Few diagnoses worry cat owners more than a positive feline leukemia test. The name alone sounds like a verdict. But FeLV is more complicated — and more hopeful — than its reputation suggests. Some infected cats clear the virus entirely. Others carry it silently for years. And the cats most at risk are often the ones we can protect most easily, through a few simple decisions about testing, vaccination, and how cats share space. Here is what veterinary science actually knows about feline leukemia virus, and what a positive result really means.

What FeLV Is

Feline leukemia virus is a retrovirus — a virus that inserts a copy of its own genetic code into the cat's DNA. That ability to embed itself is what makes FeLV so persistent, and it is also why the virus can do so much more than cause leukemia. Despite the name, the most common consequences of FeLV infection are not cancers at all but immune suppression and anemia. By weakening the immune system, FeLV leaves a cat vulnerable to a long list of secondary infections that a healthy cat would shrug off.

According to the Cornell Feline Health Center, FeLV is one of the most common infectious causes of death in domestic cats worldwide. It is also species-specific: FeLV infects cats, not humans, dogs, or other household animals. You cannot catch it from your cat, and your dog cannot either.

How It Spreads

FeLV is shed primarily in saliva, but also in nasal secretions, urine, feces, and the milk of an infected mother cat. The virus is fragile and does not survive long outside the body, which means transmission almost always requires close, prolonged, cat-to-cat contact rather than a fleeting encounter. The most common routes are:

That last point is one of the most important in all of feline medicine: susceptibility drops sharply with age. Kittens and young cats are far more likely to become persistently infected after exposure, while many healthy adult cats mount an immune response that contains or eliminates the virus. This is why a single brief exposure rarely infects an adult indoor cat, and why outdoor kittens are the highest-risk group of all.

Progressive vs. Regressive Infection

Here is the part that changes how owners should think about a diagnosis. Exposure to FeLV does not lead to one fixed outcome. Veterinary research, summarized in the 2020 AAFP Feline Retrovirus Testing and Management Guidelines, describes several distinct paths the infection can take. Roughly speaking, after exposure:

This distinction matters enormously, because the prognosis and the management plan are completely different depending on which category a cat falls into. It also explains why veterinarians retest rather than acting on a single result — a positive test in a recently exposed cat may not be permanent.

Symptoms to Watch For

In the early stage of infection, many cats show no signs at all. As the disease progresses — particularly in progressively infected cats — owners may notice a slow, nonspecific decline that reflects the virus's effect on the immune system and bone marrow. Signs commonly associated with FeLV include:

Because the virus suppresses immunity, many of the illnesses that ultimately harm an FeLV-positive cat are secondary infections rather than the virus directly. FeLV is also strongly associated with certain cancers, most notably lymphoma. None of these signs are unique to FeLV, which is exactly why testing is the only way to know.

Testing and Diagnosis

Diagnosis usually starts with a quick point-of-care blood test that detects FeLV p27 antigen, a viral protein. These tests are sensitive and can be run in the clinic in minutes on a few drops of blood. The AAFP recommends knowing the retrovirus status of every cat, and testing is especially important before introducing a new cat to a household, after a possible exposure, or whenever a cat becomes unexplainedly ill.

Because outcomes evolve over time, a single result is rarely the final word. A positive in-clinic test is typically confirmed with a second test — and because a recently exposed cat may convert from positive to negative as a regressive infection takes hold, veterinarians often retest after a number of weeks rather than acting immediately. More advanced laboratory testing, including PCR assays that measure the amount of virus integrated into the cat's DNA, can distinguish progressive from regressive infection and refine the prognosis.

What the Prognosis Really Is

This is where the reputation and the reality diverge most. A progressive FeLV infection does shorten lifespan: Cornell reports that survival after a diagnosis of progressive infection averages somewhere in the range of a couple of years, with many cats living roughly 2 to 3 years and a median around 2.5 years. Kittens fare worst, and progressively infected cats face the highest risk of fatal complications.

But averages hide an important truth. Cats with regressive infections often do far better than that figure suggests, and many reach old age without serious FeLV-related illness. With attentive care, a positive cat can have a good quality of life for a long time. The goals of care for an FeLV-positive cat are straightforward: keep them indoors to prevent both spreading the virus and picking up secondary infections, feed a complete and balanced diet, stay current on parasite control, and see the veterinarian at least twice a year — sooner at the first sign of illness — so that the secondary infections that actually threaten these cats are caught and treated early.

Prevention

FeLV is one of the more preventable serious feline diseases, and prevention rests on a few well-established measures:

A feline leukemia diagnosis is serious, but it is not the immediate sentence many owners fear. Understanding whether an infection is progressive or regressive, keeping a positive cat indoors and well-monitored, and protecting the cats around them through testing and vaccination can mean years of good life. The most powerful tools — a simple blood test and a vaccine — are also the most accessible, which makes FeLV one of those rare diseases where informed owners genuinely change the outcome.