Malaria-Transmitting Vectors Microbiota: Overview and Interactions With Anopheles Mosquito Biology

Identifying antimalarials that disrupt malaria parasite transmission when fed to the mosquito

A decade-long decline in malaria cases has plateaued, primarily due to parasite drug resistance and mosquito resistance to insecticides used in bed nets and indoor residual spraying. Here, we explore the innovative control strategy targeting Plasmodium with antimalarials during the mosquito stages. This strategy has the potential to reduce the risk of resistance emerging because a relatively small population of parasites within the mosquito is subject to selection. After validating mosquito feeding strategies, we screened a range of parasiticidal compounds by feeding them to mosquitoes already infected with mouse malaria (P. berghei). Three antimalarials showed activity against P. berghei in mosquitoes, apparently targeting specific stages of P. berghei development during transmission. Borrelidin, a threonyl-tRNA synthetase inhibitor, significantly reduced P. berghei sporozoite numbers. Azithromycin, an antibiotic targeting apicoplast protein synthesis, significantly lowered sporozoite infectivity in mice. T111, a next generation compound targeting the parasite electron transport chain, reduced sporozoite numbers in P. berghei at equivalent concentrations to the gold standard electron transport chain inhibitor, atovaquone. T111 also prevented sporozoite production in mosquitoes infected with human malaria, P. falciparum, even after very short exposure times. Encouragingly, T111 remained efficacious after being freeze-dried onto a substrate and later reconstituted with water, suggesting this compound would be effective in easy-to-distribute-and-deploy transmission control devices. Our findings suggest that several antimalarials can be used to target mosquito-stage parasites via sugar baits and limit malaria transmission. Importantly, mosquito feeding of antimalarials could vastly increase the range of potentially useful parasiticidal compounds to include those failing to meet the exacting standards required for human antimalarial drugs, potentially improving malaria control for minimal cost.

A comparison of the structure and diversity of the microbial communities of Culicoides midges

Culicoides midges (Diptera: Ceratopogonidae) comprise over 1400 species globally and are vectors for several human and veterinary pathogens. The microbiota of insect vectors plays an essential role in the interactions between the host and pathogen and can impact the ability of the insect to transmit pathogens or parasites. Characterizing the microbiome composition of Culicoides could yield novel approaches to control midge populations and impact disease transmission. This study characterized and compared the bacterial and fungal microbiota of five Culicoides species. Utilizing 16S and ITS amplicon sequencing, we identified diverse bacterial communities, with Proteobacteria as the most abundant phylum. Notably, Rickettsia, Midichloria, and Asaia were the predominant genera across samples. Fungal analysis revealed Ascomycota as the primary taxon, with Cladosporium being the most prevalent genus. Little difference in overall bacterial and fungal diversity was observed between species, suggesting that the five Culicoides species examined share some common members of their microbiota but differ in overall composition. Our findings highlight the potential of exploiting midge-associated microbiota for developing novel biological control strategies to target Culicoides species populations and the pathogens they transmit.

Targeting the mosquito prefoldin-chaperonin complex blocks Plasmodium transmission

The Plasmodium infection cycle in mosquitoes relies on numerous host factors in the vector midgut, which can be targeted with therapeutics. The mosquito prefoldin complex is needed to fold proteins and macromolecular complexes properly. Here we show that the conserved Anopheles mosquito prefoldin (PFDN)-chaperonin system is a potent transmission-blocking target for multiple Plasmodium species. Silencing any prefoldin subunit or its CCT/TRiC partner via RNA interference reduces Plasmodium falciparum oocyst loads in the mosquito midgut, as does co-feeding mosquitoes with PFDN6-specific antibody and gametocytes. Inhibition of the PFDN-CCT/TRiC chaperonin complex results in the loss of epithelial and extracellular matrix integrity, which triggers microorganism-mediated anti-Plasmodium immune priming and compromises the parasite's laminin-based immune evasion. Mouse malaria transmission-blocking vaccine and antibody co-feeding assays support its potential as a multispecies transmission-blocking target for P. falciparum and Plasmodium vivax. Further study is needed to determine the potential of this system as a transmission-blocking vaccine target.

