TREATMENT

Eradication of FeLV at any stage is extremely difficult.  Most cats are persistently viremic at the time of diagnosis.  Treatment is mainly done to reverse the viremia or decrease the associated clinical signs.  FeLV positive cats can live without major diseases for several years.  (4)

Some steps that can be taken to mitigate the course of the disease in individual cats include:
-    Keeping infected cats indoors 100% of the time to decrease the risk of exposure to infectious agents and to prevent                  further transmission to other cats (3, 4).
-    Provide good nutrition and husbandry – avoid raw meat, eggs, and unpasteurized milk to avoid possible secondary                  infections such as salmonella (3).  
-    Thorough physical exam every six months.  Focus on skin infections, external and internal parasites, dental disease,               lymph node size and shape, eye exam, and body weight (3, 4).  A CBC and urinalysis should also be done.  
-    Neuter all infected cats to decrease stress associated with estrus and mating.  It also helps to prevent roaming (3, 4)
-    Vaccinate for other feline diseases with a killed virus (3).  
-    Owners need to watch for secondary infections – a sign of FeLV (4)

Some steps that can be taken to prevent the spread of infection in multi cat households include: (3)
-    Test all cats to verify viral status
-    Isolate positive cats from negative cats.  The risk of infection in adult negative cats is approximately 10-15% if they have          lived with the positive cat for several months.  The risk of transmission to negative cats in a household is relatively low              because they have lived together with the shedding cats and are more likely immune.  
-    Administer a FeLV vaccine to negative cats.  However, virus neutralization is not life long.  Therefore a previously                      immunized cat can become viremic.  Consider revaccinating regularly. 
-    Prevent the sharing of food and water bowls as well as mutual grooming.  

The prognosis for persistently viremic cats is guarded.  The majority of infected cats usually die within 2 - 3 years (4).  


TREATMENT OF LYMPHOMA AND LEUKEMIA

Cytotoxic drugs can be used but result in significant toxicities if wrongly administered and are considered carcinogens.  Approximately 50% of treated cats will obtain a complete remission (no clinical evidence of disease).  FeLV negative cats that attain complete remission live an average of 9 months and FeLV positive cats have average survival of 6 months, compared to cats with no treatment that live approximately 6 weeks (3).  

Combinations of chemotherapeutic drugs offer the best chance for complete remission (3).  The protocol for treatment consists of an intensive induction phase - vincristine IV weekly for 4 weeks, cyclophosphamide orally every 3 weeks on the same day as vincristine, and prednisolone orally once daily throughout the protocol.  This combination is known as COP.  This is followed by a less intensive maintenance phase – vincristine and cyclophosphamide every 3 weeks on the same day and prednisolone daily.  Treatment is continued for 1 year or until a relapse occurs.  79% of cats attained remission and an average survival of 150 days.  Doxorubicin given IV every 3 weeks can also be added (combination is called COPA) to the protocol which can extend the remission period to 281 days.  All of these drugs are immunosuppressive and some are myelosuppressive which can lead to the production of other FeLV associated diseases (4). 

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Acute lymphocytic leukemia is treated much the same way but remission only occurs in approximately 25% of cats.  Chronic lymphocytic leukemia is best treated with chlorambucil and prednisolone given every other day on alternating days.  Non lymphocytic leukemias are rarely treated because the cats are extremely ill and very few respond.  


SUPPORTIVE TREATMENT

For management of secondary infectious conditions, a more aggressive and prolonged therapy is encouraged as the cat is immunocompromised and less able to fight the disease naturally (2, 3, 4).  Supportive treatment in the form of parenteral fluids and nutritional supplements may be useful (3).  However, hematinic agents, vitamin B12, folic acid, anabolic steroids, and erythropoietin have been found to be unsuccessful in managing a non-regenerative anemia (2).  Glucocorticoids and other immune suppressive drugs should be avoided when possible unless clearly indicated for a specific problem (3).  All myelosuppressive drugs should be avoided (3).  

Passive antibody transfer can reduce the level of FeLV antigenemia (8).  This can be done by obtaining antibodies from cats that are vaccinated for FeLV (8).  However, recipients of the antibodies can develop residual circulating immune complexes that could cause adverse reactions (3).  FeLV cats may also benefit from a blood transfusion to help treat a non-regenerative anemia (2, 3, 4).  

Treatment with filgrastim, a granulocyte colony-stimulating factor (G-CSF) that causes transient responses, can be used for the treatment of a neutropenia.  However, development of dose-dependent neutralizing antibodies to filgrastim occurs after 10 days to 7 weeks.  Therefore, treatment should not be used for more than 3 weeks (3).

Cat receiving supportive therapy
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ANTIVIRAL CHEMOTHERAPY

To date, no treatment has been proven effective in clearing a FeLV infection (3).  

Zidovudine (AZT) is effective against FeLV in vitro and is somewhat effective in treating cats experimentally infected with FeLV when treated less than 3 weeks after infection.  A common side effect is a non-regenerative anemia so routine CBCs are necessary and should be performed weekly for the first month.  Owners report the cat having a fuller and shinier hair coat as a side effect (3).

Zalcitabine is effective against FeLV in vitro.  Controlled release administration has been shown to inhibit de novo FeLV replication and delay the onset of viremia (3).

Ribavirin is active against FeLV in vitro.  Therapeutic concentrations are difficult to obtain due to the toxic nature of the drug.  Cats are also very sensitive to the side effects.  Its use is not recommended (3).

Foscarnet is active against FeLV in vitro.  Side effects include nephrotoxicity and its toxicity limits its use in cats (4).


IMMUNOTHERAPY (4)

Interferon-α, interferon-ω, staphylococcus Protein A, Proprionibacterium acnes, Acemannan, Bacille Calmette-Guerin, Serratia marcescens, and Parapox virus avis and ovis have all been shown to have no real anti-FeLV effect.  Some merely improved clinical signs of the cats and reduced secondary infections.  Diethylcarbamazine (DEC) has been shown to prevent or delay FeLV associated lymphopenia and prolongs survival.  It can produce severe side effects such as hepatic injury.
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