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FeLV: Feline Leukemia Virus

Image413493Feline Leukemia (FeLV) disease is a complex disease that manifests itself in a variety of ways. FeLv is a major cause of illness and death in domestic cats. The incidence of disease increases in cats living in a multi-cat household and in free-roaming cats. Transmission of the virus is primiarlily through intimate contact with persistenly infected cats and spread through saliva, across the placenta to kittens and through the milk to the kittens. Persistently infected cats may shed as many as one million viral particles in each milliliter of saliva. Infection usually requires prolonged close contact and results from infectious saliva acquired through grooming, fighting and contamination of food and water dishes. Successful transmission is most likely under conditions of close contact.

Within weeks of exposure to FeLV, outcome of exposure is variable and can be divided into three groups. Factors that determine the outcome of exposure to FeLV include the challenge dose of virus, the duration of exposure, age, strength of the immune system and poorly defined genetic factors. Potential results of exposure include:

1) Uninfected Cats: Some cats regardless of exposure do not become infected. This is believed to be due to either an inherent resistance to infection or because of insufficient exposure time or dose.

2) Persistently Infected Cats: Approximately 30% of cats exposed develop progressive infection with persistence of the virus in the blood. This leads to FeLV-related disease after a variable disease-free interval. About 50% of these cats will die within six months of detection of infection and 80% will die within 3 years.

3) Transiently Infected Cats: Approximately 42% develop a transient infection of the blood system with the virus being eliminated 4-6 weeks after exposure. These cats that have "recovered" from transient infection usually become latent carriers for a variable period of time. In latent FeLV infection, the virus remains "asleep" within bone marrow & lymph node cells and in the majority of cats can be completely eliminated from the bone marrow within 30 months. These cats are usually asymptomatic and noncontagious. These cats cannot be diagnosed by conventional methods. On occasion, latent infections may be reactivated naturally by stress or by other immuno-stressful bacterial or viral diseases. "Awakening" of the FeLV virs may result in relapsing or persistence in the blood, with subsequent shedding of the virus in the saliva.

Clinical signs of the disease in FeLV infected cats is variable. Disease processes related to FeLV include cancer, illnesses due to theimmunosuppressive actions of the virus on bone marrow cells and illnesses that are a result in direct infection of bone marrow and lymph node cells.

How FeLV causes cancers is not known. Various types of FeLV cancers have been seen in the cat. Clinical signs of these cancers are dependent upon where the tumors are located. Example, stomach tumors may cause vomiting, anorexia and weight loss. Tumors of the intestines may cause diarrhea and weight loss, vomiting, anorexia or obstruction. Liver tumors cause icterus, weight loss and vomiting. If located in the kidney, signs of renal failure may become aparent. Tumors of the nervous system may exhibit itself with seizures, blindness, changes in behavior, paralysis and other motor deficits. Cancers of the blood system (leukemia) may be evident by anemia (low red blood cells) and neutropenia (low white cells). Often older cats with FeLV related cancers will test negative for FeLV.

FeLV causes profound effects on the body's immune system, effecting cells of the lymph nodes and bone marrow that are responsible for protecting the body from disease. This is the most important overall consequence of FeLV infection in many cats. Fever is often a presenting sign along with signs of any type of opportunistic infection. Examples include: other viral infections, fungal and bacterial infections. Typically seen in this clinic are upper respiratory infections that may be viral or bacterial related, oral infections, pneumonia and skin infections. Often there is a history of chronic and recurrent illness in FeLV infected cats. Suspect any cat that is repeatedly treated for sneezes, coughs, diarrhea, vomiting and anorexia.

In FeLV-infected female cats, any of the following can occur: infertility, abortion, stilbirths and weak kittens. FeLV tests are used to diagnose FeLV-related illnesses, to screen for asymptomatically infected cats before FeLV vaccination and to identify and eliminate FeLV infections from multi-cat households. Several different testing procedures are available. The testing procedures available in most veterinary practices is a simple blood test. Interpretation of these test can be complex and sometimes misleading, you veterinarian can explain these test and their results to you.

There is no cure for FeLV infection. Therapies are directed towards treating the symptoms and supportive care, such as antibiotics for FeLV-related infections, fluids, and nutritional support. Treatment for these cats are formulated to prolong survival in selected patients. Untreated cancers are usually fatal within 1-2 months. Anticancer chemotherapy can induce remission in many cats, but is expensive and you must remember is not a cure. Cats with anemia may benefit from a blood transfusion however, prognosis is poor although may prolong survival.

Because of the devastating consequences of FeLV infection and its prevalence in the cat population, prevention is of vital importance. Prevention measures include vaccination of cats that are at the greatest risk, this would include indoor/outdoor cats, free-roaming individuals and cats in multi-cat households.

Prior to vaccination it is recommended to FeLV test the cat but it is not strictly mandatory. There is no proven beneficial or detrimental effect from vaccinating a cat for FeLV that is already infected. All available vaccines produce less than 100% protection against FeLV; and even though vaccination may decrease the risk of infection, effective prevention also requires other measures that decrease risk of exposure. Your veterinarian can help you decide what prevention methods best fit your cats individual risks.

If you suspect your cat may have FeLV or has been diagnosed with FeLV talk with your veterinarian what measures you can take to help your cat and other cats that may be in your household.