Biological Control of Mosquito-Borne Diseases: The Potential of Wolbachia-Based Interventions in an IVM Framework

Molecular identification and GC-MS analysis of a newly isolated novel bacterium (Lysinibacillus sp. VCRC B655) for mosquito control

BACKGROUND

Mosquitoes are widespread globally and have contributed to transmitting pathogens to humans and the burden of vector-borne diseases. They are effectively controlled at their larval stages by biocontrol agents. Unravelling natural sources for microbial agents can lead us to novel potential candidates for managing mosquito-borne diseases. In the present study, an attempt was made to isolate a novel bacterium from the field-collected agricultural soil for larvicidal activity and promising bacterial metabolites for human healthcare.

METHODS AND RESULTS

Field-collected soil samples from the Union territory of Puducherry, India, have been used as the source of bacteria. Isolate VCRC B655 belonging to the genus Lysinibacillus was identified by 16S rRNA gene sequencing and exhibited promising larvicidal activity against different mosquito species, including Culex (Cx.) quinquefasciatus, Anopheles (An.) stephensi, and Aedes (Ae.) aegypti. The lethal concentration (LC) of Lysinibacillus sp. VCRCB655 was observed to be high for Cx. quiquefasciatus: LC50 at 0.047 mg/l, LC90 at 0.086 mg/l, followed by An. stephensi and Ae. aegypti (LC50: 0.6952 mg/l and 0.795 mg/l) respectively. Additionally, metabolic profiling of the culture supernatant was carried out through Gas chromatography and Mass spectrophotometry (GC/MS) and identified 15 major secondary metabolites of different metabolic classes. Diketopiperazine (DKPs), notably pyro lo [1, 2-a] pyrazine1, 4-dione, are the abundant compounds reported for antioxidant activity, and an insecticide compound benzeneacetic acid was also identified.

CONCLUSIONS

A new bacterial isolate, Lysinibacillus sp. VCRC B655 has been identified with significant larvicidal activity against mosquito larvae with no observed in non-target organisms. GC-MS analysis revealed diverse bioactive compounds with substantial biological applications. In conclusion, Lysinibacillus sp. VCRC B655 showed promise as an alternative biocontrol agent for mosquito vector control, with additional biological applications further enhancing its significance.

Post-Translational Modifications of Proteins of Malaria Parasites during the Life Cycle

Post-translational modifications (PTMs) are essential for regulating protein functions, influencing various fundamental processes in eukaryotes. These include, but are not limited to, cell signaling, protein trafficking, the epigenetic control of gene expression, and control of the cell cycle, as well as cell proliferation, differentiation, and interactions between cells. In this review, we discuss protein PTMs that play a key role in the malaria parasite biology and its pathogenesis. Phosphorylation, acetylation, methylation, lipidation and lipoxidation, glycosylation, ubiquitination and sumoylation, nitrosylation and glutathionylation, all of which occur in malarial parasites, are reviewed. We provide information regarding the biological significance of these modifications along all phases of the complex life cycle of Plasmodium spp. Importantly, not only the parasite, but also the host and vector protein PTMs are often crucial for parasite growth and development. In addition to metabolic regulations, protein PTMs can result in epitopes that are able to elicit both innate and adaptive immune responses of the host or vector. We discuss some existing and prospective results from antimalarial drug discovery trials that target various PTM-related processes in the parasite or host.

In vitro maintenance of the endosymbiont Wolbachia of Dirofilaria immitis

Wolbachia has an obligatory mutualistic relationship with many onchocercid nematodes of the subfamilies Dirofilariinae and Onchocercinae. Till date, no attempts have been made for the in vitro cultivation of this intracellular bacterium from the filarioid host. Hence, the current study attempted cell co-culture method using embryonic Drosophila S2 and the LD cell lines to cultivate Wolbachia from Dirofilaria immitis microfilariae (mfs) harvested from infected dogs. Microfilariae (mfs = 1500) were inoculated in shell vials supplemented with Schneider medium using both cell lines. The establishment and multiplication of the bacterium were observed during the initial inoculation, at day 0 and before every medium change (from days 14 to 115). An aliquot (50 µl) from each time point was tested by quantitative real-time PCR (qPCR). Comparing the average of Ct values, obtained by the tested parameters (i.e., LD/S2 cell lines and mfs with/without treatment), the S2 cell line without mechanical disruption of mfs provided the highest Wolbachia cell count by qPCR. Despite the maintenance of Wolbachia within both S2 and LD-based cell co-culture models for up to 115 days, a definitive conclusion is still far. Further trials using fluorescent microscopy and viable staining will help to demonstrate the cell line infection and viability of Wolbachia. Use of considerable amount of untreated mfs to inoculate the Drosophilia S2 cell lines, as well as the supplementation of the culture media with growth stimulants or pre-treated cells to increase their susceptibility for the infection and development of a filarioid-based cell line system are recommended for the future trials.

