Feline Leukemia Virus: Risks, Diagnosis, and Prevention for Your Cat

Feline leukemia virus (FeLV) is the most common infectious disease in domestic cats in the United States, affecting approximately 2–3% of the population.

How Does a Cat Contract FeLV?

The virus is shed in saliva, nasal secretions, urine, feces, and milk. Transmission occurs through bite wounds, hissing, mutual grooming, and casual contact such as shared litter boxes and feeding dishes. Mother cats can also pass the virus to kittens before birth or while nursing. To minimize risk, keep new or untested cats separate from established household cats until a negative FeLV test is confirmed.

High‑risk cats include those that live with an infected cat, those allowed unsupervised outdoor access where bites are possible, and kittens born to infected mothers.

How Does FeLV Affect a Cat?

While many FeLV‑positive cats enjoy long, healthy lives, the virus is the leading cause of cancer in cats. It can trigger blood disorders and immune suppression, making otherwise harmless bacteria, viruses, protozoa, and fungi potentially lethal.

Diagnosing FeLV

Veterinarians use blood tests to diagnose FeLV. The standard screening tool is an ELISA test, typically performed in a clinic. Because the virus can take 8–12 weeks to become detectable after exposure, a follow‑up test at three months is recommended for high‑risk cats.

Always consult your veterinarian to determine the best testing schedule for your cat.

Treatment Options

There is no cure for FeLV. Care focuses on managing secondary infections: antibiotics for bacterial disease, blood transfusions for severe anemia, and prompt treatment of any other medical issues. FeLV‑positive cats should be kept strictly indoors in single‑cat households to prevent spread. Raw food diets are contraindicated for immunocompromised cats due to infection risk.

Preventing FeLV in Your Cat

The Feline Vaccination Advisory Panel recommends vaccinating all kittens. The vaccine series requires two shots spaced 2–4 weeks apart. For adult cats, vaccination is considered non‑core unless they are at risk of exposure. Loyal Companions Animal Hospital offers a FeLV vaccine that only needs a booster every two years for at‑risk cats.

Before introducing a new cat to your home, test for FeLV or keep it isolated until results are known. The safest protection is to keep cats indoors and away from potential FeLV‑infected animals. If outdoor access is allowed, supervise or use a secure enclosure to prevent wandering and fights. Never share food, water, or litter boxes between infected and non‑infected cats. If an infection is discovered, test all household cats and, if possible, separate infected from healthy cats.

When considering vaccination for uninfected cats, discuss exposure risk and the benefits versus drawbacks with your veterinarian. Even vaccinated cats benefit from ongoing preventive measures.

Prognosis

Many FeLV‑positive cats live normal, extended lives with proper care. Regular monitoring of weight, appetite, activity, elimination, oral and ocular health, and behavior is essential. Any changes should prompt immediate veterinary consultation.