Feline Leukemia Virus (FeLV): What It Is, How It Spreads, and What a Diagnosis Means

A positive FeLV test used to be treated as close to a death sentence, and for a long time that shaped how people talked about the virus. The reality is more layered than that. Some cats clear the infection on their own, some carry it without ever getting sick, and some go on to develop serious illness, and knowing which outcome you're dealing with actually changes what a diagnosis means.

What feline leukemia virus actually does

Feline leukemia virus (FeLV) is a retrovirus that suppresses the immune system and, in some cats, causes cancers of the blood and lymphatic system, which is where the name comes from. According to the Cornell Feline Health Center, it remains one of the more consequential infectious diseases in cats worldwide, and it's specific to cats: it isn't contagious to people, dogs, or other pets in the house.

How it spreads

FeLV is shed primarily in saliva, and spreads through prolonged close contact: mutual grooming, shared food and water bowls, and bite wounds. The Merck Veterinary Manual notes that kittens are considerably more susceptible than adult cats, and a mother cat can also pass the virus to her kittens before birth or through nursing.

Why a positive test isn't one single outcome

This is the part that's changed the most in how vets talk about FeLV. The 2020 AAFP Feline Retrovirus Testing and Management Guidelines classify infection into three outcomes rather than a single "positive" category: abortive infection, where the cat's immune system clears the virus early and it never becomes detectable in blood; regressive infection, where the virus becomes dormant in bone marrow and the cat usually stays healthy, though the virus can potentially reactivate under stress or illness; and progressive infection, where the virus keeps replicating and the cat is expected to eventually develop FeLV-related disease. EveryCat Health Foundation notes that which outcome a given cat ends up with depends heavily on age at exposure, viral load, and how strong an immune response the cat mounts.

How testing actually works

The standard first test is an ELISA blood test, quick enough to run in a normal vet visit, which detects viral antigen in the blood. Because a single positive result can't yet distinguish a cat that's clearing the virus from one that's progressively infected, PetMD recommends retesting 8 to 12 weeks later, especially in young cats, to see whether the result resolves to negative or stays positive.

What a progressive diagnosis actually means for life expectancy

Large-scale studies have found an average survival time of roughly 2.4 years after a progressive FeLV diagnosis, with disease progressing considerably faster in kittens than in adult cats. That said, "average" hides a lot of range: some cats live for years with a good quality of life and manageable care, particularly indoor-only cats kept away from other infectious risks and monitored closely by a vet.

Frequently asked questions

Should FeLV-positive and FeLV-negative cats be kept separate?
Yes, cats with progressive infection should be housed separately from uninfected cats to prevent transmission, though this is a household management question best worked through with a vet based on the specific cats involved.

Is there a vaccine for FeLV?
Yes, and it's recommended for kittens and at-risk adult cats, particularly those with outdoor access or living with an infected cat, though it isn't universally considered a core vaccine for strictly indoor adult cats with no exposure risk.

Can a cat test positive and later test negative?
Yes, this is exactly what an abortive or transient infection looks like, which is why a single positive result in a young cat is often followed by a retest rather than treated as a final answer.

Sources

• Cornell Feline Health Center, "Feline Leukemia Virus"
• Merck Veterinary Manual, "Feline Leukemia Virus Disease"
• Little, S. et al., "2020 AAFP Feline Retrovirus Testing and Management Guidelines," Journal of Feline Medicine and Surgery, 22(1) (2020): 5-30
• EveryCat Health Foundation, "Feline Retrovirus Testing and Management Guidelines: Part One, FeLV"
• PetMD, "Feline Leukemia Virus (FeLV)"

This article is for general information and isn't a substitute for advice from your own veterinarian, who can test for and interpret FeLV status in your specific cat.