart from being transmitted more easily, feline leukemia is usually more devastating than FIV. This is because FeLV often results in lymphoma, cancer of the bone marrow, or severe bone marrow suppression in very young cats. 

Still, the two viruses share some similarities, even though they are caused by different viruses. Both are contagious and most likely to affect cats that wander outside, and neither is curable.

What are the signs of feline leukemia?

There are no universal symptoms since some cats will not show any signs for years, and once they do, their symptoms probably won’t completely match the ones of other cats with FeLV. 

However, the most frequent symptoms are the following: enlarged lymph nodes, stomatitis, gum ulceration, heavy breathing, diarrhea, lethargy, fever, yellow color in the whites of eyes, bad fur quality, etc.

Can feline leukemia lay dormant?

Yes, the virus can lay dormant due to a lack of physiological stressors that would activate it again.

Can humans get FIV from cats?

No – neither FIV nor FeLV is contagious to people. They cannot even be transmitted to other animals.

How often should cats get the FeLV vaccine?

In kittens, the shots of vaccines are usually given in series every three to four weeks. Adult cats need shots less often, usually every year or every three years.


While having your cat diagnosed with FeLV is certainly heartbreaking news, try not to wallow in despair. You can undertake certain measures so that your cat’s life quality does not suffer.  

For a cat with FeLV, the life expectancy prognosis isn’t bright. Still, you can significantly postpone the final stage of the disease by adjusting its lifestyle and nutrition.

Other than that, make sure your cat is as comfortable as possible, and stay attentive towards it – we all know it’s what cats cherish the most. 

Hopefully, we have provided a broad insight into why prevention is of the utmost importance for cats’ health and what an individual owner can do to control the spread of FeLV in cats.

1 comment
  1. Like!! I blog frequently and I really thank you for your content. The article has truly peaked my interest.

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