Mosquito-Borne Diseases and Their Control Strategies: An Overview Focused on Green Synthesized Plant-Based Metallic Nanoparticles

Mosquitoes act as vectors of pathogens that cause most life-threatening diseases, such as malaria, Dengue, Chikungunya, Yellow fever, Zika, West Nile, Lymphatic filariasis, etc. To reduce the transmission of these mosquito-borne diseases in humans, several chemical, biological, mechanical, and pharmaceutical methods of control are used. However, these different strategies are facing important and timely challenges that include the rapid spread of highly invasive mosquitoes worldwide, the development of resistance in several mosquito species, and the recent outbreaks of novel arthropod-borne viruses (e.g., Dengue, Rift Valley fever, tick-borne encephalitis, West Nile, yellow fever, etc.). Therefore, the development of novel and effective methods of control is urgently needed to manage mosquito vectors. Adapting the principles of nanobiotechnology to mosquito vector control is one of the current approaches. As a single-step, eco-friendly, and biodegradable method that does not require the use of toxic chemicals, the green synthesis of nanoparticles using active toxic agents from plant extracts available since ancient times exhibits antagonistic responses and broad-spectrum target-specific activities against different species of vector mosquitoes. In this article, the current state of knowledge on the different mosquito control strategies in general, and on repellent and mosquitocidal plant-mediated synthesis of nanoparticles in particular, has been reviewed. By doing so, this review may open new doors for research on mosquito-borne diseases.

Identifying the Gut Virome of Diaphorina citri from Florida Groves

Asian citrus psyllid (Diaphorina citri) transmits the bacterial pathogen Candidatus Liberibacter asiaticus (CLas), the putative causative agent of citrus Huanglongbing disease (HLB). Insect-specific viruses can act against insects as their natural enemies, and recently, several D. citri-associated viruses were discovered. The insect gut plays an important role as not only a pool for diverse microbes but also as a physical barrier to prevent the spread of pathogens such as CLas. However, there is little evidence of the presence of D. citri-associated viruses in the gut and of the interaction between them and CLas. Here, we dissected psyllid guts collected from five growing regions in Florida, and the gut virome was analyzed by high throughput sequencing. Four insect viruses, including D. citri-associated C virus (DcACV), D. citri densovirus (DcDV), D. citri reovirus (DcRV), and D. citri flavi-like virus (DcFLV), were identified, and their presence in the gut, including an additional D. citri cimodo-like virus (DcCLV), were confirmed with PCR-based assays. Microscopic analysis showed that DcFLV infection leads to morphological abnormalities in the nuclear structure in the infected psyllid gut cells. The complex and diverse composition of microbiota in the psyllid gut suggests a possible interaction and dynamics between CLas and the D. citri-associated viruses. Our study identified various D. citri-associated viruses that localized in the psyllid gut and provided more information that helps to evaluate the potential vectors for manipulating CLas in the psyllid gut.

Potent Bioactivity of Endophytic Fungi Isolated from Moringa oleifera Leaves

Plant species are known to harbor large number of endophytes, which stays in plant tissues as symbionts. These endophytes secrete large array of bioactive compounds that have potency against certain diseases with no side effects. We have collected leaf samples of the Moringa oleifera plant from the Pakistan Forest Institute, Khyber Pakhtunkhwa, Pakistan for the isolation of beneficial endophytes. The strains isolated from the leaves of M. oleifera were coded with MOL and tested for antimicrobial, antifungal, germicidal, phytotoxic, insecticidal, cytotoxic, and anti-inflammatory activities. The isolates, MOL1, MOL16, MOL19, and MOL21, possessed antibacterial activity against Staphylococcus aureus, whereas MOL7 inhibited 55% of the growth of Escherichia coli. MOL3 inhibited the growth of E. coli, S. aureus, and Pseudomonas aeruginosa. The strains, MOL1 and MOL7, showed antifungal activity against Candida albicans and Saccharomyces cerevisiae, while the strains, MOL11 and MOL17, showed activity against Verticillium chlamydosporium. The isolates, MOL3, MOL7, MOL9, MOL15, MOL17, MOL18, and MOL19, inhibited the growth of Lemna minor (duckweed) at 100 μg/ml. MOL2 exhibited strong activity in the brine shrimp assay, while MOL1, MOL2, MOL5, MOL6, MOL12, MOL17, MOL19, and MOL20 showed insecticidal, and MOL3 demonstrated larvicidal and antileishmanial activity. The isolated potent endophytes were identified as Aspergillus, Penicillium, Fusarium, Tricoderma, Rhizoctonia, Mucor, Alternaria, Pestalotiopsis, Acremonium, and Cladosporium through morphological and microscopic characteristics of the colonies.

