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Leukemia in Cats

Feline leukemia virus (FeLV) is a fatal infectious retrovirus that affects the immune system, and can cause some cancers and associated diseases. Although it is similar to the virus that causes feline immunodeficiency disease (FIV) and the virus responsible for human AIDS (HIV), studies so far indicate that it cannot be passed on to other animals or to humans. FeLV causes lymphosarcoma, also known as feline leukemia, a cancer of the lymph nodes.


Feline leukemia is the greatest killer of cats after accidents; 21% of sick cats brought to veterinarians have leukemia. Thirty percent of all malignant cat tumors are a result of the feline leukemia virus. It afflicts both males and females, usually from one to five years old. The virus can be transmitted through the saliva, tears, urine, and feces of infected cats, and it requires close, prolonged contact to spread. Warmth and drying deactivates it.

Cats can pass it on to each other through bites, grooming, and sharing water and food bowls and litter pans. Blood-sucking insects such as fleas and mosquitoes may transmit FeLV from cat to cat. It is not transmitted via air.

Although about 70% of cats are exposed to the virus in their lifetimes, almost all recover, showing little if any signs of illness. The weak have a harder time fighting it off, and multicat households are also at risk. Kittens can contract the virus in the womb, or through the milk of a carrier mother. Some cats can harbor FeLV for years without showing signs of disease; therefore all kittens in a litter should be tested.

Cats that develop antibodies to the virus through the feline leukemia vaccine do not get sick. These cats can usually live a normal life. But in some cases, the virus may remain for a period of time somewhere in the body. It’s possible that FeLV may cause disease at a later date, if the cats are stressed or medicated with drugs that suppress the immune system.


The three forms of feline leukemia are chest, abdominal, and multicentric. The signs that the cat shows depend on the lymph nodes and organs involved.

Chest symptoms include enlarged chest lymph nodes, compressed windpipe and esophagus, fluid accumulation in the chest, breathing difficulties, coughing, and gagging.

In abdominal leukemia, malignant cells may be present in the intestine, lymph nodes, liver, spleen, or kidney. There may be a decrease in appetite, depression, weight loss, dehydration, vomiting, diarrhea or constipation, anemia, and jaundice.

Multicentric leukemia causes greatly enlarged lymph nodes under the skin and tumor formation in many organs. The cat may or may not have a fever.


Feline leukemia begins with infection of the mouth tissues. It spreads from the mouth by blood cells and infects the lymph glands. At this stage, most cats are able to block the infection. If it invades the bone marrow, the cat is infected for life. It then spreads through the blood through the circulation. Tissues such as the tear glands, salivary glands, and urinary bladder become infected. The cat is now shedding the virus, and becomes infectious to other cats.


Other conditions that may be caused by FeLV include: blood in the stool, decreased stamina, immune suppression, bleeding disorders, excessive drinking and urination, abortion, infertility, “infant mortality complex” (the unexplained deaths of newborn kittens), arthritis, ulcers at body openings (i.e., mouth, anus, vagina, and eyes), immune diseases like inflammatory bowel disease, cystitis, cloudy eyes, and neurologic abnormalities.


To prevent FeLV infection, recommendations are to keep cats indoors and away from strays who might be carrying the virus. Traditional veterinarians advise vaccination, while holistic practitioners believe that the viruses in the vaccination will only weaken the immune system, particularly in cats already infected with FeLV.

Several vaccines are available which are produced by different methods but give the same protection. However, they are not 100% effective in preventing FeLV infection. Some vaccinated cats may become temporarily FeLV-positive after exposure to the virus, but they will not develop the disease. Although most cats experience no reaction to a vaccine, some may display malaise for a few hours to two days after the shot. The relatively rare allergic reaction can be easily treated. Kittens should be vaccinated twice: first at nine to ten weeks, then three to four weeks later. Annual booster vaccinations are also recommended. Because the FeLV vaccines are not foolproof, FeLV-positive cats should not be housed with FeLV-negative cats, even if the latter have been vaccinated.


There is presently no cure for feline leukemia; it can only be controlled toward optimal quality of life and survival time. Many holistic veterinarians recommend specific supplementation, a raw meat diet, high doses of vitamin C, pureed raw liver, and homeopathic treatments, all of which can work together with standard treatments including chemotherapy, antiviral agents such as interferon, blood transfusions, and steroids. Antiviral agents may reduce the amount of virus present in the blood of the cat, and they are easier on the body than chemotherapy. Steroids may decrease the number of cancerous lymphocytes in the blood, but they can also depress the immune system and make the cat vulnerable to other diseases. All of these modalities can put a cat in remission, but it will not get rid of the virus.

Euthanasia is another way to control FeLV. But it may not be necessary, if all the cats in a household are FeLV-positive, or if it is a one-cat household. However, the FeLV-positive may eventually become very ill, and euthanasia may be the humane course of action.

After the death of a cat with leukemia, it is strongly advised that you throw away its food and water bowls, litter pans, and bedding, and clean the house thoroughly with ordinary household cleaners. If you wish to bring a new cat into the household, wait thirty days before doing so to ensure that any residual virus has died.

In a multicat household, any remaining FeLV-negative cats should be vaccinated and retested every three to six months for the next year; any that become positive during that time should be removed. All the cats must test negative in two tests, three months apart, before the household can be considered FeLV-free. New cats should test negative initially, then be quarantined for at least two months; after that period, they should retest FeLV-negative before they’re allowed to come into contact with the other resident cats.


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