Feline Leukemia Virus (FeLV)

Feline Leukemia Virus.

Few words are scarier to a cat lover than those.

And, with good reason, even though a positive Feline Leukemia Virus test is not always a death sentence. Let’s look at both the disease and testing in detail.

Feline Leukemia Virus (FeLV) is a retrovirus, meaning that it uses an enzyme called reverse transcriptase to insert itself into the host’s genetic material.

FeLV is often called “the virus of friendly cats” because of the way it is transmitted. An uninfected cat becomes infected by “friendly” interaction with an infected cat. Sharing water bowls, food bowls, litterboxes and licking and grooming one another are common means of transmission.

Don’t be fooled, however. Unfriendly interaction, such as fighting, can also transmit the disease.

If your cat or kitten goes outdoors and interacts with an FeLV-infected cat in one of these ways and is not protected by means of vaccination he is very susceptible to becoming an FeLV-positive cat himself.

The first thing to happen is that the virus replicates (reproduces) itself and spreads throughout the body via the bloodstream in a process called primary viremia. After the initial viremia one of three scenarios will occur.

  1. Most commonly the body’s white blood cells will become permanently infected by the virus and the cat will be chronically infected. This group constitutes about two-thirds of infected cats. About half of this group will continue to test positive on a blood test for FeLV.
  2. About one-third of cats will become infected, then the immune system will rid the body of the virus permanently, almost like he had never been infected. These cats, if they are truly virus-free, will test negative on a blood test for FeLV and will live a normal life.
  3. About half of cats in the first group, or a third of all infected cats will sequester their virus in the bone marrow. These cats will continue to test negative on a blood test, but can be proven to actually be infected by performing an immunofluorescent assay (IFA) on a bone marrow sample. Periodic viremia may occur and during those times a blood test will also be positive. However, it is impossible to know when viremia is occurring.

Or so we thought for many, many years. A new research tool, polymerase chain reaction (PCR), makes it apparent that there are four outcomes following FeLV exposure, two common scenarios and two uncommon.

  1. Progressive Infection in which the victim becomes infected with the virus, experiences a primary and secondary viremia and eventually succumbs to an FeLV-associated syndrome within months or years of infection.
  2. Regressive Infection in which the victim becomes infected, experiences primary viremia, but then no longer has whole, infective virus in the bloodstream. These cats circulate proviral DNA in their blood, but have little risk of developing FeLV-associated diseases.
  3. Abortive Exposure while quite rare, seems to prevent virus from ever replicating in the cat’s body. After exposure, these cats test negative for FeLV with every known method.
  4. Focal Infections, also rare, isolate the virus in certain body parts or organs. Spleen, mammary glands, intestines and lymph nodes have been confirmed to be sites of focal infection., while quite rare, seems to prevent virus from ever replicating in the cat’s body. After exposure, these cats test negative for FeLV with every known method. in which the victim becomes infected, experiences primary viremia, but then no longer has whole, infective virus in the bloodstream. These cats circulate proviral DNA in their blood, but have little risk of developing FeLV-associated diseases. in which the victim becomes infected with the virus, experiences a primary and secondary viremia and eventually succumbs to an FeLV-associated syndrome within months or years of infection.

As fascinating as all of this information is, its application is somewhat academic. Our concern is whether a cat is well. Or not.

If he is well, we need to have two consecutive negative tests about two months apart and a repeat test any time he might be exposed to a known or suspected infected cat or has clinical signs associated with syndromes typical of FeLV-infected cats.

If he is not well we will pursue testing to whatever level required to prove that he is ill from Feline Leukemia Virus, or something else.

Click here to understand testing for both Feline Immunodeficiency Virus and Feline Leukemia Virus.

 What does an ill FeLV-infected cat look like?

Generally, he looks like a sick cat. Imagine anything that the immune system should be protecting your kitty from, but isn’t.

For example, nearly 100% of cats with chronic, recurrent or non-responsive sinusitis will test FeLV positive, either on a blood or bone marrow test.

Other chronic syndromes are also seen: urinary tract infections that won’t get well or keep coming back, skin problems that don’t respond to treatment, the list goes on and on.

Many cats succumb to lymphoma, leukemia and other cancers.

How are FeLV-infected cats managed?

First and foremost the infected cat must be isolated. He must be made to be a totally indoor cat. If he goes outside he will infect other cats he comes into contact with. If he interacts with sick cats he will almost assuredly come down with whatever disease they have, further weakening his immune system.

If there are other cats indoors, the FeLV-infected cat must live alone, or with other FeLV-positive cats. Remember, this is a virus of friendly cats. Healthy cats must not share litterboxes, water or food bowls or living space with FeLV-ill cats.

His symptomology can be treated. If he has respiratory or urinary infections he may be treated with antibiotics. Convenia is a good choice for those patients in which it is effective because it relieves the owner and the patient from daily or twice-daily medication administration.

Treatment for cancer can range from palliative to aggressive, depending on the patient’s overall condition and the owner’s willingness to treat.

Immune system stimulants such as Enisyl  can help.

How long will my FeLV-infected cat live?

