Causative Agent:
Feline leukemia is caused by the feline leukemia virus (FeLV) which results in severe life-threatening disease in cats.Clinical Signs:
FeLV can cause disease and death in a variety of ways. The virus can directly cause certain types of cancer to occur. Among these are leukemia (the disease which has given the virus its common name) and lymphoma. Both of these cancers are associated with the circulatory and lymphatic systems of the body. These systems are widely distributed throughout the body, therefore, clinical signs of disease may involve any other body system. Cancer growth may occur in the chest, head, brain, skin, liver, stomach, intestines, urinary bladder, kidneys, spinal cord, or lungs. Clinical signs related to any of these areas may occur and include difficulty breathing, vomiting, diarrhea, weakness, weight loss, lack of appetite, seizures, anisocoria (unequal size of the pupils), hematuria (blood in the urine), paralysis, sneezing, and behavior changes.FeLV also causes disease in forms which are non-malignant (unrelated to cancer). The most prevalent among these are immunosuppression (weakening of the immune system) and anemia. When compared to healthy cats, those cats with FeLV are more susceptible to infections. These animals should be kept away from sick cats and from roaming outdoors in general. Cats with anemia may require intensive care to keep it under control.
Disease Transmission:
The virus is spread from animal to animal mainly through saliva. Although less likely, transmission may occur from infected cats to others through urine, feces, and insect bites. It may also spread from mother to offspring during pregnancy. Most kittens born to an infected queen, however, become infected themselves when they are nursing. It is important to realize that any infected cat sheds the virus, whether the infected cat is actually sick or not. Transmission is very unlikely in a boarding facility or hospital setting, as long as direct contact between the infected cat and others is avoided. The virus is very unstable outside of the body; therefore, it is not necessary for an owner to wait a long time to adopt a new cat or kitten after removal of a cat infected with FeLV.Diagnosis:
The most common techniques for diagnosing a FeLV infection in cats are FA (fluorescent antibody) and ELISA (enzyme-linked immunosorbent assay). Both techniques detect a specific protein in the core of the virus. ELISA tests are available for in-hospital testing and require a few drops of blood and about 10 minutes. See page D228 for more information on this test. In many cases, it is helpful to perform both tests to determine an individual’s prognosis. The specific diagnosis of cancer or secondary infections resulting from FeLV requires other diagnostic testing specific to the situation.Treatment: There is no known "cure" for a FeLV infection. A percentage of cats diagnosed with the virus will become negative on future tests, although they may not completely eliminate the virus from their bodies. Generally speaking, this is a good sign for the future of the cat, although some cats may still succumb to the virus even after they change from testing positive to testing negative.
Some anti-viral medications have been used experimentally. Interferon products, zidovudine, acemannan, and passive antibody therapy have all been attempted; more research is required before these potential treatments are fully understood. Passive antibody therapy has been successful in eliminating FeLV in cats if the exposure occurred within 3 weeks of the treatment.
Medications that help prolong the life span of red blood cells (i.e. prednisolone), that stimulate the production of more red blood cells (i.e. erythropoietin), and replace lost red blood cells (i.e. blood transfusions) can be used to treat cases of anemia. Treatment of secondary infections resulting from immunosuppression involves identifying the exact cause of the infection and selecting the appropriate antibacterial, antiviral, antifungal, or antiparasitic therapy.
Treatment of cancer secondary to FeLV infections is probably the most complex and expensive of the therapies available. Many cats with lymphoma can be helped with chemotherapy and sometimes surgery. Bone marrow involvement tends to decrease the chances of success. Untreated, lymphoma is usually fatal within 2 months; however, with treatment, some cats may live for 2 or more years. Chemotherapy is available for leukemia, but complications are very common and may be extremely severe.
Prevention: Avoiding exposure is the most effective method of prevention. Individuals which live indoors in one- or two-cat households are at a minimal risk of infection. Individuals which live in multi-cat households and spend time outdoors tend to run higher risks for infection with FeLV.
Vaccines are available for prevention of FeLV. It is difficult, however, to measure the actual effectiveness of these vaccines in live animals. No vaccine is 100% effective and avoiding exposure should still be attempted in all vaccinated cats.
Public Health Concerns: Some studies have shown possible evidence of a connection between human leukemia and FeLV. However, it is difficult to interpret this information in a practical manner. No human has ever been diagnosed with FeLV infection and no case of human leukemia has ever been definitively linked with a FeLV. It is generally accepted that FeLV does not appear to be a human health hazard.