Ready for renascence in mosquito: The regulation of gene expression in Plasmodium sexual development

Malaria remains one of the most perilous vector-borne infectious diseases for humans globally. Sexual gametocyte represents the exclusive stage at which malaria parasites are transmitted from the vertebrate to the Anopheles host. The feasible and effective approach to prevent malaria transmission is by addressing the sexual developmental processes, that is, gametocytogenesis and gametogenesis. Thus, this review will comprehensively cover advances in the regulation of gene expression surrounding the transmissible stages, including epigenetic, transcriptional, and post-transcriptional control.

Vegetation index and livestock practices as predictors of malaria transmission in Nigeria

Nigeria is the most malaria-endemic country in the world. Vegetation and livestock practices have been linked to malaria transmission but little is known about these in Nigeria. The study aimed to evaluate the influence of vegetation and livestock as predictors of malaria transmission in Nigeria. Secondary data obtained from the Nigerian Demographic and Health Survey's Geospatial Covariate Datasets Manual were used for the analysis. The survey was carried out successfully in 1389 clusters of thirty (30) households each using a two-stage stratified random sampling design. Hierarchical beta regression models were used to model the associations between malaria incidence, enhanced vegetation index (EVI), and livestock practices. The correlation coefficients for vegetation index and livestock-related variables ranged from - 0.063 to 0.074 and varied significantly with the incidence of malaria in Nigeria (P < 0.001). The model showed vegetation index, livestock goats, and sheep as positive predictors of malaria transmission. Conversely, livestock chicken and pigs were observed to reduce the risk of malaria. The study recommends the need to take into account local differences in transmission when developing malaria early warning systems that utilize environmental and livestock predictors.

Did the prolonged residual efficacy of clothianidin products lead to a greater reduction in vector populations and subsequent malaria transmission compared to the shorter residual efficacy of pirimiphos-methyl?

BACKGROUND

The residual activity of a clothianidin + deltamethrin mixture and clothianidin alone in IRS covered more than the period of malaria transmission in northern Benin. The aim of this study was to show whether the prolonged residual efficacy of clothianidin-based products resulted in a greater reduction in vector populations and subsequent malaria transmission compared with the shorter residual efficacy of pirimiphos-methyl.

METHODS

Human bait mosquito collections by local volunteers and pyrethrum spray collections were used in 6 communes under IRS monitoring and evaluation from 2019 to 2021. ELISA/CSP and species PCR tests were performed on Anopheles gambiae sensu lato (s.l.) to determine the infectivity rate and subspecies by commune and year. The decrease in biting rate, entomological inoculation rate, incidence, inhibition of blood feeding, resting density of An. gambiae s.l. were studied and compared between insecticides per commune.

RESULTS

The An. gambiae complex was the major vector throughout the study area, acounting for 98.71% (19,660/19,917) of all Anopheles mosquitoes collected. Anopheles gambiae s.l. collected was lower inside treated houses (45.19%: 4,630/10,245) than outside (54.73%: 5,607/10,245) after IRS (p < 0.001). A significant decrease (p < 0.001) in the biting rate was observed after IRS in all departments except Donga in 2021 after IRS with clothianidin 50 WG. The impact of insecticides on EIR reduction was most noticeable with pirimiphos-methyl 300 CS, followed by the clothianidin + deltamethrin mixture and finally clothianidin 50 WG. A reduction in new cases of malaria was observed in 2020, the year of mass distribution of LLINs and IRS, as well as individual and collective protection measures linked to COVID-19. Anopheles gambiae s.l. blood-feeding rates and parous were high and similar for all insecticides in treated houses.

CONCLUSION

To achieve the goal of zero malaria, the optimal choice of vector control tools plays an important role. Compared with pirimiphos-methyl, clothianidin-based insecticides induced a lower reductions in entomological indicators of malaria transmission.

Changes in the endemic-epidemic pattern of malaria in Colombia, 1978-2021

BACKGROUND

Malaria is a major global public health issue with varying epidemiologies across countries. In Colombia, it is a priority endemic-epidemic event included in the national public health policy. However, evidence demonstrating nationwide variations in the disease behavior is limited. This study aimed to analyze changes in the levels and distribution of endemic-epidemic malaria transmission in the eco-epidemiological regions of Colombia from 1978 to 1999 and 2000 to 2021.

METHODS

We conducted a comprehensive time-series study using official secondary data on malaria-associated morbidity and mortality in Colombia from 1978 to 2021. Temporal-spatial and population variables were analyzed, and the absolute and relative frequency measures of general and regional morbidity and mortality were estimated.

RESULTS

We observed an 18% reduction in malaria endemic cases between the two study periods. The frequency and severity of the epidemic transmission of malaria varied less and were comparable across both periods. A shift was observed in the frequency of parasitic infections, with a tendency to match and increase infections by Plasmodium falciparum. The risk of malaria transmission varied significantly among the eco-epidemiological regions during both study periods. This study demonstrated a sustained decrease of 78% in malarial mortality.

