Many of the recent emerging or re-emerging viruses possess RNA genomes. The causes of viral re-emergence and emergence are diverse and involve anthropogenic, social and environmental changes. However, the capacity of the viral genome to vary is clearly a key element. In particular, RNA viruses that are able to evolve rapidly are more likely to be successful at exploiting new niches than DNA-based organisms. Some of these RNA viruses also have the ability to change their host range and to include humans. The natural history of lyssaviruses (family Rhabdoviridae), the causative agents of rabies, illustrates these points and therefore comprises a valuable study system. Further, the detection of new viruses and lyssaviruses in particular in the context of encephalitis of unknown etiology and the study of the diversity and evolution of rhabodoviruses and more specifically lyssaviruses constitute interesting and important topics to understand the natural evolution of rabies virus.