Assessing Anopheles species collection techniques in a low malaria transmission area: implications for vector surveillance and control

Abstract

BACKGROUND : Effective entomological surveillance is crucial for malaria control, especially in low transmission settings. This study aimed to compare the performance of three mosquito collection methods (clay pots, carbon dioxide (CO2)-baited tents, and human landing catches (HLC)) for malaria vector surveillance in the low transmission area of Nkomazi, South Africa. METHODS : From March 2019 to March 2020, adult mosquitoes were collected monthly from three different sites over five consecutive nights and mornings. Each collection method was used at each site to capture both outdoor resting and host-seeking mosquitoes. The collected mosquitoes were morphologically identified to the Anopheles genus and species, followed by confirmation using molecular PCR assays. The species composition, relative abundance, and diversity were evaluated, and statistical tests, including Kruskal–Wallis and ANOVA, were used to assess differences in abundance and diversity across collection sites and methods. A Generalized Linear Mixed Model was applied to assess the impact of various factors on species abundance. RESULTS : A total of 1337 Anopheles mosquitoes were collected, with 98.5% being females. CO2-baited tents yielded the highest number of mosquitoes (57.6%), followed by HLC (39.1%) and clay pots (3.3%). Species composition included 52.4% of the Anopheles gambiae complex and 13.6% of the Anopheles funestus group. While species richness varied significantly between collection methods, with CO2-baited tents showing the highest richness, no significant differences were observed in abundance across sites or methods. The clay pot method was associated with significantly lower species abundance compared to HLC and CO2-baited tents. Species abundance fluctuated across months, with February and November showing a higher record. Males were less prevalent than females. Additionally, species abundance was lower in Block C and Vlakbult compared to Block A. CONCLUSIONS : This study highlights the importance of choosing appropriate mosquito collection methods based on specific entomological indicators and transmission dynamics. While CO2-baited tents provided the highest species richness, clay pots, despite yielding fewer mosquitoes, are effective for capturing outdoor resting malaria vectors. These findings suggest that a combination of collection methods is essential for inclusive malaria vector surveillance, facilitating tailored strategies for effective malaria control and resource optimization.