CONCLUSIONS

Although the endemic components of malaria decreased slightly between the two study periods, the epidemic pattern persisted. There were significant variations in the risk of transmission across the different eco-epidemiological regions. These findings underscore the importance of targeted public health interventions in reducing malarial morbidity and mortality rates in Colombia.

Malaria in a vulnerable population living in quilombo remnant communities in the Brazilian Amazon: a cross-sectional study from 2005-2020

Quilombo remnant communities are areas officially recognized by the Brazilian government as historical communities founded by formerly enslaved individuals. These communities are mostly located in the endemic areas of malaria in the Brazilian Amazon. We retrospectively described the prevalence of malaria among individuals living in 32 recognized quilombo remnant communities in the Baiao and Oriximina municipalities located in the Para State. The number of malaria cases and the Annual Parasitic Incidence (API) recorded by the Brazilian malaria surveillance system (SIVEP-Malaria) from January 2005 to December 2020 were analyzed. We found that all communities registered at least one case over the 16-year period, the most frequent parasitic species being Plasmodium vivax (76.1%). During this period, 0.44% (4,470/1,008,714) of the malaria cases registered in Para State were reported in these quilombo remnant communities, with frequencies of 10.9% (856/7,859) in Baiao municipality and 39.1% (3,614/9,238) in Oriximina municipality, showing that individuals living in these rural communities are exposed to malaria. These data indicate that effective surveillance requires improved measures to identify malaria transmission among vulnerable populations living in quilombo remnant communities in the Brazilian Amazon.

Association of ABO, Rh-D and Kell blood groups with transfusion transmitted infections among blood donors from the Asir Region, Saudi Arabia: A retrospective observational study

OBJECTIVES

To evaluate the association between transfusion-transmitted infections (TTIs) and ABO, Rh-D, and Kell blood systems among blood donors.

METHODS

This was a retrospective study of 10,095 donors who visited the Blood Bank at Asir Hospital, Abha, Saudi Arabia. Data including demographic information, ABO, Rh-D, and Kell blood groups, and serological and molecular test results of TTIs (the TTIs were obtained from each donor's records). Chi-squared and Fisher's exact tests were employed to establish possible associations between blood groups and TTIs.

RESULTS

The prevalence rate of TTIs among donors was 6.3%, with HBcAb (70%) being the most prevalent biomarker among positive donors. Donors with the O blood group were at a higher risk of contracting TTIs. Significant associations were observed between HIV and blood group A (χ2=6.30, p=0.01), HBsAg and group AB (χ2=17.3193, p=0.00003), malaria and group A (χ2=5.0567, p=0.02), and HBV-DNA and group AB (χ2=12.3163, p=0.0004). Also, Kell blood group was significantly associated with HIV (χ2=14.5, p=0.0001), HBcAb (χ2=78.51, p<0.0001), and syphilis (χ2=25.225, p<0.00001).

CONCLUSION

ABO and Kell blood groups are associated with TTI markers. These findings highlight the need for improved strategies and approaches in screening and managing blood donations to minimize the risk of TTIs.

Impact of urbanization on the abundance and distribution of Anophelines population in Ghaziabad district, Uttar Pradesh, India

BACKGROUND OBJECTIVES

In urban areas, upsurge in population has resulted in more breeding sites for malaria vectors, and hence this scenario potentially undermine malaria elimination and control programs. The change in land use due to urbanization may result in the presence and distribution of malaria vectors. Understanding potential malaria vectors is essential for current and future malaria transmission control strategies. This study investigated the effects of rapid urbanization on malaria vectors An. culicifacies s.l. and An. stephensi L. in Ghaziabad district.

METHODS

Ghaziabad district which presents several levels of urbanization was selected for this study. Entomological investigations were conducted seasonally from 2014-2016 in the rural, urban, and peri-urban regions. Vector incrimination study was done using ELISA (confirmation by PCR) on suspected Anopheles vectors viz. An. culicifacies, An. stephensi, An. annularis and An. subpictus.

RESULTS

An. culicifacies showed alteration in distribution influenced by rural and agricultural land whereas An. stephensi was found to be influenced by artificial habitats and population growth.

INTERPRETATION CONCLUSION

The study also confirms the association between the abundance of malaria vectors and land use change.

Kenya must wake up to the threat of cryptic Anopheles species and their impact on residual malaria transmission

Malaria remains a major health problem in Kenya despite the huge efforts put in place to control it. The non-relenting malaria threat has partly been attributed to residual malaria transmission driven by vectors that cannot effectively be controlled by the two popularly applied control methods: long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). Reports indicate that residual transmission is widely spread in areas where malaria is endemic. This could mean that the World Health Organization's vision of a world free of malaria remains a mirage as elimination and prevention of re-establishment of malaria are rendered unachievable. Amongst the major contributors to residual malaria transmission are cryptic rare species, species of mosquitoes that are morphologically indistinguishable, but isolated genetically, that have not been the focus of malaria control programs. Recent studies have reported extensive new Anopheles cryptic species believed to be involved in malaria transmission in Kenya. This underscores the need to understand these malaria vector species, their distribution and bionomics and their impact on malaria transmission. This article discusses reports of these cryptic species, their importance to malaria transmission, especially in the arid and semi-arid areas, and what can be done to mitigate the situation.

