Implications for malaria transmission: a cross-sectional study on the bionomics and susceptibility of local malaria vectors in urban and periurban settings of Ndola district

OBJECTIVES

To assess vector behaviour and phenotypic resistance for effective vector control programming.

DESIGN

This was a cross-sectional study.

SETTING

This study was conducted in the urban and periurban areas of Ndola district, Zambia.

PARTICIPANTS/STUDY UNITS

A total of 166 houses were selected for adult mosquito collection, and an additional 60 collection efforts were made for larval collection from potential larval habitats.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome was the behaviour of the malaria vectors, and the secondary outcome was their phenotypic resistance status.

RESULTS

The main breeding sites identified were irrigation trenches (4.67 larvae/dip) and garden ponds (2.72 larvae/dip) created from extensive urban agriculture practices. Anopheles funestus sensu stricto (An. funestus s.s) and Anopheles gambiae sensu stricto (An. gambiae s.s) were found to coexist in all the four sites, with An. funestus s.s identified as the most dominant malaria vector. Densities of An. gambiae s.s, seeking a blood meal (χ2=12.566, df=3, p=0.001) and resting indoors (Z=56.5, p=0.019), were found to be higher in urban than periurban sites compared with An. funestus s.s, which had similar distribution across the study sites. Sprayed houses were significantly associated with reduced mosquito numbers (B=-0.956, incidence rate ratio=0.384, p=0.001). Anopheles gambiae was fully susceptible to organophosphates and neonicotinoids but highly resistant to pyrethroids, carbamates and organochlorines.

CONCLUSIONS

The emergence of An. funestus s.s in an area previously dominated by An. gambiae s.s and its coexistence with An. gambiae s.s in the dry season pose a risk of sustaining malaria transmission all year round. Agricultural practices in urban areas resulted in highly productive mosquito breeding sites; thus, there is a need for targeted vector control.

Microbiota Composition Associates With Mosquito Productivity Outcomes in Belowground Larval Habitats

Vector mosquitoes are well-adapted to habitats in urban areas, including belowground infrastructure such as stormwater systems. As a major source of larval habitat in population centers, control of larval populations in stormwater catch basins is an important tool for control of vector-borne disease. Larval development and adult phenotypes driving vectorial capacity in mosquitoes are modulated by the larval gut microbiota, which is recruited from the aquatic environment in which larvae develop. Laboratory studies have quantified microbe-mediated impacts on individual mosquito phenotypes, but more work is needed to characterise how microbiota variation shapes population-level outcomes. Here, we evaluated the relationship between habitat microbiota variation and mosquito population dynamics by simultaneously characterising microbiota diversity, water quality, and mosquito productivity in a network of stormwater catch basins in the Chicago metropolitan area. High throughput sequencing of 16S rRNA gene amplicons from water samples collected from 60 basins over an entire mosquito breeding season detected highly diverse bacterial communities that varied with measures of water quality and over time. In situ measurements of mosquito abundance in the same basins further varied by microbiota composition and the relative abundance of specific bacterial taxa. Altogether, these results illustrate the importance of habitat microbiota in shaping ecological processes that affect mosquito populations. They also lay the foundation for future studies to characterise the mechanisms by which specific bacterial taxa impact individual and population-level phenotypes related to mosquito vectorial capacity.

Relationships between water quality and mosquito presence and abundance: a systematic review and meta-analysis

Mosquito-borne diseases (MBDs) are emerging in response to climate and land use changes. As mosquito (Diptera: Culicidae) habitat selection is often contingent on water availability for egg and larval development, studies have recognized water quality also influences larval habitats. However, underlying species-, genera-, and mosquito level preferences for water quality conditions are varied. This systematic review and meta-analysis aimed to identify, characterize, appraise, and synthesize available global data on the relationships between water quality and mosquito presence and abundance (MPA); with the goal to further our understanding of the geographic expansion of MBD risks. A systematic review was conducted to identify studies investigating the relationships between water quality properties and MPA. Where appropriate, random-effects meta-analyses were conducted to provide pooled estimates for the association between the most reported water quality properties and MPA. The most reported water quality parameters were pH (87%), nitrogen concentrations (56%), turbidity (56%), electrical conductivity (54%), dissolved oxygen (43%), phosphorus concentrations (30%), and alkalinity (10%). Overall, pH (P = 0.05), turbidity (P < 0.0001), electrical conductivity (P = 0.005), dissolved oxygen (P < 0.0001), nitrogen (P < 0.0001), and phosphorus (P < 0.0001) showed significantly positive pooled correlations with MPA, while alkalinity showed a nonsignificant null pooled correlation (P = 0.85). We observed high heterogeneity in most meta-analyses, and climate zonation was shown to influence the pooled estimates. Linkages between MPA and water quality properties will enhance our capacity to predict MBD risks under changing environmental and land use changes.

Diversity of larval habitats of Anopheles mosquitoes in urban areas of Benin and influence of their physicochemical and bacteriological characteristics on larval density

Background

The implementation of anti-larval strategies in the fight against malaria vectors requires fundamental knowledge of their oviposition sites. The aim of this study was to assess the spatial and temporal distribution of Anopheles breeding sites as well as the influence of abiotic and biotic factors on the proliferation of larvae in urban and non-urban areas of Benin.

Methods

Sampling of Anopheles larvae was carried out during the rainy and dry seasons in urbanized and non-urbanized areas of the cities of Cotonou, Bohicon, Parakou, and Natitingou in Benin. The Anopheles larval breeding sites were georeferenced and characterized by their nature, type, physicochemical (pH, temperature, dissolved oxygen, conductivity, turbidity, salinity) and biological attributes (larval density and coliform density).

Results

A total of 198 positive breeding sites for Anopheles larvae were identified, comprising 163 (82.3%) in the rainy season and 35 (17.7%) in the dry season. Out of these larval habitats, 61.9% were located in urbanized areas, and were predominantly puddles. Principal component analysis revealed a high positive correlation of larval density with temperature and dissolved oxygen, and with salinity in the coastal zone. In addition, cross-sectional analysis of the microbiological results with larval density showed a significant negative correlation between larval productivity and faecal coliform load.

Conclusions

This study indicated the presence of multiple larval habitats of Anopheles in the urban areas which were created through human activities, and associations between larval density and intrinsic factors of the habitats such as temperature, dissolved oxygen and faecal coliform load. This type of information may be useful for the implementation of appropriate control strategies in urban areas, including regulation of the human activities that lead to the creation of breeding sites, proper environmental management and targeted larvicidal use.

Graphical abstract