Longevity is impossible to predict. The single biggest determinant is length of time since infection, and we rarely know when any given cat was actually infected.

An individual with a strong immune system will last longer than a cat with a genetically weak immune system. An indoor cat will usually outlive an outdoor cat. A cat infected with both FeLV and Feline Immunodeficiency Virus (FIV) will not be with us very long. Cats with cancer have a particularly poor prognosis. Cats who receive aggressive therapy for their secondary signs will usually live longer than those without treatment.

Don’t give up hope just because of a positive test series and/or confirmation IFA. Well-protected cats living in healthy conditions can live for many years with FeLV.

My own “personal best” story is a patient who lived over five years from the time we diagnosed his positive status.

MyPetsDoctor.com expresses our gratitude to Dr. Julie Levy and her associates who published much of this information in The Journal of Feline Medicine and Surgery, 2008.MMFeLV

See you tomorrow, Dr. Randolph.

4 comments

  1. Laura Kanipe says:

    Thank you Dr. Randolph for replying to my concerns about my cat Hailey. You have raised some questions for me that I had not known to ask or be concerned about, and that I plan to consult with my Veterinarian about. The Radiograph of Hailey was one simple side or length view of her entire system and the only thing my Veterinarian mentioned was that he saw no blockage or anything wrong with her organs. He did not tell me her exact RBC count, hematocrit, or hemoglobin only that the results meant a Leukemia diagnosis. I plan to get that information from him soon and his thoughts about anemia? This information would undoubtedly tell me how far along the Leukemia has progressed, I’m assuming?
    In answer to your question about Hailey’s IBD, she was diagnosed with it in 2009, was on prednisolone daily for a year until I did some research on the effects of the prednisolone on the liver, and realized that through a change in her diet (a change in food protein) and the addition of probiotics and enyzymes…that I could “possibly” get her digestive tract back to normal. Most of my information come from reading research by a Veterinarian who also integrates a holistic view in her practice…Dr. Karen Becker who essentially advised IBD as a developed allergy from eating the same protein…so I changed or alternated the protein in Hailey’s diet, gave her a canned grain free diet, with the addition of probiotic and enzyme supplements…and it was a slow process of finding a healthy diet she liked and slowly reducing the prednisolone, but after 9 months Hailey was no longer on the prednisolone, and in my opinion the process worked remarkably. Hailey had no further IBD concerns after early 2011. From 2009 to 2011 (when she had the IBD)she had at least two blood panels done mostly at the Veterinary Hospital, and clinic Doctor’s never indicated an abnormality in her RBC’s or WBC’s or the possiblity of Leukemia. She has always been an indoor cat and the possiblity of her having Leukemia has never been a thought for me…and probably not for the Veterinarians….though now I realize after reading that the virus can lay dormant in the bone marrow?
    By the way I found your research on H1N1 very interesting and believe myself that I recently had the H1N1 virus…I work in a health related field where germs get passed quickly….but can never be sure if I recently passed it to Hailey.
    Since I last updated you on Hailey, her symptoms and over-all status has improved. After day four on the Covenia she showed absolutely no signs of improvement and seemed to be getting worse. I consulted with my Veterinarian, and he encouraged me to give the Covenia a chance, before adding or considering other drugs….as I wanted to know if there was something he could give her for her labored breathing. On day 5 of the Covenia I decided to give Hailey some Immune Harmony for Pets, pet enzymes, and probiotics, with a Syringe, and after about two hours of the first dose of Immune Harmony (products from the AskAriel.com website-another Vet. that incorporates a holistic approach), Hailey came out from hiding, showed some interest in eating and drinking and walked about the house a little. She is now 7 days on the Covenia, and three days on the immune supports and each day I have seen gradual improvement. Each day she eats more,is urinating and having normal bowel movements, her breathing has improved (slowed) drastically, though not completely normal, and she sleeps restfully. She had been restless, unable to sleep, and reluctant to move, and is now moving about the house, and jumping up on furniture, though she tires easily. I can only hope she will continue in the next week to show more progress, but I do not know what to expect after that…except to take one day at time.
    Thank you for the questions and advice as they help me understand her condition and can help me form and direct my decision making in regards to her care. As you can probably tell, she is a very loved cat! Thank you for sharing your knowledge with me.

    • Thank you for the update, Laura. Our readers and I are pulling for you and Hailey! We are delighted to hear that she is feeling better, and our prayers will be for continued recovery. FeLV is a bad condition, but some patients can do well for years while infected with it. I emphasize some. Please continue to send in reports.

