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Feline Leukemia Virus (FELV)
FeLV is a very serious disease of the feline world was first diagnosed in the 1960's. Many cats that get exposed to the virus develop antibodies and are able to fight it off. This is especially true for cats that are free of parasites, are current on their routine vaccines, and are fed a good diet. Cats that have minimal exposure to other cats are at significantly less risk of getting this disease. Humans and dogs do not get this disease, nor do they get FIV.
Cause
It is caused by a retrovirus (FIV is also caused by a retrovirus) that is spread from cat to cat by saliva and respiratory secretions. It is found in the urine, but this is not readily transmitted this way.
The virus does not live more than a few hours outside a cats body unless it is in a moist environment, like a water bowl. This means that cats that share litter pans and feeding bowls, along with cats that fight, are at risk. Kittens born to mothers that have the virus are infected in the womb.
Stages
The whole process from initial infection to the shedding of the virus in body fluids takes from 2-6 weeks.
1. The virus replicates in the lymphatic tissue in the oral cavity.
2. If the immune system is not able to stop the problem at this stage, the virus spreads to white blood cells that circulate in the body.
3. These white blood cells spread the virus to lymph nodes in the rest of the body. Most cats ( 60-80%) make antibodies at this stage to prevent further replication of the virus.
4. If these antibodies are not made, the virus spreads through the circulation to the bone marrow, where it will remain for the rest of the cats life.
5. White blood cells and platelets that are normally made in the bone marrow pick up this virus and bring it back into the circulation.
6. The virus is spread to the salivary glands, the tear glands, and the urinary bladder. It is at this stage that the virus can be shed and infect other cats.
To summarize, several outcomes are possible if your cat is exposed to this virus:
- It makes antibodies and fights off the virus
- It becomes a carrier of the virus without showing any symptoms initially. These cats can spread the virus to other cats easily because they show no signs of illness. After a variable period of time these cats will probably develop one of the diseases associated with the virus.
- The virus weakens the immune system and various problems of a chronic nature (anemia, infections, etc.) develop.
- It causes a serious cancer of the lymph nodes, called lymphoma or lymphosarcoma. This is why it was called Feline "Leukemia" Virus when first discovered.
It is not understood why some cats can make antibodies to FeLV and never get it, while others succumb to the virus. Many factors are postulated to be involved, including stress, diet, and of course, genetics.
Symptoms
There are no specific set of symptoms that tell us for certainty that a cat has FeLV. Cats that have this virus will commonly have fevers (>103 degrees F), poor appetites, are lethargic, suffer from recurring infections, and will have experienced weight loss. Some even have skin conditions. The ability of this virus to cause immunosupression makes cats more susceptible to Demodex and Scabies.
These symptoms are quite variable though, and are also present with other diseases like hyperthyroidism, liver disease, sugar diabetes, kidney disease, and feline hyperthyroidism, so a correct diagnosis is important. Cats that are carriers of the disease may not have any symptoms.
An occasional cat with FeLV will have uneven pupils, called Anisocoria
Cats that have FeLV are susceptible to other diseases, notably FIA (Feline Infectious Anemia). FIA is caused by a blood parasite called Hemobartonella. This parasite will either cause anemia by itself, or worsen the anemia caused be FeLV.
Several disease syndromes are associated with this disease, especially since the virus is immunosuppressive:
Anemia can occur because the virus attacks the bone marrow and prevents the production of red blood cells. Anemia is diagnosed by a blood sample that counts the red blood cells. Pets that are anemic tend to be lethargic and have poor appetites. Cats that are anemic due to FeLV need their red blood cells checked every 3 months on a routine basis. Fortunately, this test is inexpensive and can be performed in our hospital in a few minutes. This report from our laboratory is from a cat that is very ill with FeLV. The white blood cells (WBC) and red blood cells (RBC) are very low. The low WBC helps verify that this cat indeed does have a virus that is effecting, and also warns us that this cat is susceptible to secondary bacterial infections.
Chronic wounds or infections are another common problem associated with FeLV. This occurs when the virus again attacks the bone marrow like in anemia, but this time it effects the white blood cells. White blood cells are needed to fight an infection. Symptoms of this problem could be lethargy, poor appetite, swelling, draining wounds or soreness when petted. This is a chronic non-healing infection on the front leg of a cat, typical of a cat that is immunosuppressed.
Malignant cancer of the lymph nodes occurs on occasion. This is a serious complication of the disease and requires specialized medical and surgical care. Pets with this syndrome of the FeLV virus might show signs of weight loss, have poor hair coats and poor appetites. This surgeon is holding an enlarged popliteal lymph node just prior to surgical removal for analysis. The popliteal lymph node is located on each of the rear legs opposite the knee.
Malignant cancers of internal organs in the abdomen. These are not usually diagnosed until they have grown significantly, verifying the importance of routine exams of FeLV positive cats.
