Abstract
The capacity of Rift Valley fever virus (RVFV) to spread into new territories by crossing significant natural geographic barriers, re-emerge in endemic regions after long periods of silence to cause large outbreaks in human and animal populations constitute a formidable challenge for public and veterinary health authorities as well as for scientific communities worldwide. In spite of recent advances in research on RVFV pathogenesis, molecular epidemiology, outbreak prediction, development of new diagnostic tools and vaccines, some fundamental aspects of the epidemiology and ecology of the virus remain elusive. Large outbreaks of RVF are associated with anomalous high rainfalls leading to massive flooding and the resultant swarms of competent mosquito vectors transmitting the virus to a wide range of susceptible vertebrate species. However, the exact mechanism of RVFV natural transmission during interepizootic periods remains largely unknown, including the postulated long-term virus persistence in transovarially infected eggs of floodwater Aedes mosquito species, and the role of wild mammals as reservoirs. The presence of competent mosquito vectors in countries free of RVF, the wide range of mammals susceptible to the virus, the global changes in climate, and increased animal trade and travel are some of the factors which might contribute to international spread. This presentation provides the background to the major outbreaks, molecular biology and epidemiology of RVFV, and overviews aspects of ecology, host and vector range which make the virus a potential global emerging threat.