Feline leukemia virus
Also known as: FeLV, Feline Leukemia Virus Infection
In short
Feline Leukemia Virus (FeLV) is a common retrovirus in cats that compromises the immune system and bone marrow, often leading to severe anemia, cancers like lymphoma, and life-threatening secondary infections.
TL;DR. Feline Leukemia Virus (FeLV) is a common retrovirus in cats that compromises the immune system and bone marrow, often leading to severe anemia, cancers like lymphoma, and life-threatening secondary infections.
FeLV replicates within the lymphoid tissues and bone marrow of infected cats.
Feline Leukemia Virus (FeLV) is a widespread and serious viral infection that affects cats worldwide. As a retrovirus, FeLV has a unique way of reproducing inside a cat's body. Once a cat is exposed, the virus targets and replicates within the lymphoid tissues and bone marrow. This replication disrupts the normal production of blood cells and weakens the cat's immune system, leaving them highly vulnerable to secondary infections, anemia, and certain types of cancers.
To understand how FeLV takes hold, it helps to look at how the virus operates at a cellular level. A leading veterinary internal medicine reference explains:
"The virus produces reverse transcriptase, which catalyzes the reaction, resulting in the formation of a DNA copy (provirus) of FeLV viral RNA in the cytoplasm of infected cells; the provirus is inserted into the host cell genome. On subsequent host cell divisions the provirus serves as a template for new virus particles formed in the cytoplasm and is released across the cell membrane by budding."
By embedding its own genetic material directly into the cat's DNA, the virus becomes a permanent part of the host's cells. This allows it to persist and replicate silently before clinical signs appear. The consequences of this cellular hijacking are diverse and severe. FeLV can cause profound immunodeficiency, destroy red blood cells, and trigger the uncontrolled cell division that leads to leukemia or lymphoma.
FeLV is primarily spread through close, friendly contact between cats. The virus is shed in high quantities in saliva, as well as in nasal secretions, urine, feces, and milk. Common routes of transmission include mutual grooming, sharing food and water bowls, and bite wounds sustained during fights. Mother cats can also pass the virus to their kittens during pregnancy or through nursing.
Outdoor cats, intact male cats, and cats living in multi-cat households where the infection status is unknown are at the highest risk of contracting the virus. Kittens are highly susceptible to infection, whereas older cats develop a degree of natural resistance as their immune systems mature. There are no known breed predispositions to FeLV; any cat, regardless of breed, can contract the virus if exposed.
Because FeLV affects multiple body systems—particularly the blood-producing organs and the immune system—the symptoms can be incredibly varied. Some cats may remain asymptomatic for months or even years, while others show rapid decline.
Lethargy and pale gums are common signs of severe anemia caused by FeLV.
Diagnosing FeLV requires a combination of clinical evaluation and specific laboratory tests. Because the virus moves through different stages in the body, your vet may need to perform multiple types of tests to understand the exact status of the infection.
To identify the virus, vets rely on several key diagnostic tools:
Your vet will interpret these results carefully, as some cats can clear the initial stage of infection (transient viremia) and test negative later. It is also important to note that other testing methods have limitations. As noted in veterinary literature:
"Antibody titers to FeLV envelope antigens (neutralizing antibody) and against virus-transformed tumor cells have been detected in research studies, but the diagnostic and prognostic significance of results from these tests is unknown. Real-time PCR assays are more sensitive than conventional PCR for FeLV infections, but validated and standardized assays are not currently available in the United States."
ELISA testing is the primary screening tool used to detect the FeLV p27 core protein in a cat's blood.
There is currently no definitive cure for Feline Leukemia Virus. Once the virus has permanently integrated into the cat's bone marrow cells, it cannot be completely eradicated. However, veterinary medicine offers several supportive and targeted therapies to manage the symptoms, suppress viral replication, and improve the cat's quality of life.
Your vet may consider specific antiviral medications to help slow down the replication of the virus.
These therapies aim to regulate or boost the cat's natural immune response to help them fight off the virus and secondary opportunistic infections.
Because FeLV causes a wide range of secondary complications, targeted supportive care is vital:
The prognosis for cats with progressive, persistent FeLV infection is guarded. The majority of persistently viremic cats die within 2 to 3 years of diagnosis due to complications such as severe immunodeficiency, opportunistic infections, nonregenerative anemia, or aggressive cancers like lymphoma.
However, the outcome can vary depending on the cat's individual immune response. Some cats experience a "regressive" infection, where their immune system successfully contains the virus, keeping it dormant. These cats can live normal, healthy lives for many years, though they may still be at risk of reactivation if they become severely stressed or immunocompromised later in life.
Preventing exposure is the most effective way to protect cats from FeLV.
If your cat has been diagnosed with FeLV, close monitoring is essential. You should contact your veterinarian if you notice any changes in their behavior, appetite, or energy levels.
Seek immediate emergency veterinary care if your cat displays any of the following red-flag signs:
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
Feline Leukemia Virus (FeLV) is a common retrovirus in cats that compromises the immune system and bone marrow, often leading to severe anemia, cancers like lymphoma, and life-threatening secondary infections.
Anorexia、Azotemia、Depression、Nonregenerative anemia、Thrombocytopenia、Weight loss、bilirubinuria、hyperbilirubinemia
ELISA、IFA、PCR、p27 core protein detection
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
Peqaboo’s AI helps you track symptoms, understand lab reports, and know when to see a vet.
Get the Peqaboo app