Towards transforming malaria vector surveillance using VectorBrain: a novel convolutional neural network for mosquito species, sex, and abdomen status identifications

Malaria is a major public health concern, causing significant morbidity and mortality globally. Monitoring the local population density and diversity of the vectors transmitting malaria is critical to implementing targeted control strategies. However, the current manual identification of mosquitoes is a time-consuming and intensive task, posing challenges in low-resource areas like sub-Saharan Africa; in addition, existing automated identification methods lack scalability, mobile deployability, and field-test validity. To address these bottlenecks, a mosquito image database with fresh wild-caught specimens using basic smartphones is introduced, and we present a novel CNN-based architecture, VectorBrain, designed for identifying the species, sex, and abdomen status of a mosquito concurrently while being efficient and lightweight in computation and size. Overall, our proposed approach achieves 94.44±2% accuracy with a macro-averaged F1 score of 94.10±2% for the species classification, 97.66±1% accuracy with a macro-averaged F1 score of 96.17±1% for the sex classification, and 82.20±3.1% accuracy with a macro-averaged F1 score of 81.17±3% for the abdominal status classification. VectorBrain running on local mobile devices, paired with a low-cost handheld imaging tool, is promising in transforming the mosquito vector surveillance programs by reducing the burden of expertise required and facilitating timely response based on accurate monitoring.

Malaria reporting timeliness analysis and factors associated with delayed notification, 2018-2022, Nepal

In order to monitor public health trends and identify disease outbreaks early, efficient and reliable notification and surveillance systems are essential. Nepal uses a 1-3-7 malaria surveillance approach. The Short Message System (SMS) -based system for timely notification has been established. However, knowledge gaps exist regarding the timeliness of notification, treatment initiation, and case-based investigations. Hence, this study identifies the timeliness of notification and factors associated with delayed notification. This study used a cross-sectional approach and used secondary malaria surveillance data from Nepal's national malaria elimination program for the period of 2018 to 2022. The study revealed that the majority (79.9%) of malaria cases were male, with a male-to-female ratio of 3.96:1. Occupation was found to be significantly associated with delayed notification. Repatriate workers had 0.60 times lower odds of experiencing delayed notification compared to the reference occupation. Similarly, individuals diagnosed in the Sudurpaschim and Lumbini provinces had significantly lower odds (0.48 and 0.38, respectively) of encountering delayed notification compared to the reference province. Furthermore, relying on a single laboratory tool for malaria diagnosis (either RDT or microscopy only) was significantly associated with delayed notification. Individuals diagnosed solely with RDT or microscopy had 2.04 and 1.79 times higher odds of experiencing delayed notification, respectively, compared to those diagnosed using both laboratory tools. This study provides insight into the timeliness of surveillance system approach by assessing delayed notification and the factors associated with it. No delays are identified in median notification, treatment time and in case investigation. Improvement in the timeliness of malaria reporting over the years was observed. Provinces with high burden of malaria and repatriate workers showed lower delayed notification and conversely, cases diagnosed with single laboratory tool showed delayed notification time.

Mosquito Gut Microbiota: A Review

Mosquitoes are vectors of many important human diseases. The prolonged and widespread use of insecticides has led to the development of mosquito resistance to these insecticides. The gut microbiota is considered the master of host development and physiology; it influences mosquito biology, disease pathogen transmission, and resistance to insecticides. Understanding the role and mechanisms of mosquito gut microbiota in mosquito insecticide resistance is useful for developing new strategies for tackling mosquito insecticide resistance. We searched online databases, including PubMed, MEDLINE, SciELO, Web of Science, and the Chinese Science Citation Database. We searched all terms, including microbiota and mosquitoes, or any specific genera or species of mosquitoes. We reviewed the relationships between microbiota and mosquito growth, development, survival, reproduction, and disease pathogen transmission, as well as the interactions between microbiota and mosquito insecticide resistance. Overall, 429 studies were included in this review after filtering 8139 search results. Mosquito gut microbiota show a complex community structure with rich species diversity, dynamic changes in the species composition over time (season) and across space (environmental setting), and variation among mosquito species and mosquito developmental stages (larval vs. adult). The community composition of the microbiota plays profound roles in mosquito development, survival, and reproduction. There was a reciprocal interaction between the mosquito midgut microbiota and virus infection in mosquitoes. Wolbachia, Asaia, and Serratia are the three most studied bacteria that influence disease pathogen transmission. The insecticide resistance or exposure led to the enrichment or reduction in certain microorganisms in the resistant mosquitoes while enhancing the abundance of other microorganisms in insect-susceptible mosquitoes, and they involved many different species/genera/families of microorganisms. Conversely, microbiota can promote insecticide resistance in their hosts by isolating and degrading insecticidal compounds or altering the expression of host genes and metabolic detoxification enzymes. Currently, knowledge is scarce about the community structure of mosquito gut microbiota and its functionality in relation to mosquito pathogen transmission and insecticide resistance. The new multi-omics techniques should be adopted to find the links among environment, mosquito, and host and bring mosquito microbiota studies to the next level.

