Species composition and blood feeding patterns of understudied Anopheles mosquitoes in southern Zambia, an area of low malaria transmission

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BACKGROUND: Understanding the composition, host feeding patterns, and infection status of all potential vectors is essential to understand changing disease transmission dynamics and inform future vector control strategies. This study assessed anopheline species composition, abundance, distribution, and host feeding preferences in Southern Province, Zambia to identify potential contributors to residual malaria transmission beyond primary vectors. METHODS: Adult mosquitoes were collected along a 100 km transect between the districts of Pemba, Monze and Gwembe in Southern Province, Zambia, an area of low malaria transmission. Mosquitoes were sampled from 12 randomly selected households at 5 km intervals along the transect. Centers for Disease Control and Prevention light traps were used to collect adult mosquitoes indoors and outdoors. Mosquitoes were identified using morphological keys and molecular approaches. A multiplexed PCR assay was utilized to identify mammalian hosts and Plasmodium falciparum (Pf) sporozoite infection was determined using an enzyme linked immunosorbent assay. RESULTS: A total of 5697 female anopheline mosquitoes were collected from both indoor and outdoor traps, revealing a diverse range of species. Nine species of Anopheles mosquitoes were identified, dominated by Anopheles rufipes (n = 1527, 26.8%), and An. pretoriensis (n = 1427, 25.1%). Host blood meal analysis of 401 visibly blood-fed mosquitoes revealed that Anopheles species in the study area fed primarily on goats (n = 176; 62.5%), humans (n = 55; 19.4%) and cows (n = 29; 10.2%). The human blood index across all captured anophelines was estimated at 0.22. Human blood meals were detected in secondary malaria vectors, with notably high HBI values of An. pretoriensis and An. rufipes mosquitoes captured outdoors near goat pens. Out of the 5697 female anophelines tested for sporozoite infectivity, one An. rufipes specimen was positive for P. falciparum. CONCLUSION: This study demonstrates that malaria transmission risk in the surveyed areas may extend beyond well-recognized primary vectors. Species that are not well studied, often exophagic and assumed to be zoophagic, were found to have fed on humans and the study showed some preliminary evidence of P. falciparum infectivity. These findings indicate that peri-domestic human activity may sustain residual transmission despite high Insecticidal-Treated Nets and indoor residual spraying coverage.

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