Feline Leukemia

Feline leukemia virus (FeLV) is a retrovirus that infects cats and suppresses the immune system, making them vulnerable to secondary infections, anemia, and certain cancers. It spreads through close contact — saliva, nasal secretions, urine, and milk — and is one of the most common infectious causes of death in cats.

What Is Feline Leukemia?

Feline leukemia virus (FeLV) is a retrovirus — it inserts copies of its genetic material into the infected cat’s cells. Once established, the virus attacks the immune system similarly to how HIV affects humans (though FeLV cannot infect people). It is estimated to affect 2–3% of all cats in the United States, with higher rates among outdoor and multi-cat households.

Not all cats exposed to FeLV become permanently infected. About 30% of exposed cats develop a persistent (progressive) infection, while others may fight off the virus or develop a regressive infection where the virus remains dormant.

FeLV is classified into subgroups (A, B, C, and T), each associated with different disease outcomes including lymphoma, leukemia, anemia, and immunosuppression.

How FeLV Spreads

FeLV spreads through prolonged close contact between cats. The most common transmission routes include:

• Mutual grooming and sharing food bowls — saliva is the primary transmission vector
• Bite wounds — especially during fights between outdoor cats
• Mother to kitten — in utero or through nursing milk
• Shared litter boxes — though less common than saliva transmission

The virus does not survive long outside a cat’s body and is easily killed by disinfectants, sunlight, and drying. It cannot spread to humans or dogs.

Signs and Symptoms

FeLV-positive cats may appear healthy for months or even years before showing symptoms. When the disease progresses, signs may include:

• Weight loss and decreased appetite
• Pale gums — a sign of anemia
• Recurring infections — bladder, skin, or upper respiratory infections that keep coming back
• Swollen lymph nodes
• Fever — persistent or recurrent
• Poor coat condition — dull, matted, or thinning fur
• Diarrhea — chronic or intermittent

Because these symptoms overlap with many other conditions, the only way to confirm FeLV is through a blood test at your veterinary clinic.

What Pet Owners Should Do

• Test all new cats. Before introducing a new cat to your household, have them tested for FeLV. Kittens should be tested at least twice.
• Vaccinate. The FeLV vaccine is recommended for all kittens and at-risk adult cats (outdoor cats, cats in multi-cat homes). Discuss the schedule with your vet.
• Keep FeLV-positive cats indoors. This protects other cats in the neighborhood and shields your cat from secondary infections.
• Separate FeLV-positive cats. If you have both positive and negative cats, keep them in separate living areas with separate bowls and litter boxes.
• Schedule regular vet visits. FeLV-positive cats should see the vet at least twice a year for monitoring.

Frequently Asked Questions