Mapping the breeding sites of Anopheles gambiae s. l. in areas of residual malaria transmission in central western Senegal

Community participatory mapping of malaria mosquito breeding sites in Mozambique

BACKGROUND

The community involvement and the people's knowledge allow detailed information about the distribution, location, and identification of mosquito breeding-sites. Information which is fundamental for their efficient management and elimination. Since participatory mapping has proven to be an effective tool to identify health determinants, the study aimed to apply the methodology to identify and map potential mosquito breeding-sites in Tambai, Nhamatanda, Mozambique.

METHODS

A study was conducted using an open-question guide. Discussions were held with 94 participants within ten focus groups, selected in collaboration with local community leaders. A thematic content analysis was performed. Descriptive statistics were used to characterize sociodemographic data. Geographic Positioning System (GPS) was used to compare and map potential breeding-sites. Children under 5 years of age who tested positive for malaria, were georeferenced to the maps.

RESULTS

Participants were aware of causes and transmission of malaria, no major differences between groups were observed regarding knowledge and identification of principal potential breeding sites. Gender and age determined specific information, number, and diversity of identified potential breeding sites. A total of 125 potential breeding-sites (36 permanent and 89 temporary) were mapped.

CONCLUSIONS

Several potential mosquito breeding-sites were identified, located throughout the community, often near house conglomerates and malaria cases. Community participatory mapping could be used to identify potential mosquito breeding-sites by the national malaria control programmes to establish an efficient larval surveillance system, while improving community engagement and control strategies.

TRIAL REGISTRATION

ClinicalTrials.gov ID: NCT04419766.

Assessment of environmental and spatial factors influencing the establishment of Anopheles gambiae larval habitats in the malaria endemic province of Woleu-Ntem, northern Gabon

BACKGROUND

This study aimed to assess the spatial distribution of Anopheles mosquito larval habitats and the environmental factors associated with them, as a prerequisite for the implementation of larviciding.

METHODS

The study was conducted in December 2021, during the transition period between the end of the short rainy season (September-November) and the short dry season (December-February). Physical, biological, and land cover data were integrated with entomological observations to collect Anopheles larvae in three major towns: Mitzic, Oyem, and Bitam, using the "dipping" method during the transition from rainy to dry season. The collected larvae were then reared in a field laboratory established for the study period. After the Anopheles mosquitoes had emerged, their species were identified using appropriate morphological taxonomic keys. To determine the influence of environmental factors on the breeding of Anopheles mosquitoes, multiple-factor analysis (MFA) and a binomial generalized linear model were used.

RESULTS

According to the study, only 33.1% out of the 284 larval habitats examined were found to be positive for Anopheles larvae, which were primarily identified as belonging to the Anopheles gambiae complex. The findings of the research suggested that the presence of An. gambiae complex larvae in larval habitats was associated with various significant factors such as higher urbanization, the size and type of the larval habitats (pools and puddles), co-occurrence with Culex and Aedes larvae, hot spots in ambient temperature, moderate rainfall, and land use patterns.

CONCLUSIONS

The results of this research mark the initiation of a focused vector control plan that aims to eradicate or lessen the larval habitats of An. gambiae mosquitoes in Gabon's Woleu Ntem province. This approach deals with the root causes of malaria transmission through larvae and is consistent with the World Health Organization's (WHO) worldwide objective to decrease malaria prevalence in regions where it is endemic.

Updates on traditional methods for combating malaria and emerging Wolbachia-based interventions

The escalating challenge of malaria control necessitates innovative approaches that extend beyond traditional control strategies. This review explores the incorporation of traditional vector control techniques with emerging Wolbachia-based interventions. Wolbachia, a naturally occurring bacteria, offers a novel approach for combatting vector-borne diseases, including malaria, by reducing the mosquitoes' ability to transmit these diseases. The study explores the rationale for this integration, presenting various case studies and pilot projects that have exhibited significant success. Employing a multi-dimensional approach that includes community mobilization, environmental modifications, and new biological methods, the paper posits that integrated efforts could mark a turning point in the struggle against malaria. Our findings indicate that incorporating Wolbachia-based strategies into existing vector management programs not only is feasible but also heightens the efficacy of malaria control initiatives in different countries especially in Pakistan. The paper concludes that continued research and international collaboration are imperative for translating these promising methods from the laboratory to the field, thereby offering a more sustainable and effective malaria control strategy.

