Feline leukemia virus(FeLV) a retrovirus, so named because of the way it behaves with-in infected cells. FeLV infection is responsible for more deaths among cats than any other infectious disease. The virus affects domestic cats and occurs in some wild felines as well. After the initial infection, the virus replicates in the tonsils and pharyngeal lymph nodes. Then it spreads via the bloodstream to other parts of the body, especially the lymph nodes, bone marrow and intestinal tissue, where it continued to replicate.