Molecular insights on ar-turmerone as a structural, functional and pharmacophoric analogue of synthetic mosquito repellent DEET by comprehensive computational assessment

Mosquitoes are vectors for a variety of infectious illnesses, and chemical synthetic insecticides have made it possible to control them effectively. Mosquito repellents are a typical means of keeping mosquitos at bay. Because of its main effectiveness of skin permeability, N,N-Diethyl-meta-toluamide (DEET) is one of the most extensively used mosquito repellents but a dangerous synthetic chemical. DEET was identified about a decade ago to inhibit mosquito's Odorant Binding Protein 1 (OBP1), impairing the mosquito's ability to recognise the host body odour. OBP1 has been identified as a possible target for the development of new mosquito repellents since its discovery. Essential oils from different plants, on the other hand, have been used to repel mosquitos since antiquity. One essential oil from the Curcuma longa (Zingiberales: Zingiberaceae) rhizome display mosquito repellent properties, according to the literature. Furthermore, one of the phytochemicals found in abundance in C. longa essential oil, ar-turmerone, exhibits mosquito repellency as comparable to synthetic DEET. Till date studies on in-silico interaction of natural ar-turmerone with OBP1, which we depict in our current work are scarce. Further, there exist no published reports demonstrating the literary evidence on detailed insights of interaction of DEET with OBP1 along with Molecular Dynamics (MD) simulation studies. We further performed detailed molecular investigations using pharmacophore analysis of ar-turmerone and compared it with DEET, where our findings in the current manuscript unveils for the first time that ar-turmerone is a functional, structural and pharmacophoric analogue of DEET.

Seasonal Variation of Midgut Bacterial Diversity in Culex quinquefasciatus Populations in Haikou City, Hainan Province, China

Simple Summary

Mosquito midgut microbiota has become an interesting field in mosquito vector biology, as it has been shown to form an integral part of the mosquito life history. But less is known about seasonal variation of midgut bacterial diversity of Culex quinquefasciatus. Our results illustrate that the Bacteroidetes (Bacterial Phyla) communities have been well observed in autumn and winter seasons, suggesting that this might participate in the nutritional supply of adult mosquitoes when temperatures drop. This discovery provides a new perspective for the control of Cx. quinquefasciatus to reduce the transmission of diseases. There is much sufficiently practical significance to reduce the density of Cx. quinquefasciatus in autumn and winter when their activities are weakened, which is of absolute benefit to human beings and the natural environment.

Abstract

Culex quinquefasciatus, one of the most significant mosquito vectors in the world, is widespread in most parts of southern China. A variety of diseases including Bancroft’s filariasis, West Nile disease, and St. Louis encephalitis could be transmitted by the vector. Mosquitoes have been shown to host diverse bacterial communities that vary depending on environmental factors such as temperature and rainfall. In this work, 16S rDNA sequencing was used to analyze the seasonal variation of midgut bacterial diversity of Cx. Quinquefasciatus in Haikou City, Hainan Province, China. Proteobacteria was the dominant phylum, accounting for 79.7% (autumn), 73% (winter), 80.4% (spring), and 84.5% (summer). The abundance of Bacteroidetes in autumn and winter was higher than in others. Interestingly, Epsilonbacteraeota, which only exists in autumn and winter, was discovered accidentally in the midgut. We speculated that this might participate in the nutritional supply of adult mosquitoes when temperatures drop. Wolbachia is the most abundant in autumn, accounting for 31.6% of bacteria. The content of Pantoea was highest in the summer group, which might be related to the enhancement of the ability of mosquitoes as temperatures increased. Pseudomonas is carried out as the highest level in winter. On the contrary, in spring and summer, the genus in highest abundance is Enterobacter. Acinetobacter enriches in the spring when it turns from cold to hot. By studying the diversity of midgut bacteria of Cx. quinquefasciatus, we can further understand the co-evolution of mosquitoes and their symbiotic microbes. This is necessary to discuss the seasonal variation of microorganisms and ultimately provide a new perspective for the control of Cx. quinquefasciatus to reduce the spread of the diseases which have notably vital practical significance for the effective prevention of Cx. quinquefasciatus.

Anti-mosquito properties of Pelargonium roseum (Geraniaceae) and Juniperus virginiana (Cupressaceae) essential oils against dominant malaria vectors in Africa

Background

More than 90% of malaria cases occur in Africa where the disease is transmitted by Anopheles gambiae and Anopheles arabiensis. This study evaluated the anti-mosquito properties of Juniperus virginiana (JVO) and Pelargonium roseum (PRO) essential oils (EOs) against larvae and adults of An. gambiae sensu lato (s.l.) from East Africa in laboratory and semi-field conditions.

Methods

EOs was extracted from the aerial green parts of Asian herbs by hydrodistillation. Their constituents were characterized by gas chromatography-mass spectrometry (GC-MS). Larvicidal activities of JVO, PRO, and PRO components [citronellol (CO), linalool (LO), and geraniol (GO)] were investigated against An. gambiae sensu stricto (s.s.). The percentage of knockdown effects and mortality rates of all oils were also evaluated in the adults of susceptible An. gambiae s.s. and permethrin-resistant An. arabiensis.