Wildlife susceptibility to infectious diseases at global scales

Disease transmission prediction across wildlife is crucial for risk assessment of emerging infectious diseases. Susceptibility of host species to pathogens is influenced by the geographic, environmental, and phylogenetic context of the specific system under study. We used machine learning to analyze how such variables influence pathogen incidence for multihost pathogen assemblages, including one of direct transmission (coronaviruses and bats) and two vector-borne systems (West Nile Virus [WNV] and birds, and malaria and birds). Here we show that this methodology is able to provide reliable global spatial susceptibility predictions for the studied host-pathogen systems, even when using a small amount of incidence information (i.e., [Formula: see text] of information in a database). We found that avian malaria was mostly affected by environmental factors and by an interaction between phylogeny and geography, and WNV susceptibility was mostly influenced by phylogeny and by the interaction between geographic and environmental distances, whereas coronavirus susceptibility was mostly affected by geography. This approach will help to direct surveillance and field efforts providing cost-effective decisions on where to invest limited resources.

Discrete roles of Ir76b ionotropic coreceptor impact olfaction, blood feeding, and mating in the malaria vector mosquito Anopheles coluzzii

Anopheline mosquitoes rely on their highly sensitive chemosensory apparatus to detect diverse chemical stimuli that drive the host-seeking and blood-feeding behaviors required to vector pathogens for malaria and other diseases. This process incorporates a variety of chemosensory receptors and transduction pathways. We used advanced in vivo gene-editing and -labeling approaches to localize and functionally characterize the ionotropic coreceptor AcIr76b in the malaria mosquito Anopheles coluzzii, where it impacts both olfactory and gustatory systems. AcIr76b has a broad expression pattern in female adult antennal grooved pegs, coeloconic sensilla, and T1 and T2 sensilla on the labellum, stylets, and tarsi, as well as the larval sensory peg. AcIr76b is colocalized with the Orco odorant receptor (OR) coreceptor in a subset of cells across the female antennae and labella. In contrast to Orco and Ir8a, chemosensory coreceptors that appear essential for the activity of their respective sets of chemosensory neurons in mosquitoes, AcIr76b−/− mutants maintain wild-type peripheral responses to volatile amines on the adult palps, labellum, and larval sensory cone. Interestingly, AcIr76b−/− mutants display significantly increased responses to amines in antennal grooved peg sensilla, while coeloconic sensilla reveal significant deficits in responses to several acids and amines. Behaviorally, AcIr76b mutants manifest significantly female-specific insemination deficits, and although AcIr76b−/− mutant females can locate, alight on, and probe artificial blood hosts, they are incapable of blood feeding successfully. Taken together, our findings reveal a multidimensional functionality of Ir76b in anopheline olfactory and gustatory pathways that directly impacts the vectorial capacity of these mosquitoes.

Parous rate and longevity of anophelines mosquitoes in bure district, northwestern Ethiopia

The intensity of malaria transmission is measured by parous rate, daily survival rate, human blood meal frequency, sporozoite rate, and entomological inoculation rates. Female parous status is a key index of vector competence, adult vector longevity, recruitment rate of adult, and the length of a gonotrophic cycle. Hence, the present study was aimed to investigate the parous rate and the longevity of Anopheles mosquitoes in Bure District, Northwestern Ethiopia. Parous rate was estimated as the number of mosquitoes with parous ovaries divided by the number of females dissected multiplied by 100. Mosquito life expectancy (longevity as d) was estimated by. One way- ANOVA was applied to confirm the presence of parous rate difference in the villages (p < 0.05). A total of 952 unfed hosts-seeking Anopheles mosquitoes was dissected for parous rate determination. The overall parous rate of An. arabiensis in the district was 52.0%, and the highest parous rate was recorded in Shnebekuma than other villages (F 2, 33 = 6.974; p = 0.003). Similarly, the parous rate of An. cinereus showed significant variation among villages (F 2, 33 = 5.044, p = 0.012) and the highest rate (63.0%) was recorded in Bukta. The mean longevity of An. funestus, An. arabiensis, An. coustani, An. squamosus, An. pharoensis, and An. cinereus was 6.5 days, 4.6 days, 3.5 days, 3.7 days, 2.7 days, and 2.2 days, respectively. The longevity of each species was not sufficient to complete the life cycle of malaria parasite for malaria transmission throughout the year because P. falciparum requires from 12–14 day.

