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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.