Results

GC-MS analyses identified major constituents of JVO (sabinene, dl-limonene, β-myrcene, bornyl acetate, and terpinen-4-ol) and PRO (citronellol, citronellyl formate, L-menthone, linalool, and geraniol). Oils showed higher larvicidal activity in the laboratory than semi-field trials. The LC₅₀ values for JVO/PRO were computed as 10.82–2.89/7.13–0.9 ppm and 10.75–9.06/13.63–8.98 ppm in laboratory and semi-field environments, respectively at exposure time of 24–72 h. The percentage of knockdown effects of the oils were also greater in An. gambiae s.s. than in An. arabiensis. Filter papers impregnated with JVO (100 ppm) and PRO (25 ppm) displayed 100% mortality rates for An. gambiae s.s. and 3.75% and 90% mortality rates, for An. arabiensis populations, respectively. Each component of CO, LO, and GO exhibited 98.13%, 97.81%, and 87.5%, respectively, and a mixture of the PRO components indicated 94.69% adult mortality to permethrin-resistant An. arabiensis.

Conclusions

The findings of this study show that PRO and its main constituents, compared to JVO, have higher anti-mosquito properties in terms of larvicidal, knockdown, and mortality when applied against susceptible laboratory and resistant wild populations of An. gambiae s.l. Consequently, these oils have the potential for the development of new, efficient, safe, and affordable agents for mosquito control.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04220-8.

Extending the lore of curcumin as dipteran Butyrylcholine esterase (BChE) inhibitor: A holistic molecular interplay assessment

Since its origin, the emergence of vector-borne infections has taken a toll on incalculable human lives. The use of chemical insecticides is one of the early known methods of vector control and although their use is still a prevalent way to combat insect population sadly the perils of insects related transmission still persists. Most commonly, the existing insecticides face the wrath of getting resisted repeatedly, paying way to develop resilient, efficient, and cost-effective natural insecticides. In this study, computational screening was performed using homology modelling, E-pharmacophore feature mapping, molecular docking, Density Function Theory (DFT) assessment, Molecular mechanics generalized Born surface area (MM-GBSA) based binding free energy calculations and Molecular Dynamics (MD) simulation to identify a potential lead phytochemical out of a manually curated library from published literature. The protein target used under this study is insect Butyrylcholine esterase (BChE). Additionally, in vitro insect (Aedes aegypti) BChE inhibition assay was also performed with the top phytochemical identified from in silico assessments. Our research highlights that curcumin leads to inhibition of enzyme BChE of Ae. aegypti. The identified mode of action of curcumin as an insect BChE inhibitor indicates the possibility of its use as an environment friendly and natural futuristic insecticide.

Overview of paratransgenesis as a strategy to control pathogen transmission by insect vectors

This article presents an overview of paratransgenesis as a strategy to control pathogen transmission by insect vectors. It first briefly summarises some of the disease-causing pathogens vectored by insects and emphasises the need for innovative control methods to counter the threat of resistance by both the vector insect to pesticides and the pathogens to therapeutic drugs. Subsequently, the state of art of paratransgenesis is described, which is a particularly ingenious method currently under development in many important vector insects that could provide an additional powerful tool for use in integrated pest control programmes. The requirements and recent advances of the paratransgenesis technique are detailed and an overview is given of the microorganisms selected for genetic modification, the effector molecules to be expressed and the environmental spread of the transgenic bacteria into wild insect populations. The results of experimental models of paratransgenesis developed with triatomines, mosquitoes, sandflies and tsetse flies are analysed. Finally, the regulatory and safety rules to be satisfied for the successful environmental release of the genetically engineered organisms produced in paratransgenesis are considered.

Gene drives gaining speed

Gene drives are selfish genetic elements that are transmitted to progeny at super-Mendelian (>50%) frequencies. Recently developed CRISPR-Cas9-based gene-drive systems are highly efficient in laboratory settings, offering the potential to reduce the prevalence of vector-borne diseases, crop pests and non-native invasive species. However, concerns have been raised regarding the potential unintended impacts of gene-drive systems. This Review summarizes the phenomenal progress in this field, focusing on optimal design features for full-drive elements (drives with linked Cas9 and guide RNA components) that either suppress target mosquito populations or modify them to prevent pathogen transmission, allelic drives for updating genetic elements, mitigating strategies including trans-complementing split-drives and genetic neutralizing elements, and the adaptation of drive technology to other organisms. These scientific advances, combined with ethical and social considerations, will facilitate the transparent and responsible advancement of these technologies towards field implementation.

Molecular detection and characterization of the endosymbiont Wolbachia in the European hedgehog flea, Archaeopsylla erinacei

