Simian retrovirus (SRV) is a species of retroviruses that usually infect and cause a fatal immune deficiency in Asian macaques. This virus appears sporadically in captive macaques at breeding facilities which expected as the natural host, but prevalence of this virus in feral macaques remain unknown. SRV was transmitted naturally by virus-containing body fluids (saliva, urine, blood, etc.), via biting or scratching.