Cats with feline leukemia virus (FeLV) often show no symptoms at all in the early stages of infection. This is one of the trickiest things about the disease. A cat can carry the virus for weeks, months, or even years before visible signs appear, and some infected cats never develop symptoms at all. When signs do show up, they tend to be vague at first: weight loss, low energy, a dull or unkempt coat, and recurring minor illnesses that don’t fully resolve.
The specific symptoms your cat develops depend on how the infection progresses and which body systems the virus targets. FeLV can suppress the immune system, cause cancer, and damage bone marrow, so its effects are wide-ranging.
Not Every Infected Cat Gets Sick
This is important context before diving into symptoms. When a cat is exposed to FeLV, one of three things happens. About 20 to 30% of cats fight off the virus entirely and never test positive or show any signs. Another 30 to 40% develop what’s called a regressive infection, where the virus embeds in their DNA but the immune system keeps it in check. These cats are very unlikely to get sick, though the virus can reactivate later if they become stressed or immunocompromised.
The remaining 30 to 40% develop a progressive infection. This is the form that causes serious illness. The virus takes hold in the bone marrow and replicates continuously, putting the cat at high risk for potentially fatal complications. Kittens are far more likely than adult cats to develop progressive disease after exposure.
General Signs You Might Notice First
The earliest symptoms of FeLV tend to be subtle and easy to dismiss. Your cat may seem a little less playful than usual, sleep more, or lose interest in food. Gradual weight loss is common, sometimes noticeable only over weeks or months. The coat may look rough, greasy, or matted in a cat that previously groomed well.
Persistent or recurring fever is another early signal. Because FeLV weakens the immune system, your cat may cycle through minor infections that seem to clear up and then come back. Frequent upper respiratory infections, lingering sneezing, or runny eyes that don’t fully resolve with treatment can all point to an underlying immune problem.
Signs of Immune Suppression
The most common way FeLV causes harm is by crippling the immune system. A healthy cat fights off everyday bacteria, fungi, and viruses without you ever noticing. An FeLV-positive cat with a progressive infection loses that ability over time, leaving it vulnerable to infections that a healthy cat would shrug off.
What this looks like in practice:
- Skin infections and abscesses: Wounds, especially from bites, that heal slowly or keep getting infected.
- Chronic respiratory infections: Persistent sneezing, nasal congestion, or discharge that keeps returning.
- Mouth and gum inflammation: Red, swollen, or bleeding gums (gingivitis) and painful sores inside the mouth (stomatitis) that make eating difficult.
- Eye problems: A variety of eye conditions can develop, including inflammation inside the eye, cloudiness, or changes in pupil size.
If your cat seems to catch every illness going around, or if infections that should resolve with treatment keep coming back, that pattern itself is a symptom worth investigating.
Anemia and Bone Marrow Problems
FeLV has a particular affinity for bone marrow, the tissue responsible for producing red blood cells, white blood cells, and platelets. When the virus damages bone marrow, the most common result is anemia, a shortage of red blood cells that reduces the body’s ability to carry oxygen.
FeLV-related anemia is typically nonregenerative, meaning the bone marrow can’t produce new red blood cells fast enough to compensate. Only about 10% of FeLV-induced anemia cases involve the immune system actively destroying red blood cells. The visible signs of anemia in a cat include pale gums and inner eyelids, weakness, rapid breathing, and extreme lethargy. A cat with severe anemia may seem too exhausted to do much more than lie in one spot.
Beyond anemia, the virus can lower platelet counts, which increases the risk of unusual bleeding or bruising. It can also reduce white blood cell production, which further compounds the immune suppression already caused by the virus itself.
Lymphoma and Other Cancers
FeLV is one of the leading causes of cancer in cats, particularly lymphoma, a cancer of the white blood cells. Historically, lymphoma in the chest cavity and lymphoma spread throughout the lymphatic system were the most common forms, and both are closely linked to FeLV infection.
The symptoms of lymphoma depend on where the cancer develops. Lymphoma in the digestive tract causes weight loss, vomiting, diarrhea, and appetite changes. Lymphoma in the chest can cause difficulty breathing as fluid or tumor mass compresses the lungs. Other possible signs include masses on or under the skin, nasal discharge, and in rare cases, seizures if the cancer reaches the nervous system. In many cases, the first noticeable signs are nonspecific: weight loss, poor appetite, and lethargy that gradually worsens.
Neurological and Reproductive Signs
Less commonly, FeLV can affect the nervous system, leading to neuropathies. These may show up as changes in behavior, unsteadiness when walking, weakness in the hind legs, or seizures. These symptoms can be alarming and tend to appear in later stages of disease.
In unspayed female cats, FeLV can cause reproductive failure. This includes miscarriage, stillborn kittens, and “fading kitten syndrome,” where newborns seem healthy at birth but rapidly decline and die within the first few weeks of life. If a breeding cat repeatedly loses litters, FeLV is one of the infections that should be ruled out.
How Quickly Symptoms Develop
There’s no single timeline for FeLV. Some cats develop symptoms within months of infection, while others remain healthy for years. The key factor is whether the infection becomes progressive. In a progressive infection, the virus replicates continuously, and the risk of serious disease climbs over time.
One large study tracking FeLV-positive cats found a median survival time of about 714 days (roughly two years) from the time of diagnosis, compared to nearly 11 years for cats that tested negative. Cats with low red blood cell counts at the time of diagnosis had significantly shorter survival times. These are averages, though. Individual cats vary widely, and some FeLV-positive cats with regressive infections live normal lifespans.
How FeLV Is Diagnosed
Because symptoms are so varied and often overlap with other conditions, diagnosis relies on blood testing rather than symptoms alone. The standard approach is a two-tier system. A point-of-care screening test checks for viral proteins in the blood. A negative result in a low-risk cat is generally reliable. A positive result may need confirmation with a second test using a different method, since false positives are possible.
Timing matters. A single test can’t always tell you whether an infection is progressive or regressive. A cat that tests positive should be retested 6 to 12 weeks later. If the test is still positive, the infection is likely progressive. If it has turned negative, the cat’s immune system may have controlled the virus.
Cats should be tested after adoption, after any known exposure to an infected cat, before vaccination, and whenever unexplained illness develops. If your cat is showing any of the symptoms described above, especially in combination, testing for FeLV is a straightforward first step that can guide everything that follows.