Genetic diversity of Anopheles stephensi in Ethiopia provides insight into patterns of spread

Abstract

Background The recent detection of the South Asian malaria vector Anopheles stephensi in the Horn of Africa (HOA) raises concerns about the impact of this mosquito on malaria transmission in the region. Analysis of An. stephensi genetic diversity and population structure can provide insight into the history of the mosquito in the HOA to improve predictions of future spread. We investigated the genetic diversity of An. stephensi in eastern Ethiopia, where detection suggests a range expansion into this region, in order to understand the history of this invasive population. Methods We sequenced the cytochrome oxidase subunit I (COI) and cytochrome B gene (CytB) in 187 An. stephensi collected from 10 sites in Ethiopia in 2018. Population genetic, phylogenetic, and minimum spanning network analyses were conducted for Ethiopian sequences. Molecular identification of blood meal sources was also performed using universal vertebrate CytB sequencing. Results Six An. stephensi COI-CytB haplotypes were observed, with the highest number of haplotypes in the northeastern sites (Semera, Bati, and Gewana towns) relative to the southeastern sites (Kebridehar, Godey, and Degehabur) in eastern Ethiopia. We observed population differentiation, with the highest differentiation between the northeastern sites compared to central sites (Erer Gota, Dire Dawa, and Awash Sebat Kilo) and the southeastern sites. Phylogenetic and network analysis revealed that the HOA An. stephensi are more genetically similar to An. stephensi from southern Asia than from the Arabian Peninsula. Finally, molecular blood meal analysis revealed evidence of feeding on cows, goats, dogs, and humans, as well as evidence of multiple (mixed) blood meals. Conclusion We show that An. stephensi is genetically diverse in Ethiopia and with evidence of geographical structure. Variation in the level of diversity supports the hypothesis for a more recent introduction of An. stephensi into southeastern Ethiopia relative to the northeastern region. We also find evidence that supports the hypothesis that HOA An. stephensi populations originate from South Asia rather than the Arabian Peninsula. The evidence of both zoophagic and anthropophagic feeding support the need for additional investigation into the potential for livestock movement to play a role in vector spread in this region. Graphical Abstract

Wolbachia 16S rRNA haplotypes detected in wild Anopheles stephensi in eastern Ethiopia

“…Each sample is colored by Wolbachia haplotype, where haplotype 1 is colored in blue, haplotype 2 is colored in red, and haplotype 3 is colored in yellow. Haplotypes 1 and 2 are representative of Wolbachia supergroup A, and haplotype 3 is representative of supergroup B. Anopheles stephensi COI haplotypes are designated on the clades that they represent according to Carter et al [ 45 ]. Anopheles maculatus was used as an outgroup (KT382822).…”

Anopheles stephensi in Africa requires a more integrated response

“…Phylogenetic analysis of samples collected in the Horn of Africa suggest it may have originated in southern Asia and the Arabian Peninsula. Studies in Ethiopia have found evidence of high genetic diversity and geographical structuring, and concluded that the populations found in south-eastern parts of the country were more recent than those in the north-eastern areas [ 31 ]. This report, together with an earlier analysis concluded that An.…”

“…This report, together with an earlier analysis concluded that An. stephensi populations in this region were closely linked to samples from Pakistan, and therefore most likely originated from south Asia as opposed to the Arabian Peninsula [ 2 , 31 ]. In eastern Ethiopia, even samples collected far inland were often found along transport routes [ 19 ], suggesting that the geographical dispersal may be driven by human activities and that there may be a common origin.…”

“…stephensi is rapidly spreading within Africa. Though this data is limited to national borders, the extensive geographical spread in Ethiopia [ 19 , 31 ] and Sudan [ 5 ] are evidence that the vector species could already have domiciled in many sites distant from the initial port of entry. In the case of Sudan, where An.…”

Blood meals from ‘dead-end’ vertebrate hosts enhance transmission potential of malaria-infected mosquitoes

“…However, in most of these studies, mosquitoes were offered additional blood meals from the same host species as the original challenge (e.g., human for primary and additional blood meals) (reviewed in [3] but see [6]). While proximity to livestock is a well-known risk factor for malaria incidence, surveillance of natural populations of mosquitoes routinely finds evidence of blood from multiple host species while co-incident with human Plasmodium infections [7][8][9][10][11][12][13]. However, it is generally assumed that the nutritional benefits of a non-human blood meal can enhance vectorial capacity by promoting vector survival and population density [14][15][16][17][18][19][20], although it is unclear if it can influence parasite development rates directly.…”