Feline Leukemia Virus (FeLV) is an RNA virus in the subfamily Oncovirinae belong to family Retroviridae was first described by W. Jarrett (et al., Nature 202:566) at University of Glasgow, School Veterinary Medicine, in 1964.
Pathogenic viruses are diseases mainly those of the families of: Adenoviridae, Picornaviridae, Herpesviridae, Hepadnaviridae, Flaviviridae, Retroviridae, Orthomyxoviridae, Paramyxoviridae, Papovaviridae, Polyomavirus, Rhabdoviridae, Togaviridae.