Wolbachia, the endosymbiont of arthropods and onchocercid nematodes is present in many medically important insect species, being also considered for the indirect control of parasitic ones. Archaeopsylla erinacei is a flea species infesting hedgehogs acting as vector of Rickettsia felis, Bartonella henselae, and Rickettsia helvetica, thus having public health relevance. The Wolbachia surface protein (wsp) and 16S rRNA genes were used to determine the presence, prevalence and molecular typing of Wolbachia in this flea species collected in two regions of southern Italy. Of the 45 fleas tested (n = 16 males, 35.6%; n = 29 females, 64.4%), 43 (95.6%; 95% CI: 84.8-99.2) scored positive for Wolbachia, of which 15 (33.3%) and 28 (62.2%) were males and females, respectively. The sex-wise prevalence of this endosymbiont was almost equal in both sexes (males 93.8%; 95% CI: 69.5-99.7; females 96.7%; 95% CI: 83.1-99.8). Single locus sequence analysis (SLST) of Wolbachia revealed two sequence types for 16S rRNA gene, named as wAr_15227 and wAr_15234, which came from two different areas, equally distributed in male and female fleas, whilst only one sequence type was identified for wsp gene. The phylogenetic analysis placed the two 16S rRNA sequence types in paraphyletic clades belonging to the supergroup A and B, respectively. Whilst, the tree of wsp gene clustered the corresponding sequence in the same clade including those of Wolbachia supergroup A. In MLST analyses, both Wolbachia sequence types clustered in a monophyletic clade with Drosophila nikananu (wNik) and Drosophila sturtevanti (wStv) from supergroup A. ClonalFrame analysis revealed a recombination event in the wAr_15234 strain which came from Apulia region. Scientific knowledge of the presence/prevalence of Wolbachia among medically important fleas, may contribute to develop an alternative biological method for the vector control.

Diaphorina citri flavi-like virus localization, transmission, and association with Candidatus Liberibacter asiaticus in its psyllid host

Huanglongbing is caused by Candidatus Liberibacter asiaticus (CLas) and transmitted by Diaphorina citri. D. citri harbors various insect-specific viruses, including the Diaphorina citri flavi-like virus (DcFLV). The distribution and biological role of DcFLV in its host and the relationship with CLas are unknown. DcFLV was found in various organs of D. citri, including the midgut and salivary glands, where it co-localized with CLas. CLas-infected nymphs had the highest DcFLV titers compared to the infected adults and CLas-free adults and nymphs. DcFLV was vertically transmitted to offspring from female D. citri and was temporarily detected in Citrus macrophylla and grapefruit leaves from greenhouse and field. The incidences of DcFLV and CLas were positively correlated in field-collected D. citri samples, suggesting that DcFLV might be associated with CLas in the vector. These results provide new insights on the interactions between DcFLV, the D. citri, and CLas.

Wolbachia: endosymbiont of onchocercid nematodes and their vectors

Background

Wolbachia is an obligate intracellular maternally transmitted, gram-negative bacterium which forms a spectrum of endosymbiotic relationships from parasitism to obligatory mutualism in a wide range of arthropods and onchocercid nematodes, respectively. In arthropods Wolbachia produces reproductive manipulations such as male killing, feminization, parthenogenesis and cytoplasmic incompatibility for its propagation and provides an additional fitness benefit for the host to protect against pathogens, whilst in onchocercid nematodes, apart from the mutual metabolic dependence, this bacterium is involved in moulting, embryogenesis, growth and survival of the host.

Methods

This review details the molecular data of Wolbachia and its effect on host biology, immunity, ecology and evolution, reproduction, endosymbiont-based treatment and control strategies exploited for filariasis. Relevant peer-reviewed scientic papers available in various authenticated scientific data bases were considered while writing the review.

Conclusions

The information presented provides an overview on Wolbachia biology and its use in the control and/or treatment of vectors, onchocercid nematodes and viral diseases of medical and veterinary importance. This offers the development of new approaches for the control of a variety of vector-borne diseases.

Graphic Abstract

Recent advances in understanding tick and rickettsiae interactions

Ticks are haematophagous arthropods with unique molecular mechanisms for digesting host blood meal while acting as vectors for various pathogens of public health significance. The tick's pharmacologically active saliva plays a fundamental role in modulating the host's immune system for several days to weeks, depending on the tick species. The vector tick has also developed sophisticated molecular mechanisms to serve as a competent vector for pathogens, including the spotted fever group (SFG) rickettsiae. Evidence is still inadequate concerning tick-rickettsiae-host interactions and saliva-assisted transmission of the pathogen to the mammalian host. Rickettsia parkeri, of the SFG rickettsia, can cause a milder version of Rocky Mountain spotted fever known as American Boutonneuse fever. The Gulf Coast tick (Amblyomma maculatum) often transmits this pathogenic rickettsia in the USA. This review discusses the knowledge gap concerning tick-rickettsiae-host interactions by highlighting the SFG rickettsia and the Am maculatum model system. Filling this knowledge gap will provide a better understanding of the tick-rickettsiae-host interactions in disease causation, which will be crucial for developing effective methods for preventing tick-borne diseases.

The use of islands and cluster-randomized trials to investigate vector control interventions: a case study on the Bijagós archipelago, Guinea-Bissau

Vector-borne diseases threaten the health of populations around the world. While key interventions continue to provide protection from vectors, there remains a need to develop and test new vector control tools. Cluster-randomized trials, in which the intervention or control is randomly allocated to clusters, are commonly selected for such evaluations, but their design must carefully consider cluster size and cluster separation, as well as the movement of people and vectors, to ensure sufficient statistical power and avoid contamination of results. Island settings present an opportunity to conduct these studies. Here, we explore the benefits and challenges of conducting intervention studies on islands and introduce the Bijagós archipelago of Guinea-Bissau as a potential study site for interventions intended to control vector-borne diseases. This article is part of the theme issue 'Novel control strategies for mosquito-borne diseases'.

