Several hundred distinct non human primate species are recognised, and they are likely to harbour a similar range of viruses to humans. Simians such as cynomolgus and rhesus macaques, African green monkeys, and marmosets are widely used for biomedical research, but despite this extensive close contact very few simian viruses have been shown to pose a threat of infection or illness to humans.
Herpesvirus Simiae is the best recognised zoonotic hazard of simians. It is an alphaherpes virus of Asiatic macaques, which causes a mild or subclinical primary infection followed by latency in its natural host. It can be acquired by humans following a bite and causes an ascending meningoencephalitis. Less than 40 human cases have been described and the mortality rate in untreated human infections is 70%. The infection is treatable with acyclovir and extensive guidelines for managing simians and potential exposures have been developed. Ebola virus and Marburg virus have caused epizootics in cynomolgus macaques and vervet monkeys respectively, which have resulted in human infection and fatalities. However, non human primates are unlikely to be their natural host. More recently simian immunodeficiency virus and simian foamy virus have infected researchers, but infection has not been linked to illness.
Simian viruses also pose a direct threat to humans through the use of primary monkey tissue cultures in laboratory work and vaccine manufacture, indeed a significant exposure of the human population occurred when cells contaminated with SV40 a polyomavirus of rhesus monkeys were used for polio vaccine production. New medical interventions such as xenotransplantation using primate organs pose a potential risk which requires careful assessment.