Distribution and Genetic Diversity of Aedes aegypti Subspecies across the Sahelian Belt in Sudan

Abstract

Aedes aegypti is the most important arboviral disease vector worldwide. In Africa, it exists as two morphologically distinct forms, often referred to as subspecies, Aaa and Aaf. There is a dearth of information on the distribution and genetic diversity of these two forms in Sudan and other African Sahelian region countries. This study aimed to explore the distribution and genetic diversity of Aedes aegypti subspecies using morphology and Cytochrome oxidase-1 mitochondrial marker in a large Sahelian zone in Sudan. An extensive cross-sectional survey of Aedes aegypti in Sudan was performed. Samples collected from eight locations were morphologically identified, subjected to DNA extraction, amplification, sequencing, and analyses. We classified four populations as Aaa and the other four as Aaf. Out of 140 sequence samples, forty-six distinct haplotypes were characterized. The haplotype and nucleotide diversity of the collected samples were 0.377-0.947 and 0.002-0.01, respectively. Isolation by distance was significantly evident (r = 0.586, p = 0.005). The SAMOVA test indicated that all Aaf populations are structured in one group, while the Aaa clustered into two groups. AMOVA showed 53.53% genetic differences within populations and 39.22% among groups. Phylogenetic relationships indicated two clusters in which the two subspecies were structured. Thus, the haplotype network consisted of three clusters.

Keywords: Aedes aegypti aegypti; Aedes aegypti formosus; Sudan; cytochrome oxidase-1 (CO1); haplotype; mitochondrial DNA.

Figure 1

Map of Sudan showing the location of two subspecies/forms of Aedes aegypti collected in 8 sites. Note all Ae. aegypti aegypti were found in the east, whereas Ae. aegypti formosus was found in the west, with the main Nile and the White Nile separating their collection sites.

Figure 2

Median-joining haplotype network tree of Ae. aegypti subspecies/populations from 8 sites in Sudan. The tree was constructed using 46 haplotype CO1 mtDNA sequences from the eight study sites of Sudan. The size of each circle indicates the frequency of the incidence of each haplotype in the study populations. Between two haplotypes there is a minimum of one mutation. The network consists of two Groups including haplotypes from both Aaa and Aaf populations.

Figure 3

Polar maximum likelihood phylogenetic tree from 140 female Aedes aegypti aegypti (Aaa) and Aedes aegypti formosus (Aaf) form eight study sites in Sudan. Different colors indicate different subspecies/forms. Note most Aaa clustered in one group (blue colored), while Aaf clustered separately (red-colored). Exceptions to this were some Aaa from Tokar and Barakat clustered with Aaf populations.

Figure 4

Results of the Mantel test on the correlation between genetic (F_st) and geographical distances (KM) of Aedes aegypti samples collected in 8 locations in Sudan.