Survival rate, blood feeding habits and sibling species composition of Aedes simpsoni complex: Implications for arbovirus transmission risk in East Africa.

Winnie W Kamau,Nelson Menza,Rosemary Sang,David P Tchouassi,Caroline Getugi,Baldwyn Torto,Edwin O Ogola,Sheila B Agha,Gilbert Rotich,Felix Hol

doi:10.1371/journal.pntd.0010171

Abstract

Aedes simpsoni complex has a wide distribution in Africa and comprises at least three described sub-species including the yellow fever virus (YFV) vector Ae. bromeliae. To date, the distribution and relative contributions of the sub-species and/or subpopulations including bionomic characteristics in relation to YF transmission dynamics remain poorly studied. In this study conducted in two areas with divergent ecosystems: peri-urban (coastal Rabai) and rural (Rift Valley Kerio Valley) in Kenya, survival rate was estimated by parity in Ae. simpsoni s.l. mosquitoes sampled using CO2-baited BG Sentinel traps. We then applied PCR targeting the nuclear internal transcribed spacer 2 (ITS2), region followed by sequencing and phylogenetic analytics to identify the sibling species in the Ae. simpsoni complex among parous and blood fed cohorts. Our results show that Ae. bromeliae was the most dominant sub-species in both areas, exhibiting high survival rates, human blood-feeding, and potentially, high vectorial capacity for pathogen transmission. We document for the first time the presence of Ae. lilii in Kenya and potentially yet-to-be described species in the complex displaying human feeding tendencies. We also infer a wide host feeding range on rodents, reptile, and domestic livestock besides humans especially for Ae. bromeliae. This feeding trend could likely expose humans to various zoonotic pathogens. Taken together, we highlight the utility of genotype-based analyses to generate precision surveillance data of vector populations for enhanced disease risk prediction and to guide cost-effective interventions (e.g. YF vaccinations).

Highlights

Yellow fever (YF) is a re-emerging arboviral threat in Africa and South America despite availability of an effective vaccine to protect humans
Our results show that Ae. bromeliae was the most dominant sub-species in both areas, exhibiting high survival rates, human blood-feeding, and potentially, high vectorial capacity for pathogen transmission
Aedes simpsoni s.l. has the potential to serve as bridge vector, moving the YF virus (YFV) from the sylvatic/rural to the urban transmission cycle

Summary

Introduction

Yellow fever (YF) is a re-emerging arboviral threat in Africa and South America despite availability of an effective vaccine to protect humans This is unparalleled in eastern Africa exemplified by increased frequency and magnitude of outbreaks recorded recently in Sudan (2012), South Sudan (2020), Uganda (2011, 2016, 2019, 2020), and Ethiopia (2012–2014, 2018; 2020) [1,2]. Of the recognized YFV transmission cycles (sylvatic, rural, and urban cycles), outbreaks in the eastern African region have been described as sylvatic [3]. This is inclusive of the last documented YF outbreak in Kenya (1992–95) that implicated sylvatic Aedes vectors including Aedes simpsoni s.l. The distribution and relative contributions of the sub-species and/or subpopulations including bionomic characteristics in relation to YFV transmission dynamics remain poorly studied

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Results

Discussion

Conclusion