Bioactivities of rose-scented geranium nanoemulsions against the larvae of Anopheles stephensi and their gut bacteria

Anopheles stephensi with three different biotypes is a major vector of malaria in Asia. It breeds in a wide range of habitats. Therefore, safer and more sustainable methods are needed to control its immature stages rather than chemical pesticides. The larvicidal and antibacterial properties of the Pelargonium roseum essential oil (PREO) formulations were investigated against mysorensis and intermediate forms of An. stephensi in laboratory conditions. A series of nanoemulsions containing different amounts of PREO, equivalent to the calculated LC₅₀ values for each An. stephensi form, and various quantities of surfactants and co-surfactants were developed. The physical and morphological properties of the most lethal formulations were also determined. PREO and its major components, i.e. citronellol (21.34%), L-menthone (6.41%), linalool (4.214%), and geraniol (2.19%), showed potent larvicidal activity against the studied mosquitoes. The LC_50/90 values for mysorensis and intermediate forms were computed as 11.44/42.42 ppm and 12.55/47.69 ppm, respectively. The F48/F44 nanoformulations with 94% and 88% lethality for the mysorensis and intermediate forms were designated as optimized formulations. The droplet size, polydispersity index, and zeta-potential for F48/F44 were determined as 172.8/90.95 nm, 0.123/0.183, and -1.08/-2.08 mV, respectively. These results were also confirmed by TEM analysis. Prepared formulations displayed antibacterial activity against larval gut bacteria in the following order of decreasing inhibitory: LC₉₀, optimized nanoemulsions, and LC₅₀. PREO-based formulations were more effective against mysorensis than intermediate. Compared to the crude PREO, the overall larvicidal activity of all nanoformulations boosted by 20% and the optimized formulations by 50%. The sensitivity of insect gut bacteria may be a crucial factor in determining the outcome of the effect of toxins on target insects. The formulations designed in the present study may be a good option as a potent and selective larvicide for An. stephensi.

Wickerhamomyces anomalus in Mosquitoes: A Promising Yeast-Based Tool for the "Symbiotic Control" of Mosquito-Borne Diseases

The ascomycete yeast Wickerhamomyces anomalus is a mutualistic symbiont of different insects, including diptera vectors of diseases. Although fungal symbioses have been so far poorly characterized, the topic is gaining attention as yeast-insect interactions can provide pivotal information on insect biology, such as their environmental adaptation or vectorial capability. We review the symbiosis between W. anomalus and mosquitoes, which implies nutritional and protective functions. Furthermore, we focus on antiplasmodial effects of W. anomalus in malaria vectors and discuss the yeast potential for the “symbiotic control” (SC) of mosquito-borne diseases (MBDs).

Tularemia as a Mosquito-Borne Disease

Francisella tularensis (Ft) is the etiological agent of tularemia, a disease known for over 100 years in the northern hemisphere. Ft includes four subspecies, of which two are the etiologic agents of tularemia: Ft subsp. tularensis (Ftt) and Ft subsp. holarctica (Fth), mainly distributed in North America and the whole northern hemisphere, respectively. Several routes of human infection with these bacteria exist, notably through bites of Ixodidae ticks. However, mosquitoes represent the main vectors of Fth in Scandinavia, where large tularemia outbreaks have occurred, usually during the warm season. The mechanisms making mosquitoes vectors of Fth are still unclear. This review covers the inventory of research work and epidemiological data linking tularemia to mosquitoes in Scandinavia and highlights the gaps in understanding mosquitoes and Ft interactions.

Relative contributions of various endogenous and exogenous factors to the mosquito microbiota

BACKGROUND

The commensal microbiota of mosquitoes impacts their development, immunity, and competency, and could provide a target for alternative entomological control approaches. However, despite the importance of the mosquito/microbiota interactions, little is known about the relative contribution of endogenous and exogenous factors in shaping the bacterial communities of mosquitoes.

METHODS

We used a high-throughput sequencing-based assay to characterize the bacterial composition and diversity of 665 individual field-caught mosquitoes, as well as their species, genotype at an insecticide resistance locus, blood-meal composition, and the eukaryotic parasites and viruses they carry. We then used these data to rigorously estimate the individual effect of each parameter on the bacterial diversity as well as the relative contribution of each parameter to the microbial composition.

RESULTS

Overall, multivariate analyses did not reveal any significant contribution of the mosquito species, insecticide resistance, or blood meal to the bacterial composition of the mosquitoes surveyed, and infection with parasites and viruses only contributed very marginally. The main driver of the bacterial diversity was the location at which each mosquito was collected, which explained roughly 20% of the variance observed.

