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MedicalDictionary.comThe Free Veterinary Medical Dictionary
Medical Condition🐈 Catshematologic immune

Feline Leukemia Virus (FeLV)

🗣️ Pronounced:FEE-lyne loo-KEE-mee-uh VY-rus
In One Sentence (Plain English)

A contagious feline retrovirus transmitted primarily through close, friendly contact that impairs the immune system and predisposes cats to tumors and bone marrow failure.

Editorial Status: Verified from peer-reviewed veterinary sources (v1.0)
Updated: 2026-01-15

💬 In Plain English

Feline Leukemia Virus (FeLV) is often called the "friendly cat virus" because it is spread through close, affectionate contact—mutual grooming, sharing food and water bowls, and mother-to-kitten transmission through milk (unlike FIV, which spreads through violent bite wounds). Once inside the body, the virus invades bone marrow cells and the immune system. FeLV can cause severe anemia, suppress white blood cells leaving cats vulnerable to everyday infections, and dramatically increase the risk of cancers like lymphoma and leukemia.

🔬 Clinical & Technical Depth

For Vets & Technicians

Formal Clinical Definition

Gammaretrovirus infection exhibiting four clinical outcomes: abortive infection (cleared by immunocompetent host), regressive infection (provirus integrates but viremia controlled), progressive infection (persistent uninhibited viremia), and focal infection.

Why Veterinarians Use It

Veterinarians test every newly adopted cat, sick cat, or outdoor cat for FeLV using an in-clinic blood SNAP test.

Clinical Context Encountered

Encountered routinely in feline rescue shelters, stray cat evaluations, or when young cats present with severe non-regenerative anemia or lymphoma.

Clinical Reference Guide (Medical Condition)

Severity
Emergency StatusNon-Emergency Care
🚨 Red Flag Warnings (When to Contact an Emergency Vet)
  • •FeLV suppresses the immune system: minor respiratory or urinary symptoms in an FeLV-positive cat can rapidly escalate into life-threatening systemic sepsis.

❓ Questions to Ask Your Veterinarian

Take these actionable questions with you to your next clinic visit or appointment:

  • 1Did the in-clinic ELISA SNAP test detect FeLV p27 antigen?
  • 2Should a confirmatory IFA or quantitative real-time PCR test be sent to a reference lab to distinguish progressive from regressive infection?
  • 3How should I house an FeLV-positive cat to protect other cats in the home?
  • 4Is my FeLV-negative outdoor cat vaccinated with the FeLV core vaccine?

Academic & Clinical References