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A large percentage of cats that are infected with FeLV remain clinically normal for a long period of time. Some cats will eliminate the viral infection, while others will develop a latent infection of the bone marrow that may be reactivated at a later time. Within 2 years, > 50% of infected cats will develop diseases associated with the FeLV infection. If the immune response does not intervene, the cat will develop a persistent infection. A persistently infected cat is susceptible to a variety of disorders, including tumor development, bone marrow suppression and the diseases associated with viral immunosuppression including enteritis, gingivitis, septicemia, coronaviral-induced peritonitis, pneumonia and hemotropic or parasitic diseases. Those cats that progress to the second stage of viremia from FeLV are unlikely to recover and the prognosis is poor. There is a severe decrease in the life expectancy of a FeLV positive cat. The median life expectancy for an infected cat is 3 years old. Although the virus is responsible for 33% of all cancer deaths in the cat, FeLV-induced immunosuppression leading to the onset of opportunistic secondary infections is the most common cause of death.

AAFP, 2006; Cotter, 1984; Cotter et al., 1975; Essex et al., 1975; Essex et al., 1977;
Essex et al., 1985; Gleich et al., 2009; Hofmann-Lehmann et al., 1997; Ogilvie et al., 1988