Profiles of bacterial communities and environmental factors associated with proliferation of malaria vector mosquitoes within the Kenyan Coast

Background

Since Anopheles mosquitoes which transmit and maintain the malaria parasite breed in the outdoor environment, there is an urgent need to manage these mosquito breeding sites. In order to elaborate more on the ecological landscape of mosquito breeding sites, the bacterial community structure and their interactions with physicochemical factors in mosquito larval habitats was characterised in Kwale County (Kenya), where malaria is endemic.

Methods

The physical characteristics and water physicochemical parameters of the habitats were determined and recorded. Water samples were also collected from the identified sites for total metagenomic DNA extraction in order to characterise the bacterial communities within the breeding sites.

Results and Discussion

Sites where mosquito larvae were found were described as positive and those without mosquito larvae as negative. Electrical conductivity, total dissolved solids, salinity and ammonia were lower in the rainy season than in the dry season, which also coincided with a high proportion of positive sites. Pseudomonadota was the most common phyla recovered in all samples followed by Bacteroidota and then Actinomycetota. The presence or absence of mosquito larvae in a potential proliferation site was not related to the bacterial community structure in the sampled sites, but was positively correlated with bacterial richness and evenness.

Conclusion

Generally, the presence of Anopheles mosquito larvae was found to be positively correlated with rainy season, bacterial richness and evenness, and negatively correlated with electrical conductivity, total dissolved solids, salinity and ammonia. The findings of this study have implications for predicting the potential of environmental water samples to become mosquito proliferation sites.

Mapping Malaria Vector Habitats in West Africa: Drone Imagery and Deep Learning Analysis for Targeted Vector Surveillance

Disease control programs are needed to identify the breeding sites of mosquitoes, which transmit malaria and other diseases, in order to target interventions and identify environmental risk factors. The increasing availability of very-high-resolution drone data provides new opportunities to find and characterize these vector breeding sites. Within this study, drone images from two malaria-endemic regions in Burkina Faso and Côte d'Ivoire were assembled and labeled using open-source tools. We developed and applied a workflow using region-of-interest-based and deep learning methods to identify land cover types associated with vector breeding sites from very-high-resolution natural color imagery. Analysis methods were assessed using cross-validation and achieved maximum Dice coefficients of 0.68 and 0.75 for vegetated and non-vegetated water bodies, respectively. This classifier consistently identified the presence of other land cover types associated with the breeding sites, obtaining Dice coefficients of 0.88 for tillage and crops, 0.87 for buildings and 0.71 for roads. This study establishes a framework for developing deep learning approaches to identify vector breeding sites and highlights the need to evaluate how results will be used by control programs.

Residual malaria transmission and the role of Anopheles arabiensis and Anopheles melas in central Senegal

