Epidemiology of feline leukaemia virus infections.

In cats the commonest cause of leukaemia and lymphomas is infection with feline leukaemia virus (FeLV). Following infection with this retrovirus some cats eliminate the virus and produce neutralizing antibody whereas others remain latently infected. A final group become persistently infected, and eventually succumb to neoplastic or non-neoplastic diseases induced by the virus. The proportion of cats falling into these different post-infection states depends on the age of exposure and the dose of virus received. In breeding colonies where the virus is endemic, up to 40% may be persistently infected, whereas in surveys of urban or suburban cats, only 1% are found to be infected for life. An important epidemiological feature of FeLV infection is that the majority of cats die from anaemia or immunosuppression rather than from leukaemia. Recent studies of the molecular biology of FeLV have shown that T cell tumour induction involves either transduction or insertional mutagenesis of the myc gene. Recombination between FeLV and FeLV related sequences present in all cat cells also appears to be important in generating different subgroups of the virus.