Phylogeny-Directed Search for Murine Leukemia Virus-Like Retroviruses in Vertebrate Genomes and in Patients Suffering from Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Prostate Cancer

Figure 5

MLLVs have spread among vertebrates in recent evolutionary time. The approximate time estimates to the last common MLLV progenitor are based on references given in the text, and on the phylogenetic analysis of Figure 1. Some gibbon apes in captivity have gibbon ape leukemia virus (GaLV). Koalas have recently been infected with koala retrovirus (KoRV). More distant relatives of the murine MLVs occur in pigs and cats. Porcine MLLV ERVs (PERVs) are MLLVs but the interspecies transmission routes are uncertain. Cats have several endogenous and exogenous MLLVs, including feline leukemia virus (FeLV). Birds have recently been infected with reticuloendotheliosis virus (REV). REV is not strictly an MLLV, but is a gammaretrovirus highly related to MLLVs. Its origin is uncertain, but its closest relatives are the ERV-T-like proviruses from opossum and primates. Humans may also recently have been infected with murine MLLVs, namely XMRV, although there are now indications that this is a laboratory contamination with the 22Rv1 virus. Endo-: endogenous retrovirus. Exo-: exogenous retrovirus.