Understanding the behavior and ecology of local malaria vectors is essential for the effectiveness of the commonly used vector-targeted malaria control tools in areas of low malaria transmission. This study was conducted to determine species composition, biting behavior and infectivity of the major Anopheles vectors of Plasmodium falciparum in low transmission settings in central Senegal. Adult mosquitoes were collected using human landing catches during 2 consecutive nights and Pyrethrum Spray Catches in 30-40 randomly selected rooms, from July 2017 to December 2018 in 3 villages. Anopheline mosquitoes were morphologically identified using conventional keys; their reproductive status assessed by ovary dissections, and a sub-sample of Anopheles gambiae s.l. were identified to species level using polymerase chain reaction (PCR). Plasmodium sporozoite infections were detected using real-time quantitative PCR. During this study 3684 Anopheles were collected of which 97% were An. gambiae s.l., 0.6% were Anopheles funestus, and 2.4% were Anopheles pharoensis. Molecular identification of 1,877 An. gambiae s.l. revealed a predominance of Anopheles arabiensis (68.7%), followed by Anopheles melas (28.8%), and Anopheles coluzzii (2.1%). The overall human-biting rate of An. gambiae s.l. was highest in the inland site of Keur Martin with 4.92 bites per person per night, while it was similar in the deltaic site, Diofior (0.51) and the coastal site, Mbine Coly (0.67). Parity rates were similar in An. arabiensis (45%) and An. melas (42%). Sporozoite infections were detected in both An. arabiensis and An. melas with the respective infection rates of 1.39% (N = 8) and 0.41% (N = 1). Results suggest that low residual malaria in central Senegal is transmitted by An. arabiensis and An. melas. Consequently, both vectors will need to be targeted as part of malaria elimination efforts in this area of Senegal.

Fine-scale mapping of urban malaria exposure under data scarcity: an approach centred on vector ecology

BACKGROUND

Although malaria transmission has experienced an overall decline in sub-Saharan Africa, urban malaria is now considered an emerging health issue due to rapid and uncontrolled urbanization and the adaptation of vectors to urban environments. Fine-scale hazard and exposure maps are required to support evidence-based policies and targeted interventions, but data-driven predictive spatial modelling is hindered by gaps in epidemiological and entomological data. A knowledge-based geospatial framework is proposed for mapping the heterogeneity of urban malaria hazard and exposure under data scarcity. It builds on proven geospatial methods, implements open-source algorithms, and relies heavily on vector ecology knowledge and the involvement of local experts.

METHODS

A workflow for producing fine-scale maps was systematized, and most processing steps were automated. The method was evaluated through its application to the metropolitan area of Dakar, Senegal, where urban transmission has long been confirmed. Urban malaria exposure was defined as the contact risk between adult Anopheles vectors (the hazard) and urban population and accounted for socioeconomic vulnerability by including the dimension of urban deprivation that is reflected in the morphology of the built-up fabric. Larval habitat suitability was mapped through a deductive geospatial approach involving the participation of experts with a strong background in vector ecology and validated with existing geolocated entomological data. Adult vector habitat suitability was derived through a similar process, based on dispersal from suitable breeding site locations. The resulting hazard map was combined with a population density map to generate a gridded urban malaria exposure map at a spatial resolution of 100 m.

RESULTS

The identification of key criteria influencing vector habitat suitability, their translation into geospatial layers, and the assessment of their relative importance are major outcomes of the study that can serve as a basis for replication in other sub-Saharan African cities. Quantitative validation of the larval habitat suitability map demonstrates the reliable performance of the deductive approach, and the added value of including local vector ecology experts in the process. The patterns displayed in the hazard and exposure maps reflect the high degree of heterogeneity that exists throughout the city of Dakar and its suburbs, due not only to the influence of environmental factors, but also to urban deprivation.

CONCLUSIONS

This study is an effort to bring geospatial research output closer to effective support tools for local stakeholders and decision makers. Its major contributions are the identification of a broad set of criteria related to vector ecology and the systematization of the workflow for producing fine-scale maps. In a context of epidemiological and entomological data scarcity, vector ecology knowledge is key for mapping urban malaria exposure. An application of the framework to Dakar showed its potential in this regard. Fine-grained heterogeneity was revealed by the output maps, and besides the influence of environmental factors, the strong links between urban malaria and deprivation were also highlighted.

