Influence of mould growth and outdoor exposure on the efficacy of attractive targeted sugar baits in western kenya

Abstract

Attractive targeted sugar baits (ATSBs) are effective against Anopheles mosquitoes in semi-arid climates with low humidity. High humidity, however, promotes growth of moulds on the surface of ATSBs. The impact of mould on ATSB efficacy against malaria vectors remains unknown. This study explored how mould growth affects the performance of ATSB version 1.2 by comparing mouldy stations from exposed environments to non-mouldy stations from protected settings through laboratory bioassays with the local malaria vector, Anopheles arabiensis. One hundred ATSB stations were deployed in Asembo, Rarieda-Subcounty, Siaya County, with six samples (three mouldy from exposed locations and three non-mouldy from protected locations) collected monthly for laboratory bioassays. These were tested alongside three new laboratory-kept ATSBs and two negative controls (water only and 77% sugar solution with water) to assess mosquito feeding and mortality over 48 hours. This study found that after 12 months of outdoor exposure, the mouldiest ATSBs from exposed locations showed a non-significant reduction in Anopheles arabiensis feeding rates compared to the least mouldy ATSBs from protected locations 57.42% (95% CI: 45.64-68.85) vs. 74.40% (95% CI: 64.56-82.50), respectively (P =0.062). Mosquito mortality significantly declined on mouldy ATSBs compared to laboratory controls (95% CI: 92.23-97.48) vs. 98.70% (95% CI: 97.87-99.30) respectively (P = 0.002). In contrast, protected (non-mouldy) ATSBs showed only a slight reduction in mortality compared to controls 95.94% (95% CI: 90.42-97.46) vs. 98.91% (95% CI: 97.67-99.60) respectively (P = 0.009). This study provides evidence that environmental exposure post-deployment slightly reduced the efficacy of ATSBs in controlling Anopheles arabiensis, particularly beyond the recommended 6-month period. Although mould may have contributed to this reduction over 12 months, no significant difference was found between mouldy and non-mouldy ATSBs. However, mould invasion and community concerns highlight the need to replace mouldy stations to maintain effectiveness and safety.