Primate malarias as a model for cross-species parasite transmission

Parasites regularly switch into new host species, representing a disease burden and conservation risk to the hosts. The distribution of these parasites also gives insight into characteristics of ecological networks and genetic mechanisms of host-parasite interactions. Some parasites are shared across many species, whereas others tend to be restricted to hosts from a single species. Understanding the mechanisms producing this distribution of host specificity can enable more effective interventions and potentially identify genetic targets for vaccines or therapies. As ecological connections between human and local animal populations increase, the risk to human and wildlife health from novel parasites also increases. Which of these parasites will fizzle out and which have the potential to become widespread in humans? We consider the case of primate malarias, caused by Plasmodium parasites, to investigate the interacting ecological and evolutionary mechanisms that put human and nonhuman primates at risk for infection. Plasmodium host switching from nonhuman primates to humans led to ancient introductions of the most common malaria-causing agents in humans today, and new parasite switching is a growing threat, especially in Asia and South America. Based on a wild host-Plasmodium occurrence database, we highlight geographic areas of concern and potential areas to target further sampling. We also discuss methodological developments that will facilitate clinical and field-based interventions to improve human and wildlife health based on this eco-evolutionary perspective.

The neglected role of relative humidity in the interannual variability of urban malaria in Indian cities

The rapid pace of urbanization makes it imperative that we better understand the influence of climate forcing on urban malaria transmission. Despite extensive study of temperature effects in vector-borne infections in general, consideration of relative humidity remains limited. With process-based dynamical models informed by almost two decades of monthly surveillance data, we address the role of relative humidity in the interannual variability of epidemic malaria in two semi-arid cities of India. We show a strong and significant effect of humidity during the pre-transmission season on malaria burden in coastal Surat and more arid inland Ahmedabad. Simulations of the climate-driven transmission model with the MLE (Maximum Likelihood Estimates) of the parameters retrospectively capture the observed variability of disease incidence, and also prospectively predict that of 'out-of-fit' cases in more recent years, with high accuracy. Our findings indicate that relative humidity is a critical factor in the spread of urban malaria and potentially other vector-borne epidemics, and that climate change and lack of hydrological planning in cities might jeopardize malaria elimination efforts.

Blood meal analysis of Anopheles vectors of simian malaria based on laboratory and field studies

Blood feeding and host-seeking behaviors of a mosquito play an imperative role in determining its vectorial capacity in transmitting pathogens. Unfortunately, limited information is available regarding blood feeding behavior of Anopheles species in Malaysia. Collection of resting Anopheles mosquitoes for blood meal analysis poses a great challenge especially for forest dwelling mosquitoes. Therefore, a laboratory-based study was conducted to evaluate the potential use of mosquitoes caught using human landing catch (HLC) for blood meal analysis, and subsequently to document blood feeding behavior of local Anopheles mosquitoes in Peninsular Malaysia. The laboratory-based experiment from this study revealed that mosquitoes caught using HLC had the potential to be used for blood meal analysis. Besides HLC, mosquitoes were also collected using manual aspirator and Mosquito Magnet. Overall, 47.4% of 321 field-caught Anopheles mosquitoes belonging to six species were positive for vertebrate host DNA in their blood meal. The most frequent blood meal source was human (45.9%) followed by wild boar (27.4%), dog (15.3%) and monkey (7.5%). Interestingly, only Anopheles cracens and Anopheles introlatus (Leucosphyrus Group) fed on monkey. This study further confirmed that members of the Leucosphyrus Group are the predominant vectors for knowlesi malaria transmission in Peninsular Malaysia mainly due to their simio-anthropophagic feeding behavior.

Molecular Characterization of a Vector-Based Candidate Antigen Using the 3'-RACE and Genome Walking Methods and In Silico Analysis of the Correspondent Protein for Vaccine Design and Development

The main objectives of developing vaccines to prevent malaria transmission are malaria control and preventing the reemergence of the disease in endemic regions. Molecular and in silico characterization of a candidate molecule is the first step in the vaccine design process. Determining the sequence and amplification of full-length cDNA copies from the mRNA transcripts is often challenging. The methods in this chapter provide a protocol for the rapid amplification of cDNA ends (RACE) and genome walking. Carboxypeptidase B2 enzyme from A. stephensi (CPBAs-2) was selected as the target molecule and the steps in its characterization and in silico analysis are explained in this chapter.

Anopheles salivary antigens as serological biomarkers of vector exposure and malaria transmission: A systematic review with multilevel modelling

Background

Entomological surveillance for malaria is inherently resource-intensive and produces crude population-level measures of vector exposure which are insensitive in low-transmission settings. Antibodies against Anopheles salivary proteins measured at the individual level may serve as proxy biomarkers for vector exposure and malaria transmission, but their relationship is yet to be quantified.

Methods

A systematic review of studies measuring antibodies against Anopheles salivary antigens (PROSPERO: CRD42020185449). Multilevel modelling (to account for multiple study-specific observations [level 1], nested within study [level 2], and study nested within country [level 3]) estimated associations between seroprevalence with Anopheles human biting rate (HBR) and malaria transmission measures.

