Omondi, S. | bioRxiv Science

bioRxiv2024

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

IntroductionAttractive targeted sugar baits (ATSBs) are effective against Anopheles mosquitoes in semiarid 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. MethodsOne 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. ResultsThis 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). ConclusionThis 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.

zoology↗

bioRxiv2024

A rapid, cost-effective, colorimetric LAMP assay (CLASS) for detecting invasive malaria vector, Anopheles stephensi

Anopheles stephensi, an invasive malaria vector in Africa, has the potential to impact the landscape of malaria on the continent, threatening to put an additional 126 million people per year at risk of malaria, largely in peri-urban/urban areas. To accelerate the early detection and rapid response to An. stephensi and ensure no gains made in malaria control and elimination are lost, it is critical to confirm the presence of the species and the geographic extent of its spread to inform control. However, morphological identification may be misinterpreted if specimens are damaged and existing molecular species confirmation assays require specialized laboratory equipment and training and may be challenging to interpret, requiring additional sequencing confirmation. A colorimetric rapid loop-mediated isothermal amplification (LAMP) assay for molecular An. stephensi species identification was developed and optimized. The colorimetric assay requires only a heat source and reagents and can be used with or without DNA extraction resulting in positive color change in 30-35 minutes. To determine analytical sensitivity, a 1:10 dilution series of the DNA extract was conducted showing 100% assay sensitivity down to 0.003 nanograms. To determine specificity, three different An. stephensi laboratory strains (STE2, SDA 500, UCI), 8 other Anopheles mosquito species, and Aedes aegypti were compared, and the results indicated 100% specificity across these species. To determine use without the need for DNA extraction, samples evaluated included a single mosquito leg, whole adult or larval mosquitoes, and pooled DNA extract from several mosquito species. A total of 1687 individual reactions were tested during optimization and all LAMP assay results were compared against the conventional PCR assay and confirmed through Sanger sequencing. To validate the optimized assay on wild caught specimens, DNA extracted from 12 wild caught, sequence-confirmed An. stephensi from Marsabit, Kenya, were tested and the colorimetric assay was accurate in identifying all of the specimens as An. stephensi. The assay described presents an opportunity to accelerate An. stephensi molecular identification in new and existing locations in Africa, within its endemic range, and globally. These findings present a simple, rapid, unique alternative to existing PCR and sequencing-based An. stephensi species identification and confirmation strategies. With additional field validation studies, molecular screening tools like the colorimetric LAMP-based An. stephensi species identification (CLASS) assay fill an important gap of rapid confirmation of this invasive vector and presents an ideal opportunity to better understand the spread of the species in Africa and other recently invaded areas, thus accelerating a response to mitigate its long-term impacts on malaria on the continent.

molecular biology↗