Residual bioefficacy of Attractive Targeted Sugar Bait stations targeting malaria vectors during seasonal deployment in Western Province of Zambia

Abstract

Abstract Background The primary vector control interventions in Zambia are long-lasting insecticide-treated nets and indoor residual spraying. Challenges with these interventions include insecticide resistance and the outdoor biting and resting behaviors of many Anopheles mosquitoes. Therefore, new vector control tools targeting additional mosquito behaviors are needed to interrupt transmission. Attractive targeted sugar bait (ATSB) stations, which exploit the sugar feeding behaviors of mosquitoes, may help in this role. This study evaluated the residual laboratory bioefficacy of Westham prototype ATSB® Sarabi v.1.2.1 Bait Station (Westham Ltd., Hod-Hasharon, Israel) in killing malaria vectors in Western Province, Zambia, during the first year of a large cluster randomized phase-III trial (Clinical Trials.gov Identifier: NCT04800055). Methods This was a repeat cross-sectional study conducted within three districts, Nkeyema, Kaoma, and Luampa, in Western Province, Zambia. The study was conducted in 12 intervention clusters among the 70 trial clusters (35 interventions, 35 controls) between December 2021 and June 2022. Twelve undamaged bait stations installed on the outer walls of households were collected monthly (one per cluster per month) for bioassays utilizing adult female and male An. gambiae sensu stricto (Kisumu strain) mosquitoes from a laboratory colony. Results A total of 84 field-deployed ATSB stations were collected, and 71 ultimately met the study inclusion criteria for remaining in good condition. Field-deployed stations that remained in good condition (intact, non-depleted of bait, and free of dirt as well as mold) retained high levels of bioefficacy (mean induced mortality of 83.8%) after seven months in the field but did induce lower mortality rates than non-deployed ATSB stations (91.4% mean mortality). There was relatively little variation in corrected mortality rates between monthly rounds for those ATSB stations that had been deployed to the field. Conclusion While field-deployed ATSB stations induced lower mortality rates than non-deployed ATSB stations, these stations nonetheless retained high levels of bioefficacy with mean mortality rates of over 80% during seven months of operation in the field. The duration of deployment was not associated with lower bioefficacy. Westham prototype ATSB stations can still retain bioefficacy even after deployment in the field for 7 months, provided they do not meet predetermined criteria for replacement.