Abstract
BackgroundSelection of blood meal hosts by mosquitoes is a key variable in the vectorial capacity of Anopheles mosquitoes for human malaria. Blood feeding on humans is likely to be modulated by use of different types of long-lasting insecticidal nets (LLINs) and the effectiveness of LLINs is impacted by the relative intensity of insecticide resistance. The aim of this study was to test the hypothesis that LLINs containing pyrethroid and the synergist piperonyl butoxide (PBO) would lead to a reduction of human host utilization than LLINs containing only pyrethroid and that blood feeding patterns of Anopheles in Malawi compromise malaria interventions.MethodsFemale Anopheles mosquitoes were sampled indoors from May 2019 through April 2020 by aspiration, pyrethrum spray catch, and CDC light trap in rural villages of Namanolo (conventional nets) and Ntaja (PBO nets) in Balaka and Machinga districts respectively. Anopheles species, blood meal sources, and infection with Plasmodium falciparum in the head and thorax of individual mosquitoes were determined with PCR.ResultsOf a total of 6,585 Anopheles females sampled indoors in 203 houses, 633 (9.6%) were blood-fed and consisted of An. arabiensis (44.1% (n = 279)), An. gambiae s.s (16.2% (n = 103)), An. funestus s.s (33.5% (n = 212)), An. parensis 0.3% (n = 2), and unidentified Anopheles spp (5.8% (n = 37)). Of the 541 mosquitoes (85.5%) successfully identified blood meals, 436 (81.0%) were solely human, 28 (5.2%) goat, 11 (2.0%) dog, 60 (11.1%) mixed goat-human, 5 (0.9%) dog-human, and 1 dog-goat. Human blood index and EIR was high in Namanolo than Ntaja (0.96 vs 0.89 (p = 0.001) and 0.11 vs 0.06 infective bites per person per year respectively) despite high net ownership (92%) and nightly use (75%) rates. Relative to host availability, non-human hosts were over selected in the two sites.ConclusionThe use of PBO nets was associated with lower HBI and EIR, however, the wide availability of LLINs was still associated with extensive successful human blood meals by the main malaria vectors in Malawi. The presence of a small fraction of mixed blood meals indicates constrained plasticity of Anopheles vectors to switch to non-human hosts and circumvent malaria control interventions.