Risk assessment of urban yellow fever virus transmission in Kenya: is an efficient vector?

The absence of urban yellow fever epidemics in East Africa remains a mystery amidst the proliferation of in this region To understand the transmission dynamics of the disease, we tested urban (Mombasa, Kisumu, and Nairobi) mosquito populations in Kenya for their susceptibility to an East African yellow fever virus (YFV) genotype. Overall, 22% ( = 805) of the that were orally challenged with an infectious dose of YFV had a midgut infection, with comparable rates for Mombasa and Kisumu (χ= 0.35, df = 1,  = 0.55), but significantly lower rates for Nairobi (χ ≥ 11.08, df = 1,  ≤ 0.0009). Variations in YFV susceptibility (midgut infection) among subspecies were not associated with discernable cytochrome c oxidase subunit 1 gene haplotypes. Remarkably, no YFV dissemination or transmission was observed among the orally challenged populations. Moreover, mosquitoes that were intrathoracically inoculated with YFV failed to transmit the virus via capillary feeding. In contrast, dissemination (oral exposure) and transmission (intrathoracic inoculation) of YFV was observed among a few peri-domestic mosquitoes ( = 129) that were assessed from these urban areas. Our study highlights an inefficient urban population, and the potential for in sustaining an urban YFV transmission in Kenya. An assessment of urban susceptibility to other YFV genotypes, and vector potential of urban populations in Kenya is recommended to guide cost-effective vaccination.