Distribution of Anopheles mosquito species, their vectorial role and profiling of knock-down resistance mutations in Botswana

Knowledge of vector species composition and monitoring their change over time is critical to evaluate malaria transmission and assess control interventions. This is especially important in countries such as Botswana, where malaria transmission is subjected to fluctuations due to climate variability. Another important aspect that impacts vector populations is the insecticide resistance. In order to assess species composition and the presence of mutations associated with insecticide resistance, Anopheles specimens from larval samplings and indoor pyrethrum spray sheet collections were analysed. A total of 349 Anopheles were screened by morphology and PCR as belonging to the An. gambiae complex and An. funestus group. Specimens were subsequently analysed for human blood meal and Plasmodium index. Finally, knock-down resistance polymorphisms were assessed. Anopheles arabiensis accounted for the majority of specimens collected through larval (96.7%) and pyrethrum spray sheet collection (87.4%) across all sampling sites, and this species was the only one found positive for human blood and for P. falciparum. Other Anopheles species were collected in small numbers by pyrethrum spray catches, namely An. quadriannulatus, An. longipalpis type C and An. parensis. The authors speculate on changing climate patterns and their possible impact on species composition. The kdr assay revealed that Anopheles mosquitoes were homozygous wild type for both L1014F (kdr-w) and L1014S (kdr-e) mutations. These results highlight the unique vectorial role of An. arabiensis in Botswana and indicated that even with prolonged use of pyrethroids and DDT, the mosquito population has not developed kdr mutations, despite some in vivo evidence of insecticide resistance.