  2. Laura Kanipe says:

    My Maine Coon cat Hailey is a almost 12 yr. old feline. As a young cat she developed at least one cat cold every year, rather mild in nature, with good success at the Vet.s office getting rid of them but has seemed sicklier than most of my other cats in my family. Around age 8 or 9 she got really sick, projectile vomiting, lethargic, not eating, and after about a two week stay at an emergency clinic she gradually got well, and was diagnosed with IBD. During about a 16 month span, I changed her diet, gave her probiotics and pet enzymes and got her off the prednisolone the Emergency clinic had diagnosed she would always be on. She was symptom free for about two or three years, until last year I took her in to the same emergency clinic for IBD related symptoms and she recovered quickly. Last week I came home with the flu, and shortly after Hailey exhibited a runny nose, slight tiredness, not eating much, and then she projectile vomited a hairball, and for at least a half day after the hairball her breathing was heavy and rapid. Since she recovered after half a day I figured the hairball just taxed her a good deal, but when two days later she started the rapid breathing again, and had still exhibited signs of an URI, (nasal drip, sneezing) I took her to my Veterinarian (epecially considering her IBD hx.), in which he did a blood test and took an xray, and ruled she now has Feline Leukemia. I was given no other diagnosis for her current symptoms or problem…whether currently she had a URI to fight off or what. I am guessing the Vet ruled she had a infection or virus of some type. What was made clear was that she needed an antibiotic for her “complications”, and I was told the Leukemia would would make her more susceptible to viruses in the future and make it harder for her body to figh t off infections. This I understand. He gave her the Covenia (1 shot=2wk. dose). One of my other cats received Covenia and it helped him with his UTI. Hailey also got an appetite stimulant, pill form, to take every three days (10 doses or a months worth) and a vitamin B12 injection. Her xrays revealed nothing abnormal…(and to note I have recently read that H1N1 flu can be transmitted to cats). I took Hailey home and we are now on day three of the Covenia, and I have noticed some slight improvement, as she has shown signs of wanting to roam around the house, signs of eating, and is getting some rest. Her sleep seems short (30 min. naps) followed by two hours of wake time where she roams the house and quickly tires herself and sits awake for a bit longer before trying to sleep. I am still having to give her a teaspoon of water in a syringe every few hours as she has no desire to drink on her own. She is also getting water in some of the food she eats, but she only ta kes a small tid-bit of a bite or two before she is done with it. I am probably getting an ounce of food in her a day for the past two days. Luckily it is a holiday weekend and I can spend my days tending to her. The appetite stimulant seems to help after a dose is given, but in my opinion it seems to fade after a day… and she is to get the appetite stimulant every 3 days. What has me concerned is that her labored breathing continues. It was never really addressed by the Vet. and I guess I am wondering if he thinks the heavy breathing will subside completely as the Covenia clears up the infection or virus (?) out of her system? I have noticed a slight improvement in her breathing, mostly when she is at sleep, but it is still is not normal breathing. I have noticed no nasal drip or sneezing. I think after one week on Covenia, if her breathing has not improved as well as her appetite and other symptoms I will consult with my Vet. I have not consulted with my Vet. si nce he gave her the medications since it happens to be a holiday weekend. After mulling over her Leukemia diagnosis and doing a little research, I have decided my goal is to work with my Vet. to get Hailey better and rid her of the current infection, and then once she is better continue with her good diet and start her on some enzymes, probiotics, and immune system support to help keep her as strong as possible, and prevent future infections or viruses. I guess my question for you (as long and drawn out as I have been here), and not having the information to provide you more of a diagnosis and only symptoms, do you think the Vet. made a good choice with Covenia…and how is he thinking the Covenia is going to help her with her rapid breathing? I guess I am as all of us do, want to see more of an immediate result. Do you think her rapid breathing may be a symptom of a URI since the xray revealed no noticeable physical complications, and as the infection or virus clears (assuming that is the diagnosis) that her breathing should return to normal? Would you as a Vet. have went in the same course of medication therapy as my Vet., and do you think there is any other medications the Vet should have her on, or try her with, especially if the Covenia has not completely recovered Hailey at the end of two weeks? I will be asking my own Vet. the same questions as time goes on, but I guess I need a second perspective. After reading a little about Hailey’s Leukemia diagnosis, I seem to feel she still has a good survival rate yet, and plan to take a preventive and quality of life approach, one day at a time, rather than a more negative approach, since she has exhibited no other problems. Thanks for any help and advice you can give.

    • Your kitty’s situation is complicated. Please read the above post on Feline Leukemia Virus for a better understanding of the disease. You can also use the SEARCH window in the upper right hand corner to search for FeLV for even more posts on the topic. I have also written extensively on H1N1 in dogs and cats. Click here to read one post, or SEARCH for H1N1 for more. Some questions arise: 1, How long since her last negative FeLV test? 2, You say the doctor took an Xray. What part of the body was radiographed? If the chest was completely normal, including the mediastinum, you are miles ahead. If there is any question about the mediastinum, the radiograph should be sent to a board-certified radiologist for reading. 3, Hailey is off prednisone for her IBD. How is that being managed? Few IBD patients are completely medication-free. 4, On the CBC, what was her RBC count, hemogolobin and hematocrit? Are we sure she isn’t breathing hard because she is anemic? Convenia is an excellent long-acting antibiotic, but few cats’ upper respiratory conditions are purely bacterial, so supportive therapy is important while the body battles such viruses as Feline Rhinotracheitis Virus. Please keep us updated on Hailey’s condition and feel free to use the COMMENT box above if you have more questions. Best wishes, Dr. Randolph.

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