Abstract:
The absence of urban yellow fever epidemics in East Africa remains a mystery amidst the proliferation of Aedes aegypti in
this region. To understand the transmission dynamics of the disease, we tested urban (Mombasa, Kisumu, and Nairobi)
Aedes mosquito populations in Kenya for their susceptibility to an East African yellow fever virus (YFV) genotype. Overall,
22% (n = 805) of the Ae. aegypti that were orally challenged with an infectious dose of YFV had a midgut infection, with
comparable rates for Mombasa and Kisumu (χ2= 0.35, df = 1, P = 0.55), but significantly lower rates for Nairobi (χ2 ≥ 11.08,
df = 1, P ≤ 0.0009). Variations in YFV susceptibility (midgut infection) among Ae. aegypti 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 Ae. aegypti populations. Moreover, Ae. aegypti 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 Ae. bromeliae
mosquitoes (n = 129) that were assessed from these urban areas. Our study highlights an inefficient urban Ae. aegypti
population, and the potential for Ae. bromeliae in sustaining an urban YFV transmission in Kenya. An assessment of
urban Ae. aegypti susceptibility to other YFV genotypes, and vector potential of urban Ae. bromeliae populations in
Kenya is recommended to guide cost-effective vaccination.
