Understanding FeLV

Principal Natural Treatments: Glycoproteins such as acemannan, orthomolecular therapy

Feline leukemia virus infection is a viral infection that is spread between cats by prolonged contact with saliva or nasal secretions. Infection most commonly occurs in outdoor male cats between 1 to 6 years of age. Approximately 30% of exposed cats are persistently viremic (and remain infected), 30% are transiently viremic (infected with the virus and then cure themselves of the infection), and the remaining 40% of cats are latently infected and test negative on blood testing (the infection resides somewhere in the body such as the spleen, lymph nodes, or bone marrow but not in the blood).

Similar to infection with the FIV virus, the most typical signs seen in infected FeLV positive cats are chronic disease, such as diarrhea, skin infections, and dental disease. Cancerous tumors may also occur. Any clinical signs (such as seizures) can occur as the signs that are seen depend upon the specific body tissue infected by the virus. Cats who persistently test positive on the blood tests for the virus will usually be infected for life.



Glycoproteins are protein molecules bound to carbohydrate molecules. Glycoprotein molecules coat the surface of every cell with a nucleus in the human body. The body uses the glycoproteins on cell surface glycoconjugates as communication or recognition molecules. These communications may then result in other cellular events, including secretion of bioactive substances (interferon, interleukin-1, complement), ingestion of bacteria and cell debris, inhibition of adherence necessary for bacterial infection, and the spread of cancer cell metastasis.

Scientists have identified eight sugars, glycoforms, found on human cell surfaces that are involved in cellular recognition processes. Of the 200 such sugars occurring naturally in plants, to date only these eight have been identified as components of cellular glycoproteins. These eight sugars that are essential for glycoconjugate synthesis (mannose, galactose, fucose, xylose, glucose, sialic acid, N-acetylglucosamine, N-acetylgalactosamine) can be readily absorbed and directly incorporated into glycoproteins and glycolipids.

Recent research has found specific cell surface glycoforms to be characteristic of many disease conditions. In some patients with rheumatoid arthritis, some defense cells (IgG antibody) bear malformed glycoproteins. These cells are missing required galactose molecules; the extent to which the galactose molecules are missing correlates with disease severity and reverses in disease remission. In people with cancer, more than 20 different malignancies are known to be associated with characteristic glycoproteins.

Glyconutritional supplements are designed to provide substrates for the body to use in building part of the glycoconjugates on cell surfaces. These supplements, most commonly acemannan and mannose, are designed to make the necessary sugars available to the cells quicker and in greater quantity.

Acemannan is a glycoprotein (a long chain of mannan polymers with random o-acetyl groups) derived from the aloe vera plant that has been shown to increase the body's production of immune-modulating chemicals including interleukins-1 and 6, interferon-gamma, and Prostaglandin E and tumor necrosis factor alpha by macrophages. Acemannan also enhances macrophage phagocytosis and nonspecific cytotoxicity, which increases the ability of white blood cells (macrophages) to destroy infectious organisms. Glycoproteins such as acemannan also offer antiviral activity as well as bone marrow stimulating activity.

Scientific Evidence

Acemannan has been proposed as an adjunctive therapy for cats with feline leukemia virus infection. No definitive studies of large numbers of cats have shown the cats to revert to a negative viral status, although the administration of acemannan did appear to prolong the life of the cats. In sick cats with leukemia virus infection, 29 out of 41 cats survived a 12-week study period using intraperitoneal acemannan (2 mg/kg weekly for the first 6 weeks of the study). Two months following the 12-week study, 21 cats were still alive (1 had died, 5 cats could not be followed up as their owners had moved). In a similar study of sick cats that were leukemia positive and not treated with acemannan, 40 out of 46 cats died or were euthanized within 5 days of diagnosis.

In these studies, all cats remained virus positive but experienced a noticeable improvement in the quality of life. While acemannan (and other glycoproteins) may be helpful for cats with leukemia viral infections, more studies are needed to determine what if any true long-term benefit infected cats might experience. At the current time, acemannan and other glycoproteins such as mannose (Ambrotose) probably serve as a useful treatment option for this chronic feline viral disease for which conventional therapies really do not exist (conventional therapies are of no particular benefit and serve mainly to support the sick cat).

All eight of the glycoconjugate sugars are readily absorbed from the intestines when taken orally. Studies have shown intact mannose molecules are rapidly absorbed from the intestine of rats into the blood, elevating the blood mannose levels by 3- to 10-fold, arid mannose is cleared from the blood within hours. The conclusion reached was that mannose was absorbed from the intestinal tract into the blood and from the blood into the cells. These studies suggest that dietary mannose may make a significant contribution to glycoform synthesis in mammals.

Other human and animal ingestion studies show that mannose is readily absorbed, and is cleared from the blood over several hours; some of the mannose was incorporated into glycoproteins. After absorption into the blood, glycoconjugate sugars generally become distributed (usually as glycoproteins and glycolipids) into body fluids, organs, and various body tissues.

In one study, healthy humans were given radiolabeled galactose, mannose, or glucose. This study showed that galactose and mannose were directly incorporated into human glycoproteins without first being broken down into glucose. The conclusion was that specific dietary sugars could represent a new class of nutrients and that the use of these nutrients could have important consequences. Therapy with mannose offers a treatment that is easy to administer and is nontoxic.

Adverse effects caused by glycoconjugate sugars are rare and usually occur when they are injected or when doses greatly exceed levels that would be expected in normal diets. For pets being treated with the most commonly used glycoproteins (acemannan and mannose), side effects would not be expected.

Orthomolecular Therapy

Orthomolecular medicine (often called "megavitamin therapy") seeks to use increased levels of vitamins and minerals (mainly antioxidants) to help treat a variety of medical disorders. While daily amounts of vitamins and minerals have been recommended as an attempt to prevent nutritional deficiencies, orthomolecular medicine uses higher doses as part of the therapy for disease.

The pet food industry relies on recommendations by the National Research Council (NRC) to prevent diseases caused by nutrient deficiencies in the "average" pet; yet, the NRC has not attempted to determine the optimum amount of nutrients or their effects in treating medical disorders. While a minimum amount of nutrients may be satisfactory in preventing diseases caused by nutrient deficiencies, it is important to realize that there is no "average" pet, and that every pet has unique nutritional needs.

It is unlikely that our current recommendations are adequate to maintain health in every pet since each pet has unique requirements for nutrients. Additionally, these needs will vary depending upon the pet's health. For example, in times of stress or disease additional nutrients above and beyond those needed for health will be required. Orthomolecular medicine evaluates the needs of the pet and uses increased nutrients to fight disease.

Orthomolecular therapy of feline leukemia utilizes 750 mg of sodium ascorbate, 750 IU of vitamin A, and 75 IU of vitamin E. A number of cats on this protocol tested negative for leukemia virus within 2 years of initial diagnosis on both ELISA and IFA tests. Also, many cats displaying signs of chronic illness became devoid of symptoms. Since false negative test results are possible, all cats testing negative on blood ELISA testing treated with orthomolecular therapy should have follow-up IFA testing done.


As with FIV infection, there is no cure for FeLV infection. Clinical signs are treated, as needed; chronic infections are treated with antibiotics. Supportive care for cats with fever and lack of appetite (such as fluid therapy and force-feeding) are used as needed; human alpha-interferon may be helpful.

Excerpt from The Natural Health Bible for Dogs and Cats: FeLV used by permission of Prima Publications.
Copyright © 2001 by Shawn Messonnier, D.V.M. All rights reserved. Excerpt from The Natural Health Bible for Dogs & Cats, Prima Publishing, Roseville, CA.

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