The Impact of Environmental Gaseous Pollutants on the Cultivable Bacterial and Fungal Communities of the Aerobiome

Understanding air microbial content, especially in highly polluted urban areas, is crucial for assessing its effect on human health and ecosystems. In this context, the impact of gaseous pollutants on the aerobiome remains inconclusive due to a lack of studies separating this factor from other contaminants or environmental factors. In this study, we aimed to experimentally assess the influence of contrasting concentrations of atmospheric gaseous pollutants as isolated variables on the composition of the aerobiome. Our study sites were contrasting Air Quality Index (AQI) sites of the Metropolitan Region of Chile, where nitric oxide (NO) was significantly lower at the low-AQI site than at the high-AQI site, while ozone (O3) was significantly higher. Cultivable aerobiome communities from the low-AQI site were exposed to their own pollutants or those from the high-AQI site and characterized using high-throughput sequencing (HTS), which allowed comparisons between the entire cultivable communities. The results showed increased alpha diversity in bacterial and fungal communities exposed to the high-AQI site compared to the low-AQI site. Beta diversity and compositional hierarchical clustering analyses revealed a clear separation based on NO and O3 concentrations. At the phylum level, four bacterial and three fungal phyla were identified, revealing an over-representation of Actinobacteriota and Basidiomycota in the samples transferred to the high-AQI site, while Proteobacteria were more abundant in the community maintained at the low-AQI site. At the functional level, bacterial imputed functions were over-represented only in samples maintained at the low-AQI site, while fungal functions were affected in both conditions. Overall, our results highlight the impact of NO and/or O3 on both taxonomic and functional compositions of the cultivable aerobiome. This study provides, for the first time, insights into the influence of contrasting pollutant gases on entire bacterial and fungal cultivable communities through a controlled environmental intervention.

Structure-based virtual screening study for identification of potent insecticides against Anopheles gambiae to combat the malaria

BACKGROUND OBJECTIVES

Vector-borne infectious diseases contribute significantly to global mortality, with over 700,000 annual deaths, and malaria alone accounts for more than 400,000 of these fatalities. Anopheles gambiae, a prominent mosquito species, serves as a primary vector for transmitting malaria to humans. To address this issue, researchers have identified the D1-like dopamine receptor (DAR), specifically DOP2, as a promising target for developing new insecticides.

METHODS

The three-dimensional structure of DOP2 from A. gambiae was unavailable; in-silico approach was used to model and validate DOP2 structure. The Discovery Studio 2021 program was used to identify potential binding sites on DOP2. Virtual screening of 235 anti-parasitic compounds was performed against DOP2 using PyRx 0.8.

RESULTS

The screening demonstrated strong binding and interactions with active site residues of DOP2 for five compounds: Diclazuril, Kaempferol, Deracoxib, Clindamycin, and Diaveridine. These compounds exhibited higher binding affinity values compared to the control (Asenapine). In addition, the predicted physiochemical properties for these compounds were within acceptable ranges and there were no violations in drug-likeness properties.

INTERPRETATION CONCLUSION

These compounds show promise as potential new insecticides targeting A. gambiae mosquito by inhibiting the DOP2 protein. However, additional experimental validation is required to optimize their efficacy as DOP2 inhibitors.

