Ecological diversity of Anopheles gambiae s.l. and insecticide resistance across refugee camps in Kenya

Abstract

Malaria remains a major threat during humanitarian crises, necessitating targeted vector control strategies informed by local vector dynamics. Between May and July 2023, we conducted larval surveys in refugee settlements across Dadaab, Kakuma, and Kalobeyei (Kenya), collecting Anopheles larvae. Genotyping of 728 specimens revealed spatial variations in species composition. Overall, Anopheles arabiensis was the dominant species (59%, n=426), followed by Anopheles coluzzii (35%, n=252), and Anopheles rufipes (1%, n=7). In Dadaab, An. arabiensis was overwhelmingly dominant (94%, n=352/374). In contrast, the Kakuma/Kalobeyei complex was characterized by the co-occurrence of An. coluzzii (72%, n=252/350) and An. arabiensis (22%, n=74/350), with An. rufipes exclusively found in Kalobeyei (7%, n=6/89) (Figure 2B). Notably, no members of the Anopheles funestus group or Anopheles stephensi were detected. However, approximately 5% of the larvae across the sites could not be resolved molecularly. High frequencies of the L1014F kdr mutation, a pyrethroid resistance marker, were detected in An. coluzzii (Kakuma: 50%; Kalobeyei: 63%) and An. arabiensis (Kakuma: 10%; Kalobeyei: 30%) populations in Turkana County. Interestingly, no kdr mutations were observed in the An. arabiensis population from Dadaab. These findings highlight significant spatial diversity in vector species composition and resistance profiles, with An. coluzzii emerging as a dominant, pyrethroid-resistant vector in the Kakuma/Kalobeyei complex. The results underscore the urgent need for targeted interventions, including resistance monitoring and alternative insecticide-based strategies, to mitigate malaria transmission risks in fragile, humanitarian settings. Further studies are warranted to address unidentified larval species and seasonal transmission dynamics. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=125 SRC="FIGDIR/small/682237v1_fig2.gif" ALT="Figure 2"> View larger version (12K): org.highwire.dtl.DTLVardef@1f3788forg.highwire.dtl.DTLVardef@1701f58org.highwire.dtl.DTLVardef@19d566org.highwire.dtl.DTLVardef@95716_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 2.C_FLOATNO Species composition of Anopheles mosquitoes in Kakuma, Kalobeyei, and Dadaab refugee camps, Kenya. (A) Overall relative abundance of Anopheles species identified by PCR and ITS2 sequencing. (B) Spatial distribution and abundance of the predominant species, An. coluzzii and An. arabiensis, across individual sampling sites. C_FIG