Results

From 3981 studies identified in literature searches, 42 studies across 16 countries were included contributing 393 study-specific observations of anti-Anopheles salivary antibodies determined in 42,764 samples. A positive association between HBR (log transformed) and seroprevalence was found; overall a twofold (100% relative) increase in HBR was associated with a 23% increase in odds of seropositivity (OR: 1.23, 95% CI: 1.10-1.37; p<0.001). The association between HBR and Anopheles salivary antibodies was strongest with concordant, rather than discordant, Anopheles species. Seroprevalence was also significantly positively associated with established epidemiological measures of malaria transmission: entomological inoculation rate, Plasmodium spp. prevalence, and malarial endemicity class.

Conclusions

Anopheles salivary antibody biomarkers can serve as a proxy measure for HBR and malaria transmission, and could monitor malaria receptivity of a population to sustain malaria transmission. Validation of Anopheles species-specific biomarkers is important given the global heterogeneity in the distribution of Anopheles species. Salivary biomarkers have the potential to transform surveillance by replacing impractical, inaccurate entomological investigations, especially in areas progressing towards malaria elimination.

Funding

Australian National Health and Medical Research Council, Wellcome Trust.

Integration of whole genome sequencing and transcriptomics reveals a complex picture of the reestablishment of insecticide resistance in the major malaria vector Anopheles coluzzii

Insecticide resistance is a major threat to gains in malaria control, which have been stalling and potentially reversing since 2015. Studies into the causal mechanisms of insecticide resistance are painting an increasingly complicated picture, underlining the need to design and implement targeted studies on this phenotype. In this study, we compare three populations of the major malaria vector An. coluzzii: a susceptible and two resistant colonies with the same genetic background. The original colonised resistant population rapidly lost resistance over a 6-month period, a subset of this population was reselected with pyrethroids, and a third population of this colony that did not lose resistance was also available. The original resistant, susceptible and re-selected colonies were subject to RNAseq and whole genome sequencing, which identified a number of changes across the transcriptome and genome linked with resistance. Firstly, an increase in the expression of genes within the oxidative phosphorylation pathway were seen in both resistant populations compared to the susceptible control; this translated phenotypically through an increased respiratory rate, indicating that elevated metabolism is linked directly with resistance. Genome sequencing highlighted several blocks clearly associated with resistance, including the 2Rb inversion. Finally, changes in the microbiome profile were seen, indicating that the microbial composition may play a role in the resistance phenotype. Taken together, this study reveals a highly complicated phenotype in which multiple transcriptomic, genomic and microbiome changes combine to result in insecticide resistance.

Insecticide resistance in major malaria vectors represents the single biggest threat to malaria control programs, which are heavily reliant upon insecticide-based interventions. Studying resistance using multi-omics approaches has proven difficult due to the use of susceptible comparator populations that have been colonised in a laboratory setting for decades, leading to substantial noise in the data due to differing genetic backgrounds. Here, we utilise a resistant Anopheles coluzzii population from Burkina Faso, a derived population that rapidly lost resistance over a 6-month period, and a population re-selected after loss of resistance to explore causative mechanisms of insecticide resistance. To determine the underlying cause of this phenotype, we use RNAseq, whole genome sequencing and lab-based validation to show changes in respiratory rate, wide-ranging genomic changes and alterations in the microbiome are linked to resistance in this population. These findings demonstrate the complexity of resistance and the challenges in utilising diagnostic markers for resistance in a field setting.

Barcoded Asaia bacteria enable mosquito in vivo screens and identify novel systemic insecticides and inhibitors of malaria transmission

This work addresses the need for new chemical matter in product development for control of pest insects and vector-borne diseases. We present a barcoding strategy that enables phenotypic screens of blood-feeding insects against small molecules in microtiter plate-based arrays and apply this to discovery of novel systemic insecticides and compounds that block malaria parasite development in the mosquito vector. Encoding of the blood meals was achieved through recombinant DNA-tagged Asaia bacteria that successfully colonised Aedes and Anopheles mosquitoes. An arrayed screen of a collection of pesticides showed that chemical classes of avermectins, phenylpyrazoles, and neonicotinoids were enriched for compounds with systemic adulticide activity against Anopheles. Using a luminescent Plasmodium falciparum reporter strain, barcoded screens identified 48 drug-like transmission-blocking compounds from a 400-compound antimicrobial library. The approach significantly increases the throughput in phenotypic screening campaigns using adult insects and identifies novel candidate small molecules for disease control.

This study presents a barcoding strategy that enables high-throughput phenotypic screens of blood-feeding insects against small molecules in microtiter plate-based arrays and applies this to the discovery of novel systemic insecticides and compounds that block malaria parasite development in the mosquito vector.