This tumor was in the small intestines. Associated diseases like FIA can occur due to immunosupression. This is a parasite of the red blood cells that can worsen the anemia that might already exist. It is treated with the use of special antibiotics, but may be difficult to control due to the effect the FeLV has on the immune system.
Diseases of internal organs like the liver, kidneys, brain, lung, GI tract, and eyes are also associated with FeLV. Diseases of these organs are also treated with symptomatic care.
Treatment
Over the year many different "concoctions" have been tried to treat FeLV (along with FIV and FIP), some with great claims of success. With the advent of the Internet these miracle cures spread rapidly, and since they are in print, somehow have great credibility. With new antiviral medications as a potential to treat viruses in the near future one day these claims may ring true. Until then, it is best to follow the treatment plan that your veterinarian recommends.
Also, any treatment has the potential to cause other problems. For example, in humans, it is very common to take megadoses of Vitamin C (ascorbic acid). Claims abound about how it cures or prevents the common cold (which is caused by a virus). Unlike people, cats can manufacture their own ascorbic acid, so it is not mandatory in the diet like it is in people. To further complicate the issue, something as seemingly harmless as large doses of this water soluble vitamin are one of the potential causes of bladder stones in animals.
There is no current medication that will kill this virus. Treatment is aimed at keeping the immune system as strong as possible and utilizing medication as needed. In reality, we are treating the symptoms of the secondary diseases that occur because of the immunosupression caused by the virus.
As in other viruses, the symptoms associated with FeLV can wax and wane, so it is usually advantageous to treat for several days to help a cat get over what is hopefully a temporary episode. Some of the more common treatments include:
Antibiotics
Are commonly used to help these immunosuppressed cats fight off bacterial infections. The blood sample above showed a cat with a very low white blood cell count due to the virus. This cat is more susceptible to infections because of this.
If Hemobartonella (FIA- Feline Infectious Anemia) is present in the bloodstream, a special antibiotic will be used to help suppress it.
Immune Stimulators
Medication can be given that can help boost the immune system. Their effects are variable and usually are worth trying in some cases. Immunoregulin and interferon are the common medications here.
Immunoregulin is an intravenous medication made up of a killed bacteria that helps stimulate the immune system.
Cortisone
The most common form of cortisone used in cats with cancer from FeLV is prednisone. It can help reduce the size of a solid tumor (lymphosarcoma) and decrease the number of circulating cancerous cells in a cat with leukemia. Unfortunately, the mechanism that allows prednisone to cause these cancers to temporarily improved also suppresses the immune system to the point that the cat is now much more vulnerable to secondary bacterial infections.
Vitamins
These cats do not eat well and can become anemic, so supplementing with B-complex vitamins might be of some benefit. A high quality cat food should also be fed. assist feeding should be utilized in cats that are not eating anything at all.
Fluids
Cat with fevers and those not eating well will routinely become dehydrated. Giving fluids will substantially help these cats fight off some of the FeLV associated diseases. They will also help counteract the fever that commonly accompanies this virus and also when secondary bacterial infections have set in.
Red Blood Cell Stimulators
A hormone called erythropoetin can be supplemented to help minimize anemia. Unfortunately, the body might eventually makes antibodies to this oral medication and the anemia returns, sometime in a more severe form. Use of this medication requires adhering to specific protocols and close monitoring.
Blood Transfusions
These can be extremely beneficial in anemic cats that are not producing adequate RBC's due to the virus. It must be fully understood though that this is only a temporary measure.
Appetite Stimulants
Some medications, especially a drug called Periactin (cyproheptadine) can increase the appetite in some cats.
Anabolic Steroids
These medications might help counteract anemia, increase appetite, and promote on overall feeling of well being.
TLC
A warm peaceful environment with plenty of attention are extremely beneficial.
Cats that are positive for the FeLV and are normal acting present a dilemma. These cats have a chance of dying from this virus in several years, and are the potential source of infection for other cats, yet they are perfectly normal otherwise. If the positive cat lives alone, and will not go outside, then it is reasonable to take the watch and wait approach. Much of the decision on these cats depends on the individual circumstances of your household, especially how many other cats you have. FeLV positive cats should never be allowed to roam outside. These cats should not be bred since there is a great likelihood of passing the virus to the kittens.
Prevention
Cats that are FeLV positive should not be allowed to breed, roam or contact other cats. Keep food bowls and utensils of positive cats away from all other cats, and clean them with bleach. Replace all bedding, food bowls, litter pans etc. when bringing in a new cat to a household that has had an FeLV positive cat.
If one or more cats in a multi cat household is positive they should be removed. The remaining negative cats should be checked every 3-6 months, and if positive, be removed from the house. Do not bring a new cat (make sure it is negative of course) into a household that has a history of cats positive unless the remaining cats are negative on 2 successive tests. Wait at least one month before introducing this new cat into the household.
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