Feline Leukaemia Virus

Feline leukaemia virus (FeLV) is a gammaretrovirus that causes a variety of fatal diseases including leukaemia and lymphoma in its host, the domestic cat, and occasionally in large cat species. Many cats become persistently infected and develop disease after an incubation period of several years, during which virus can be transmitted to other cats. Disease is often associated with the generation of FeLV variants with increased pathogenic potential that can arise by mutation of envelope sequences, duplication of transcriptional enhancer elements or recombination with host proto-oncogene sequences. FeLV can also produce variants by recombination with endogenous proviruses related to FeLV that are found in the domestic cat and its close relatives. The prevalence of FeLV infection has been reduced in many cat populations by isolation of infected carriers and more recently by vaccines that augment the natural ability of most cats to control infection. Key Concepts: The outcome of infection by FeLV depends on the infectious dose, age and immunocompetence of the host. Many cats achieve lifelong control, if not elimination of infection. Cats that become persistently viraemic are at risk of a variety of FeLV-related diseases after a latent period of up to several years. The common infectious form, FeLV-A can acquire altered entry receptor specificity by envelope gene mutation (to FeLV-C) or recombination with endogenous FeLV-related proviruses (to FeLV-B). FeLV envelope variants may induce fatal diseases of rapid onset including nonregenerative anaemia (FeLV-C) or wasting and immunodeficiency (FeLV-T). The oncogenic potential of FeLV can evolve by duplication of transcriptional enhancer control elements in the long-terminal repeat or by transduction of host proto-oncogene sequences. Although the immune parameters of vaccine protection remain unclear, FeLV demonstrates the feasibility of effective immunisation against the gamma retroviruses. Commercial FeLV vaccines in recent or current use include inactivated FeLV, infected cell extracts, recombinant envelope protein and live recombinant poxvirus vaccines. Keywords: retrovirus; FeLV; oncogene; transduction; endogenous retrovirus; receptor; transporter; leukaemia; lymphoma; immunodeficiency