Molecular Analysis Reveals a High Diversity of Anopheline Mosquitoes in Yanomami Lands and the Pantanal Region of Brazil

Identifying the species of the subfamily Anophelinae that are Plasmodium vectors is important to vector and malaria control. Despite the increase in cases, vector mosquitoes remain poorly known in Brazilian indigenous communities. This study explores Anophelinae mosquito diversity in the following areas: (1) a Yanomami reserve in the northwestern Amazon Brazil biome and (2) the Pantanal biome in southwestern Brazil. This is carried out by analyzing cytochrome c oxidase (COI) gene data using Refined Single Linkage (RESL), Assemble Species by Automatic Partitioning (ASAP), and tree-based multi-rate Poisson tree processes (mPTP) as species delimitation approaches. A total of 216 specimens collected from the Yanomami and Pantanal regions were sequenced and combined with 547 reference sequences for species delimitation analyses. The mPTP analysis for all sequences resulted in the delimitation of 45 species groups, while the ASAP analysis provided the partition of 48 groups. RESL analysis resulted in 63 operational taxonomic units (OTUs). This study expands our scant knowledge of anopheline species in the Yanomami and Pantanal regions. At least 18 species of Anophelinae mosquitoes were found in these study areas. Additional studies are now required to determine the species that transmit Plasmodium spp. in these regions.

Drug targeting of aminoacyl-tRNA synthetases in Anopheles species and Aedes aegypti that cause malaria and dengue

BACKGROUND

Mosquito-borne diseases have a devastating impact on human civilization. A few species of Anopheles mosquitoes are responsible for malaria transmission, and while there has been a reduction in malaria-related deaths worldwide, growing insecticide resistance is a cause for concern. Aedes mosquitoes are known vectors of viral infections, including dengue, yellow fever, chikungunya, and Zika. Aminoacyl-tRNA synthetases (aaRSs) are key players in protein synthesis and are potent anti-infective drug targets. The structure-function activity relationship of aaRSs in mosquitoes (in particular, Anopheles and Aedes spp.) remains unexplored.

METHODS

We employed computational techniques to identify aaRSs from five different mosquito species (Anopheles culicifacies, Anopheles stephensi, Anopheles gambiae, Anopheles minimus, and Aedes aegypti). The VectorBase database ( https://vectorbase.org/vectorbase/app ) and web-based tools were utilized to predict the subcellular localizations (TargetP-2.0, UniProt, DeepLoc-1.0), physicochemical characteristics (ProtParam), and domain arrangements (PfAM, InterPro) of the aaRSs. Structural models for prolyl (PRS)-, and phenylalanyl (FRS)-tRNA synthetases-were generated using the I-TASSER and Phyre protein modeling servers.

RESULTS

Among the vector species, a total of 37 (An. gambiae), 37 (An. culicifacies), 37 (An. stephensi), 37 (An. minimus), and 35 (Ae. aegypti) different aaRSs were characterized within their respective mosquito genomes. Sequence identity amongst the aaRSs from the four Anopheles spp. was > 80% and in Ae. aegypti was > 50%.

CONCLUSIONS

Structural analysis of two important aminoacyl-tRNA synthetases [prolyl (PRS) and phenylanalyl (FRS)] of Anopheles spp. suggests structural and sequence similarity with potential antimalarial inhibitor [halofuginone (HF) and bicyclic azetidine (BRD1369)] binding sites. This suggests the potential for repurposing of these inhibitors against the studied Anopheles spp. and Ae. aegypti.

Genetic diversity of Anopheles stephensi in Ethiopia provides insight into patterns of spread

BACKGROUND

The recent detection of the South Asian malaria vector Anopheles stephensi in the Horn of Africa (HOA) raises concerns about the impact of this mosquito on malaria transmission in the region. Analysis of An. stephensi genetic diversity and population structure can provide insight into the history of the mosquito in the HOA to improve predictions of future spread. We investigated the genetic diversity of An. stephensi in eastern Ethiopia, where detection suggests a range expansion into this region, in order to understand the history of this invasive population.

METHODS

We sequenced the cytochrome oxidase subunit I (COI) and cytochrome B gene (CytB) in 187 An. stephensi collected from 10 sites in Ethiopia in 2018. Population genetic, phylogenetic, and minimum spanning network analyses were conducted for Ethiopian sequences. Molecular identification of blood meal sources was also performed using universal vertebrate CytB sequencing.

RESULTS

Six An. stephensi COI-CytB haplotypes were observed, with the highest number of haplotypes in the northeastern sites (Semera, Bati, and Gewana towns) relative to the southeastern sites (Kebridehar, Godey, and Degehabur) in eastern Ethiopia. We observed population differentiation, with the highest differentiation between the northeastern sites compared to central sites (Erer Gota, Dire Dawa, and Awash Sebat Kilo) and the southeastern sites. Phylogenetic and network analysis revealed that the HOA An. stephensi are more genetically similar to An. stephensi from southern Asia than from the Arabian Peninsula. Finally, molecular blood meal analysis revealed evidence of feeding on cows, goats, dogs, and humans, as well as evidence of multiple (mixed) blood meals.

CONCLUSION

We show that An. stephensi is genetically diverse in Ethiopia and with evidence of geographical structure. Variation in the level of diversity supports the hypothesis for a more recent introduction of An. stephensi into southeastern Ethiopia relative to the northeastern region. We also find evidence that supports the hypothesis that HOA An. stephensi populations originate from South Asia rather than the Arabian Peninsula. The evidence of both zoophagic and anthropophagic feeding support the need for additional investigation into the potential for livestock movement to play a role in vector spread in this region.