Towards environmental detection, quantification, and molecular characterization of Anopheles stephensi and Aedes aegypti from experimental larval breeding sites

The invasion and establishment of An. stephensi mosquitoes in the Horn of Africa represents a significant regional threat, which may jeopardise malaria control, particularly in urban areas which were formally free from disease transmission. Novel vector surveillance methods are urgently needed, both agnostic to mosquito larval morphology, and simple to implement at the sampling stage. Using new multiplex TaqMan assays, specifically targeting An. stephensi and Ae. aegypti, we validated the use of environmental DNA (eDNA) for simultaneous vector detection in shared artificial breeding sites. Study findings demonstrated that An. stephensi and Ae. aegypti eDNA deposited by as few as one second instar larva in 1L of water was detectable. Characterization of molecular insecticide resistance mechanisms, using novel amplicon-sequencing panels for both vector species, was possible from eDNA shed by as few as 16-32 s instar larvae in 50 ml of water. An. stephensi eDNA, derived from emergent pupae for 24 h, was remarkably stable, and still detectable ~ 2 weeks later. eDNA surveillance has the potential to be implemented in local endemic communities and at points of country entry, to monitor the spread of invasive vector species. Further studies are required to validate the feasibility of this technique under field conditions.

Spatial modelling of malaria prevalence associated with geographical factors in Houet province of Burkina Faso, West Africa

Malaria is a permanent threat to health in western Burkina Faso. Research has shown that geographical variables contribute to the spatial distribution in its transmission. The objective of this study is to assess the relationship between malaria prevalence and potential explanatory geographical variables in the Houet province in Burkina Faso. Statistics on malaria prevalence registered by health centres in the Houet province in 2017 and potential geographical variables identified through a literature review were collected. An Ordinary Least Squares (OLS) regression was used to identify key geographical variables and to measure their association with malaria while the Getis Ord Gi* index was used to locate malaria hotspots. The results showed that average annual temperature, vegetation density, percentage of clay in the soil, total annual rainfall and distance to the nearest waterbody are the main variables associated with malaria prevalence. These variables account for two-thirds of the spatial variability of malaria prevalence observed in Houet province. The intensity and direction of the relationship between malaria prevalence and geographical factors vary according to the variable. Hence, only vegetation density is positively correlated with malaria prevalence. Average temperature, for soil clay content, annual rainfall and for distance to the nearest water body are negatively correlated with the disease prevalence. These results show that even in an endemic area, malaria prevalence has significant spatial variation. The results could contribute to the choice of intervention sites, as this choice is crucial for reducing the malaria burden.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10708-022-10692-7.

Characterization of an outbreak of malaria in a non-endemic zone on the coastal region of Ecuador

Introduction:

Malar¡a ¡s a vector-borne d¡sease w¡dely d¡str¡buted ¡n the Amazon reg¡on and the coastal area of northern Ecuador. Its ep¡dem¡ology ¡nvolves related factors such as human settlements, vector reproduct¡on s¡tes, mob¡l¡ty, product¡ve act¡v¡ty, and the response capac¡ty of health systems, among others.

Objective:

To describe malaria transm¡ss¡on by Plasmodium vivax ¡n a non-endem¡c area of Ecuador by analyz¡ng the ep¡dem¡olog¡cal and entomolog¡cal factors ¡nvolved.

Materials and methods:

We conducted the epidemiological study of the cases reported ¡n the Sal¡nas canton and the character¡zat¡on of vector breed¡ng s¡tes through captures of larvae and adult mosqu¡toes by human capture of rest¡ng mosqu¡toes.

Results:

We detected 21 cases of malar¡a w¡th local transm¡ss¡on related to the presence of ¡n¡t¡al cases ¡n Venezuelan rrrigrant pat¡ents and ¡dentified Anopheles albimanus as the predom¡nant vector ¡n natural breed¡ng s¡tes such as estuar¡es, wells, and water channels.

Conclusions:

We detected an outbreak of malar¡a tr¡ggered by ¡mported cases from Venezuela. Cl¡mat¡c, soc¡al, env¡ronmental, and ecolog¡cal cond¡t¡ons have favored the development of the vector maintaining the transm¡ss¡on cycle. Strateg¡es to control ¡mported malar¡a should be mult¡ple ¡nclud¡ng early case detect¡on and control of product¡ve breed¡ng s¡tes to avo¡d local transm¡ss¡on.