Exploring the potential transmission of Rift Valley fever virus in North America by quantifying the relative importance of mosquito vectors and vertebrate hosts

Rift Valley Fever virus (RVFV) is a mosquito-borne zoonotic virus in the family Bunyaviridae which has spread from continental Africa to Madagascar and the Arabian Peninsula.  The enzootic maintenance and amplification of RVFV among wild and domestic animals is a known risk factor facilitating geographic expansion of arboviruses, as demonstrated by West Nile virus and Japanese encephalitis.  The establishment of RVFV in North America would have serious consequences for human and animal health and a large economic impact on livestock production.  This study used data published on RVFV vector and host competence, and mosquito feeding patterns to mathematically implicate mosquito vectors and host vertebrates that may be important to the establishment and enzootic maintenance of RVFV in North America.  We used a viremia-infectiousness relationship based on mosquito competence transmission studies to calculate a vertebrate host competence index. The vector force of infection, defined as the relative contribution of each mosquito species to transmission, was also estimated.  Finally, mosquito blood feeding patterns, mosquito transmission competence, and host competence were combined to create an index of important host vertebrates to RVFV transmission.  These procedures highlight the primary mosquito and vertebrate host species which would be involved in RVFV transmission in North America.  Moreover, this literature review highlights critical gaps in knowledge preventing us from a comprehensive meta-analysis describing the enzootic activity of RVFV in North America.  Future research should focus on improving the viremia-infectiousness relationship for key mosquito species and host competence of several North American mammal species, with particular emphasis on the order Artiodactyla.