Emulator-based Bayesian optimization for efficient multi-objective calibration of an individual-based model of malaria

Individual-based models have become important tools in the global battle against infectious diseases, yet model complexity can make calibration to biological and epidemiological data challenging. We propose using a Bayesian optimization framework employing Gaussian process or machine learning emulator functions to calibrate a complex malaria transmission simulator. We demonstrate our approach by optimizing over a high-dimensional parameter space with respect to a portfolio of multiple fitting objectives built from datasets capturing the natural history of malaria transmission and disease progression. Our approach quickly outperforms previous calibrations, yielding an improved final goodness of fit. Per-objective parameter importance and sensitivity diagnostics provided by our approach offer epidemiological insights and enhance trust in predictions through greater interpretability.

Malaria infection and anemia status in under-five children from Southern Tanzania where seasonal malaria chemoprevention is being implemented

Background

Malaria and anemia remain major public health challenges in Tanzania. Household socioeconomic factors are known to influence these conditions. However, it is not clear how these factors influence malaria transmission and anemia in Masasi and Nanyumbu Districts. This study presents findings on malaria and anemia situation in under-five children and its influencing socioeconomic factors in Masasi and Nanyumbu Districts, surveyed as part of an ongoing seasonal malaria chemoprevention operational study.

Methods

A community-based cross-sectional survey was conducted between August and September 2020. Finger-prick blood samples collected from children aged 3–59 months were used to test for malaria infection using malaria rapid diagnostic test (mRDT), thick smears for determination of asexual and sexual parasitemia, and thin smear for parasite speciation. Hemoglobin concentration was measured using a HemoCue spectrophotometer. A structured questionnaire was used to collect household socioeconomic information from parents/caregivers of screened children. The prevalence of malaria was the primary outcome. Chi-square tests, t-tests, and logistic regression models were used appropriately.

Results

Overall mRDT-based malaria prevalence was 15.9% (373/2340), and was significantly higher in Nanyumbu (23.7% (167/705) than Masasi District (12.6% (206/1635), p<0.001. Location (Nanyumbu), no formal education, household number of people, household number of under-fives, not having a bed net, thatched roof, open/partially open eave, sand/soil floor, and low socioeconomic status were major risks for malaria infection. Some 53.9% (1196/2218) children had anemia, and the majority were in Nanyumbu (63.5% (458/705), p<0.001. Location (Nanyumbu), mRDT positive, not owning a bed net, not sleeping under bed net, open/partially open eave, thatched window, sex of the child, and age of the child were major risk factors for anemia.

Conclusion

Prevalence of malaria and anemia was high and was strongly associated with household socioeconomic factors. Improving household socioeconomic status is expected to reduce the prevalence of the conditions in the area.

Comment on: Emergence of the invasive malaria vector Anopheles stephensi in Khartoum State, Central Sudan

This letter comments on the article "Emergence of the invasive malaria vector Anopheles stephensi in Khartoum State, Central Sudan" published in Parasites and Vectors 2021, 14:511. Here we aim of provide a response to this paper in the broader context of the invasion and spread of An. stephensi in the Horn of Africa, and the required response to it. We agree with the authors that the arrival of this invasive vector in Khartoum State is of high public health concern. Equally concerning, however, we found that the detection of the vector by the authors in 2018 seemingly took 3 years to communicate to the Ministry of Health and World Health Organization (WHO), and was reliant on an academic journal. We consider that this short report sets a poor example of how public health threats should be reported. Suitable communication alternatives to alert public health authorities to such threats have been put in place by the WHO and its Member States, and are well known to at least some of the authors of the short report. We would like to encourage all readers not to follow the example of Ahmed et al. but instead act as responsible public health professionals by drawing on the established reporting mechanisms and escalate potential threats as soon as they are identified.

Phylogenetic analysis of the Neotropical Albitarsis Complex based on mitogenome data

BACKGROUND

Some of the most important malaria vectors in South America belong to the Albitarsis Complex (Culicidae; Anophelinae; Anopheles). Understanding the origin, nature, and geographical distribution of species diversity in this important complex has important implications for vector incrimination, control, and management, and for modelling future responses to climate change, deforestation, and human population expansion. This study attempts to further explore species diversity and evolutionary history in the Albitarsis Complex by undertaking a characterization and phylogenetic analysis of the mitogenome of all 10 putative taxa in the Albitarsis Complex.

METHODS

Mitogenome assembly and annotation allowed for feature comparison among Albitarsis Complex and Anopheles species. Selection analysis was conducted across all 13 protein-coding genes. Maximum likelihood and Bayesian inference methods were used to construct gene and species trees, respectively. Bayesian methods were also used to jointly estimate species delimitation and species trees.

