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Feline Leukemia

Randy Walker DVM

What Is Feline Leukemia?

Feline Leukemia (abbreviated Felv), is an infectious disease of cats caused by the Feline Leukemia Virus.

What Are The Symptoms Of Feline Leukemia?

Feline Leukemia can take several basic forms and these are (1) anemia, weakness, & progressive weight loss; (2) cancerous tumors; (3) opportunistic diseases (respiratory tract infections, infectious peritonitis, abscesses, etc), resulting from the suppressed immune system & (4) the subclinical carrier state. Many cats with Feline Leukemia will experience progressive weight loss, anemia, leukopenia (meaning a decrease in the number of disease fighting white blood cells), weakness, and eventually death. Those cats who develop cancerous tumors will usually exhibit many of these same signs. Also, any cat who experiences recurring infections is highly suspect for infection with the Feline Leukemia virus. Feline Leukemia is usually fatal.

Can Feline Leukemia Virus Be Compared With The AIDS Virus (HIV) In People?

Although they are entirely different viruses and Felv is NOT transmissible to people, Feline Leukemia can be somewhat similar to the AIDS virus in the overall effects it has on the patient's body (weight loss, anemia, secondary infections, low white blood cell count, etc). This is a handy way for many owners to understand it.

How Can My Cat Catch Feline Leukemia?

Feline Leukemia virus is transmitted primarily through the saliva of infected cats. This usually occurs through bite wounds, cats grooming each other, or sharing food bowls or water bowls. Hissing through a screen window will sometimes transmit enough saliva to cause an infection. Other high risk situations include encountering strange cats in boarding or grooming facilities. The virus lives only a few minutes outside of the body so transmission is usually through direct contact between cats. It is not uncommon, however, for us to encounter a cat who is dying of Feline Leukemia infection for which we can find no history of exposure to suspect cats. This leads us to believe that transmission must be much easier than is often recognized.

If My Cat Is Exposed To An Unfamiliar Cat, Doesn't The Unfamiliar Cat Have To "Look Sick" To Be A Carrier Of Felv?

No. While many cats who have Felv have notable signs of illness (weight loss, unthriftiness, dull coat, etc) some do not. A cat can be infected with and contagious with Feline Leukemia and appear perfectly normal. In fact about 30-50% of the local cats that we diagnose with Feline Leukemia virus are detected through the routine blood test that we do in preparation for vaccination. Although a cat infected with Feline Leukemia virus will usually eventually die from the disease, it can sometimes be months or years before clinical signs become evident.

How Serious Is Feline Leukemia Nationwide?

Feline Leukemia is the leading infectious cause of death in cats nationwide. It is a tragic epidemic.

I've Heard That Sometimes A Cat Can Recover From Feline Leukemia. Is This True And How Does This Happen?

When a cat is exposed to the Feline Leukemia virus one of three things will happen: (1) the cat rids the virus from its system and infection does not persist; (2) the cat goes into the chronic carrier state in which it "reaches a stand-off" with the virus; or (3) the cat dies from the effects of the Feline Leukemia virus within weeks to months. The vast majority of the so-called "recoveries" are the cats in group #1 in which the cat's immune system rids the body of the virus before the infection reaches the bone marrow to cause a persistent infection. Although this can happen its actually a very small percentage of the unvaccinated cat population that we see this in. Cat's who become sick with full-blown Feline Leukemia almost never recover just as human beings with full blown AIDS won' t recover.

Briefly, Describe The Chronic Carrier State For Feline Leukemia.

This is the situation in which the cat becomes infected with Feline Leukemia but does not immediately die of the disease. In this situation, the leukemia virus has established itself in the cat's body (bone marrow, spleen, lymph nodes, etc) such that the cat is not able to rid it from its system but is able to keep it relatively under control. Cats in the chronic carrier state usually do die from Feline Leukemia at some future date but it sometimes takes years for this to occur. These individuals often have an up & down roller coaster existence between severe illness and relative good health. During this time the chronic carrier is infectious and a threat to other cats.

What Are The Chances That My Cat Can Contract Feline Leukemia From A Stray Cat That Walks Up Into Our Yard?

Due to the high prevalence of Felv, many (probably most) stray cats are exposed to Feline Leukemia (thorough bite wounds, mating, etc). Of those that are exposed, most of them will die relatively quickly. This leaves the chronic carriers as the survivors and therefore the odds are great that a stray cat who walks up into the yard is a carrier of Feline Leukemia.

Is There Any Cure For Feline Leukemia?

No. We have no medication which works directly against the virus itself. Our therapy for the Feline Leukemia patient is directed toward improving the general health of the body (with vitamins, nutritional supplements, etc) and fighting secondary infections (through antibiotics). What Is The Prognosis For Feline Leukemia? For most cases of Feline Leukemia the prognosis is extremely guarded to grave.

How is Felv Diagnosed?

The most common method for diagnosing Feline Leukemia is to look for the presence of the virus in a small sample of the cat's blood. We do this test routinely in the veterinary laboratory.

How Can Feline Leukemia Be Prevented?

We guard against Feline Leukemia through vaccination.

Does My Cat's Annual Distemper 3-Way Vaccination Protect Against Feline Leukemia?

No. These are completely different diseases.

Briefly, Outline A Complete Feline Leukemia Prevention Program

We recommend a routine blood test first to rule out pre-existing infection. If this is negative (meaning that no virus is found in the bloodstream) then we give an initial injection of the Feline Leukemia vaccine followed by a booster injection three weeks later. Then we give a booster injection once-a-year thereafter.

Why Should a Cat Be Tested Before Receiving The Vaccination?

Because a cat can have Feline Leukemia and not show external signs yet. It is not uncommon at all to find a positive on a routine test.

Do You Recommend Vaccinating A Cat Who Already Has Feline Leukemia?

No. The vaccination will not protect a cat who already has Feline Leukemia. Vaccinating a positive cat is a waste of money since it does no good.

What If A Cat Is Found To Have Felv On The Routine Blood Test?

If a cat is positive on the Felv test we recommend a follow-up test in 3-4 weeks. This is because the cat could be one of those individuals who is able to rid their body of the virus (called a transitory viremia). A follow-up test will help to tell if this is the case.

How Old Should My Cat Be Before Being Given The Feline Leukemia Vaccination?

We recommend the Feline Leukemia test and vaccination for any cat (or kitten) 9 weeks of age or older.

Is It True That A Kitten Can Be Born With Feline Leukemia?

Yes. It is not uncommon for a kitten to acquire Feline Leukemia from the mother while still in the womb. Most of these kittens are "poor doers" and many of them die before 6 months of age. Sometimes however, a kitten can initially appear perfectly normal and still be carrying Felv. These kittens also usually die very young.

In The Above Discussion You Have Not Mentioned Leukemia As One Of The Main Complications With Feline Leukemia Infection. Why Is This Since The Name Of The Disease Is "Feline Leukemia"?

Leukemia (which is a cancer of the white blood cells) occurs in less than 25% of cats who acquire infection with the Feline Leukemia virus. The reason the Feline Leukemia virus got its name is because it was originally isolated (in the 1960's) from cats who had leukemia and for this reason it was named the Feline Leukemia Virus. After the test for Feline Leukemia was perfected, we discovered that this virus was responsible for many illnesses in cats and that leukemia was present in only a small number of these cases. By the time this was realized, however, the name Feline Leukemia was the one that everyone was using for this virus.


- Randy Walker DVM
Sun Lakes Animal Clinic
May 16,2004



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