Vectorial competence, insecticide resistance in Anopheles funestus and operational implications for malaria vector control strategies in Benin Republic

The primary reason for the failure of malaria vector control across endemic regions is the widespread insecticide resistance observed in Anopheles vectors. The most dominant African vectors of malaria parasites are Anopheles gambiae and Anopheles funestus mosquitoes. These species often exhibit divergent behaviours and adaptive changes underscoring the importance of deploying active and effective measures in their control. Unlike An. gambiae, An. funestus mosquitoes are poorly studied in Benin Republic. However, recent reports indicated that An. funestus can adapt and colonize various ecological niches owing to its resistance against insecticides and adaptation to changing breeding habitats. Unfortunately, scientific investigations on the contribution of An. funestus to malaria transmission, their susceptibility to insecticide and resistance mechanism developed are currently insufficient for the design of better control strategies. In an attempt to gather valuable information on An. funestus, the present review examines the progress made on this malaria vector species in Benin Republic and highlights future research perspectives on insecticide resistance profiles and related mechanisms, as well as new potential control strategies against An. funestus. Literature analysis revealed that An. funestus is distributed all over the country, although present in low density compared to other dominant malaria vectors. Interestingly, An. funestus is being found in abundance during the dry seasons, suggesting an adaptation to desiccation. Among the An. funestus group, only An. funestus sensu stricto (s.s.) and Anopheles leesoni were found in the country with An. funestus s.s. being the most abundant species. Furthermore, An. funestus s.s. is the only one species in the group contributing to malaria transmission and have adapted biting times that allow them to bite at dawn. In addition, across the country, An. funestus were found resistant to pyrethroid insecticides used for bed nets impregnation and also resistant to bendiocarb which is currently being introduced in indoor residual spraying formulation in malaria endemic regions. All these findings highlight the challenges faced in controlling this malaria vector. Therefore, advancing the knowledge of vectorial competence of An. funestus, understanding the dynamics of insecticide resistance in this malaria vector, and exploring alternative vector control measures, are critical for sustainable malaria control efforts in Benin Republic.

Holobiont perspectives on tripartite interactions among microbiota, mosquitoes, and pathogens

Mosquito-borne diseases like dengue and malaria cause a significant global health burden. Unfortunately, current insecticides and environmental control strategies aimed at the vectors of these diseases are only moderately effective in decreasing disease burden. Understanding and manipulating the interaction between the mosquito holobiont (i.e., mosquitoes and their resident microbiota) and the pathogens transmitted by these mosquitoes to humans and animals could help in developing new disease control strategies. Different microorganisms found in the mosquito's microbiota affect traits related to mosquito survival, development, and reproduction. Here, we review the physiological effects of essential microbes on their mosquito hosts; the interactions between the mosquito holobiont and mosquito-borne pathogen (MBP) infections, including microbiota-induced host immune activation and Wolbachia-mediated pathogen blocking (PB); and the effects of environmental factors and host regulation on the composition of the microbiota. Finally, we briefly overview future directions in holobiont studies, and how these may lead to new effective control strategies against mosquitoes and their transmitted diseases.

Bacterial Microbiota from Lab-Reared and Field-Captured Anopheles darlingi Midgut and Salivary Gland

Anopheles darlingi is a major malaria vector in the Amazon region and, like other vectors, harbors a community of microorganisms with which it shares a network of interactions. Here, we describe the diversity and bacterial composition from the midguts and salivary glands of lab-reared and field-captured An. darlingi using metagenome sequencing of the 16S rRNA gene. The libraries were built using the amplification of the region V3-V4 16S rRNA gene. The bacterial community from the salivary glands was more diverse and richer than the community from the midguts. However, the salivary glands and midguts only showed dissimilarities in beta diversity between lab-reared mosquitoes. Despite that, intra-variability was observed in the samples. Acinetobacter and Pseudomonas were dominant in the tissues of lab-reared mosquitoes. Sequences of Wolbachia and Asaia were both found in the tissue of lab-reared mosquitoes; however, only Asaia was found in field-captured An. darlingi, but in low abundance. This is the first report on the characterization of microbiota composition from the salivary glands of An. darlingi from lab-reared and field-captured individuals. This study can provide invaluable insights for future investigations regarding mosquito development and interaction between mosquito microbiota and Plasmodium sp.