About three quarters of the viral agents that have emerged recently in humans are considered to originate from other animals. These viruses have often evolved and spread into the human population through various mechanisms after the initial contact that resulted in interspecies transmission. However, knowledge of the initial stages of the emergence of viruses and associated diseases is still limited in many cases. Microbiological monitoring in populations at risk of transmission would provide insights into the initiation and early stages of the emergence process. Nonhuman primates (NHPs) share many genetic, physiological, and microbiological features with humans, and are potential sources of many infectious agents. This has been demonstrated for several simian retroviruses. HIV-1 and 2 are believed to have originated from chimpanzee and mangabey viruses, respectively, found in Central and West Africa. The current distribution of the various molecular subtypes of the HTLV-1 oncogenic retrovirus in Africa is mainly the result of numerous instances of interspecies transmission of STLV-1from NHP species in the distant past. Foamy viruses belong to the Retrovidae family and the Spumavirus genus. They are complex exogenous retroviruses and are very common in many animal species, including primates, cats, cattle, and horses, in which they cause persistent infections. The first aim of the work is to study the epidemiological and molecular aspects of the transmission of foamy viruses from monkeys to humans in populations at risk, such as the inhabitants (especially hunters) in the villages of the dense forests of southern Cameroon. It is an area in which NHPs are still very common, with a great diversity of species. The investigators have already shown that the prevalence of foamy viruses is very high in these monkeys and great apes (gorillas and chimpanzees). Contact between these monkeys and the villagers is very frequent, mainly during hunting. The second aim of the project is to study the clinical and biological features of infected people and investigate intrafamilial transmission from infected index cases.