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The Feline Leukemia Virus: What You Need to Know

By Lea Jaratz

feline leukemia virus

Feline leukemia is one of those things that you may have heard of, but often don’t know much about until it’s hit close to home. After my mom lost one of her three cats to feline leukemia last month, I wanted to study up a bit to see if I could sort out what happened and how she might protect the remaining two. Take a moment to read on, and perhaps save the life of a cat close to your own heart.

What is feline leukemia virus (FeLV)?

Feline leukemia virus (unlike human leukemia) is a contagious disease that is transmissible between cats. While relatively rare (2-3% of the population is infected), it is the most common infectious disease amongst cats, and the fact that a cure has yet to be found makes it quite serious.

Not all cats that are exposed to FeLV will contract the disease. Kittens and sick cats are most likely to develop the disease. However, healthy cats may contract the disease after repeated or prolonged exposure, such as living with an infected cat or spending a lot of time outdoors.

Of the cats exposed to FeLV, roughly one third will not develop any infection. Another 30 percent will develop a short term or transient infection and only be sick (and contagious) for a few months. A small percent of cats (5-10 percent) will develop a latent infection, wherein their blood and saliva are no longer infected but their bone marrow still carries the infection. These cats are susceptible to repeat infection and shedding of the disease at a later time.

A remaining 30 percent will develop the fully-persistent infection and are likely to have a shorter life as a result.

The Spread

FeLV is transmissible between cats via saliva, blood, nasal secretions, milk, urine, and feces. It’s most likely transmitted via bite wounds and mutual grooming. While it’s rare for FeLV to be spread by sharing water bowls or litterboxes, this is common.

FeLV is not transmissible to humans, dogs, or other non-feline species.


There is a vaccine for FeLV, though it is not recommended for every cat. Firstly, it does not guarantee immunity, so some cats that receive it may still contract the virus. Secondly, if a cat is not likely to be exposed to FeLV, it may not be essential.

The only guaranteed method of prevention is to prevent exposure. Cats should not be allowed to roam freely outside, and you should always have a new cat tested for FeLV before introducing them to healthy cats. If you find out that one cat has FeLV, she should be quarantined while others are tested. (Testing is done at your veterinarian’s office, using a blood test called ELISA.)

What is the prognosis for a FeLV+ cat?

While some therapies and special diets may help a cat remain healthy for a bit longer, most FeLV+ cats will live only 2-3 years past the time of a positive diagnosis. It may depend on which type of FeLV infection the cat has. There are three types, and a FeLV+ cat may have one, two, or all types.

FeLV A (occurs in 100 percent of infected cases) weakens a cat’s immune system, making them likely to develop secondary infections.

FeLV B (occurs in roughly 50 percent of infected cases) can cause irregular tissue growth. While not the same as human leukemia, roughly 60 percent of FeLV B positive cats will develop cancer, while another 40 percent will experience other abnormal tissue growth.

FeLV C (occurs in only 1 percent of infection cases) can cause severe anemia.

What does having a FeLV+ cat mean for me?

If your cat is FeLV+, you can expect them to have a good quality of life, though their life may be shortened. Your cat will need to eat a high-quality diet and avoid exposure to sick cats as well as FeLV- cats. There are some therapies available, though you should discuss the pros and cons with your vet to determine if the efficacy will outweigh the potentially harmful side effects.

It’s tough to know what may lie ahead for a cat with FeLV. While it’s a difficult diagnosis, many shelters and rescues are looking for adopters willing to allow a FeLV+ cat to live life as an only cat in their homes. If you’re willing to give a lot of love to a cat for a shortened period of time, it can be very rewarding.

Hopefully, you will never experience this difficult diagnosis with one of your own cats, but remember that each case of FeLV is as different as can be. Working with your vet to understand your own cat’s risks and prognosis can make living with FeLV quite manageable.

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