CONCLUSIONS

This analysis shows that when confounding factors are taken into account, the site at which the mosquitoes are collected is the main driver of the bacterial diversity of wild-caught mosquitoes, although further studies will be needed to determine which specific components of the local environment affect bacterial composition.

Essential oils and their chemical constituents against Aedes aegypti L. (Diptera: Culicidae) larvae

This review focused on the toxicity of essential oils and their constituents against Aedes aegypti L. (Diptera, Culicidae) larvae, a key vector of important arboviral diseases, such as dengue, chikungunya, zika, and yellow fever. This review is based on original articles obtained by searching major databases in the last six years. Our literature review shows that 337 essential oils from 225 plant species have been tested for larvicidal bioactivity. More than 60% of these essential oils were considered active (LC₅₀<100 µg/mL). Most species belong to the families Lamiaceae (19.3%), Lauraceae (9.9%), and Myrtaceae (9.4%). The plants studied for their larvicidal activity against A. aegypti were mainly collected in India and Brazil (30 and 20%, respectively) and the parts of the plants most used were the leaves. Less than 10% of essential oils were evaluated for toxicity against non-target organisms and with the aim to demonstrate safe use. The most used plant parts are leaves and the main compounds of essential oils were described. The most active essential oils are rich in sesquiterpene hydrocarbons, oxygenated sesquiterpenes, and monoterpene hydrocarbons. Here, factors affecting bioactivity (chemical composition, plant parts, and harvesting site) of essential oils and their constituents, as well as safety to non-target organisms are discussed. Essential oils have considerable potential against A. aegypti. This review shows that essential oils might be used to control arboviruses, and further studies on safety and formulations for application in the field should be performed.

Molecular Detection of Microorganisms Associated with Small Mammals and Their Ectoparasites in Mali

Small mammals are the natural reservoirs for many zoonotic pathogens. Using molecular tools, we assessed the prevalence of bacteria and protozoans in small mammals and their ectoparasites in Faladjè, Bougouni, and Bamoko, Mali. A total of 130 small mammals belonging to 10 different species were captured, of which 74 (56.9%) were infested by ectoparasites, including Laelaps echidnina, Xenopsylla cheopis, Amblyomma variegatum, Rhipicephalus sanguineus sensu lato, and Haemaphysalis spp. nymphs. DNA of Bartonella was found in 14/75 (18.7%), 6/48 (12.5%), and 3/7 (42.8%) small mammals from Faladjè, Bougouni, and Bamako, respectively. In Faladjè, Bartonella DNA was detected in 31/68 (45.6%) of L. echidnina and 14/22 (63.6%) of X. cheopis. In Bougouni, it was found in 2/26 (7.7%) of L. echidnina and 10/42 (23.8%) of X. cheopis. The sequences of Bartonella obtained from small mammals were close to those of Bartonella mastomydis, Bartonella elizabethae, and uncultured Bartonella spp. In Faladjè, Coxiella burnetii DNA was detected in 64.4% (29/45) of Haemaphysalis spp. ticks, 4.5% (2/44) of Mastomys erythroleucus, 12.5% (1/8) of Praomys daltoni, and 1.5% (1/68) of L. echidnina. We found DNA of Wolbachia in X. cheopis from Faladjè and DNA of Rickettsia africae and Ehrlichia ruminantium in Am. variegatum from Bougouni. The results of our study show that several small mammal species harbor and may serve as potential reservoirs of Bartonella spp., likely to play a major role in the maintenance, circulation, and potential transmission of bacteria in Mali. The pathogenicity of these bacteria for humans or animals remains to be demonstrated.

West Nile Virus: An Update on Pathobiology, Epidemiology, Diagnostics, Control and "One Health" Implications

West Nile virus (WNV) is an important zoonotic flavivirus responsible for mild fever to severe, lethal neuroinvasive disease in humans, horses, birds, and other wildlife species. Since its discovery, WNV has caused multiple human and animal disease outbreaks in all continents, except Antarctica. Infections are associated with economic losses, mainly due to the cost of treatment of infected patients, control programmes, and loss of animals and animal products. The pathogenesis of WNV has been extensively investigated in natural hosts as well as in several animal models, including rodents, lagomorphs, birds, and reptiles. However, most of the proposed pathogenesis hypotheses remain contentious, and much remains to be elucidated. At the same time, the unavailability of specific antiviral treatment or effective and safe vaccines contribute to the perpetuation of the disease and regular occurrence of outbreaks in both endemic and non-endemic areas. Moreover, globalisation and climate change are also important drivers of the emergence and re-emergence of the virus and disease. Here, we give an update of the pathobiology, epidemiology, diagnostics, control, and “One Health” implications of WNV infection and disease.

Social Determinants Predicting the Knowledge, Attitudes, and Practices of Women Toward Zika Virus Infection

Objective: To investigate the factors predicting knowledge, attitude, and practices (KAP) toward Zika virus infection among women population in Cebu City, Philippines.

Study Design: A cross-sectional survey was conducted from March 2018 to May 2018. Ethical practices were followed. A total of 702 women was approached and finally 516 completed the survey.

