Animal Welfare Professionals

Background- Feline leukemia virus (FeLV) is a retrovirus related to murine leukemia virus that has existed among feral cats for tens of thousands of years before its discovery in 1964 (Jarrett, et al., 1964). FeLV infection occurs mainly among cats under 3-8 years of age (reviewed Pedersen, 1998, 1991). The main source of infection is cats in the asymptomatic stage of infection. Virus is shed in all body excretions and secretions and spread is by close contact (Pedersen et al., 1977). FeLV infection in nature usually occurs after cats are old enough to socialize and the primary phase of infection is either inapparent or transient and ends with a long-lasting immune response in 95% or greater of cats. Only a small proportion of infections in nature lead to a chronic viremia. FeLV-associated diseases occur predominantly in the small group of cats with persistent infection.

FeLV disease in feral cats raised no alarms prior to its discovery and any associated mortality went unappreciated among the spectrum of maladies befalling feral cats. Therefore, what we know about the pathogenesis of FeLV infection in feral cats initially came from studies done in the 1970’s and 1980’s on groups of household cats and laboratory infections (reviewed Pedersen, 1998, 1991).