Methods: Descriptive analysis was undertaken for the participants' characteristics. Kolmogorov–Smirnov test was applied to declare the nature of data distribution. To determine the role of socio-demographic characteristics on KAP, differences in socio-demographic status were compared with the KAP scores using the one-way analysis of variance or Kruskal–Wallis test with p < 0.05 as significant. Logistic regression analysis was used to determine the predictors of each KAP domain (good and poor).

Results: There was a significant positive correlation between level of education and KAP scores. Also, there was a significant positive correlation between employment and KAP scores. Knowledge score was a significant predictor of practice score (b = 1.261, p = 0.024), and attitude score was also a significant predictor of practice score (b = 0.183, p = 0.039). However, knowledge score was not a significant predictor of attitude score (b = 0.316, p = 0.247).

Conclusions: The present findings provided an overall view of KAP on Zika virus infection among females in Philippines and the socio-demographic factors that affected their KAP. Women with postgraduate education and being in higher profession were the predictors influencing the KAP scores of this female population. Women with postgraduate education was the strongest predictor.

Mosquito-Borne Diseases Emergence/Resurgence and How to Effectively Control It Biologically

Deadly pathogens and parasites are transmitted by vectors and the mosquito is considered the most threatening vector in public health, transmitting these pathogens to humans and animals. We are currently witnessing the emergence/resurgence in new regions/populations of the most important mosquito-borne diseases, such as arboviruses and malaria. This resurgence may be the consequence of numerous complex parameters, but the major cause remains the mismanagement of insecticide use and the emergence of resistance. Biological control programmes have rendered promising results but several highly effective techniques, such as genetic manipulation, remain insufficiently considered as a control mechanism. Currently, new strategies based on attractive toxic sugar baits and new agents, such as Wolbachia and Asaia, are being intensively studied for potential use as alternatives to chemicals. Research into new insecticides, Insect Growth Regulators, and repellent compounds is pressing, and the improvement of biological strategies may provide key solutions to prevent outbreaks, decrease the danger to at-risk populations, and mitigate resistance.

Methodological Insight Into Mosquito Microbiome Studies

Symbiotic bacteria affect competence for pathogen transmission in insect vectors, including mosquitoes. However, knowledge on mosquito-microbiome-pathogen interactions remains limited, largely due to methodological reasons. The current, cost-effective practice of sample pooling used in mosquito surveillance and epidemiology prevents correlation of individual traits (i.e., microbiome profile) and infection status. Moreover, many mosquito studies employ laboratory-reared colonies that do not necessarily reflect the natural microbiome composition and variation in wild populations. As a consequence, epidemiological and microbiome studies in mosquitoes are to some extent uncoupled, and the interactions among pathogens, microbiomes, and natural mosquito populations remain poorly understood. This study focuses on the effect the pooling practice poses on mosquito microbiome profiles, and tests different approaches to find an optimized low-cost methodology for extensive sampling while allowing for accurate, individual-level microbiome studies. We tested the effect of pooling by comparing wild-caught, individually processed mosquitoes with pooled samples. With individual mosquitoes, we also tested two methodological aspects that directly affect the cost and feasibility of broad-scale molecular studies: sample preservation and tissue dissection. Pooling affected both alpha- and beta-diversity measures of the microbiome, highlighting the importance of using individual samples when possible. Both RNA and DNA yields were higher when using inexpensive reagents such as NAP (nucleic acid preservation) buffer or absolute ethanol, without freezing for short-term storage. Microbiome alpha- and beta-diversity did not show overall significant differences between the tested treatments compared to the controls (freshly extracted samples or dissected guts). However, the use of standardized protocols is highly recommended to avoid methodological bias in the data.

Advances in Antiwolbachial Drug Discovery for Treatment of Parasitic Filarial Worm Infections

The intracellular bacteria now known as Wolbachia were first described in filarial worms in the 1970s, but the idea of Wolbachia being used as a macrofilaricidal target did not gain wide attention until the early 2000s, with research in filariae suggesting the requirement of worms for the endosymbiont. This new-found interest prompted the eventual organization of the Anti-Wolbachia Consortium (A-WOL) at the Liverpool School of Tropical Medicine, who, among others have been active in the field of antiwolbachial drug discovery to treat filarial infections. Clinical proof of concept studies using doxycycline demonstrated the utility of the antiwolbachial therapy, but efficacious treatments were of long duration and not safe for all infected. With the advance of robotics, automation, and high-speed computing, the search for superior antiwolbachials shifted away from smaller studies with a select number of antibiotics to high-throughput screening approaches, centered largely around cell-based phenotypic screens due to the rather limited knowledge about, and tools available to manipulate, this bacterium. A concomitant effort was put towards developing validation approaches and in vivo models supporting drug discovery efforts. In this review, we summarize the strategies behind and outcomes of recent large phenotypic screens published within the last 5 years, hit compound validation approaches and promising candidates with profiles superior to doxycycline, including ones positioned to advance into clinical trials for treatment of filarial worm infections.