RESULTS

Gene composition and order were conserved across species within the complex. Unique signatures of positive selection were detected in two species-Anopheles janconnae and An. albitarsis G-which may have played a role in the recent and rapid diversification of the complex. The COI gene phylogeny does not fully recover the mitogenome phylogeny, and a multispecies coalescent-based phylogeny shows that considerable uncertainty exists through much of the mitogenome species tree. The origin of divergence in the complex dates to the Pliocene/Pleistocene boundary, and divergence within the distinct northern South American clade is estimated at approximately 1 million years ago. Neither the phylogenetic trees nor the delimitation approach rejected the 10-species hypothesis, although the analyses could not exclude the possibility that four putative species with scant a priori support (An. albitarsis G, An. albitarsis H, An. albitarsis I, and An. albitarsis J), represent population-level, rather than species-level, splits.

CONCLUSION

The lack of resolution in much of the species tree and the limitations of the delimitation analysis warrant future studies on the complex using genome-wide data and the inclusion of additional specimens, particularly from two putative species, An. albitarsis I and An. albitarsis J.

Malaria awareness of adults in high, moderate and low transmission settings: A cross-sectional study in rural East Nusa Tenggara Province, Indonesia

Introduction

The 2009 Indonesian roadmap to malaria elimination indicated that the nation had been progressing towards achieving malaria elimination by 2030. Currently, most of the districts in the western part of Indonesia have eliminated malaria; however, none of the districts in the East Nusa Tenggara Province (ENTP) have met these set targets. This study aimed to investigate the status of malaria awareness of rural adults in the ENTP.

Methods

A community-based cross-sectional study was conducted between October and December 2019 in high, moderate, and low malaria-endemic settings (MESs) in the ENTP. After obtaining informed consent, data were collected using an interviewer-administered structure questionnaire among 1503 participants recruited by a multi-stage cluster sampling method. A malaria awareness index was developed based on ten questions. A binary logistic regression method was applied to investigate the significance of any association between malaria awareness and the different MESs.

Results

The participation rate of the study was 99.5%. Of this number, 51.4% were female and 45.5% had completed primary education. The malaria awareness index was significantly low (48.8%, 95% confidence interval [CI]: 45.2–52.4). Malaria awareness of rural adults residing in low endemic settings was two times higher than for those living in high endemic settings (adjusted odds ratio [AOR]: 2.41, 95% CI: 1.81–3.21) and the basic malaria knowledge of participants living in low malaria-endemic settings was almost four times higher than that in high endemic settings (AOR: 3.75, 95% CI: 2.75–5.11). Of the total participants, 81.3% (95% CI: 79.1–83.5) were aware that malaria could be prevented and 75.1% (95% CI: 72.6–77.6) knew at least one prevention measure. Overall, the awareness of fever as the main symptom of malaria, mosquito bites as the transmission mode of malaria, and seeking treatment within 24 hours of suffering from malaria was poor at 37.9% (95% CI: 33.9–41.9), 59.1% (95% CI: 55.9–62.3), and 46.0% (95% CI: 42.3–49.7), respectively. The poor level of awareness was significantly different amongst the three MESs, with the lowest levels of awareness in the high endemic setting.

Conclusion

Malaria awareness of rural adults needs to be improved to address Indonesia’s national roadmap for malaria elimination. Results indicated that public health programs at a local government level should incorporate the malaria awareness index in their key strategic intervention to address malaria awareness.

The cytochrome P450 CYP325A is a major driver of pyrethroid resistance in the major malaria vector Anopheles funestus in Central Africa

The overexpression and overactivity of key cytochrome P450s (CYP450) genes are major drivers of metabolic resistance to insecticides in African malaria vectors such as Anopheles funestus s.s. Previous RNAseq-based transcription analyses revealed elevated expression of CYP325A specific to Central African populations but its role in conferring resistance has not previously been demonstrated. In this study, RT-qPCR consistently confirmed that CYP325A is highly over-expressed in pyrethroid-resistant An. funestus from Cameroon, compared with a control strain and insecticide-unexposed mosquitoes. A synergist bioassay with PBO significantly recovered susceptibility for permethrin and deltamethrin indicating P450-based metabolic resistance. Analyses of the coding sequence of CYP325A Africa-wide detected high-levels of polymorphism, but with no predominant alleles selected by pyrethroid resistance. Geographical amino acid changes were detected notably in Cameroon. In silico homology modelling and molecular docking simulations predicted that CYP325A binds and metabolises type I and type II pyrethroids. Heterologous expression of recombinant CYP325A and metabolic assays confirmed that the most-common Cameroonian haplotype metabolises both type I and type II pyrethroids with depletion rate twice that the of the DR Congo haplotype. Analysis of the 1 kb putative promoter of CYP325A revealed reduced diversity in resistant mosquitoes compared to susceptible ones, suggesting a potential selective sweep in this region. The establishment of CYP325A as a pyrethroid resistance metabolising gene further explains pyrethroid resistance in Central African populations of An. funestus. Our work will facilitate future efforts to detect the causative resistance markers in the promoter region of CYP325A to design field applicable DNA-based diagnostic tools.

Spatio-temporal analysis and prediction of malaria cases using remote sensing meteorological data in Diébougou health district, Burkina Faso, 2016-2017

Malaria control and prevention programs are more efficient and cost-effective when they target hotspots or select the best periods of year to implement interventions. This study aimed to identify the spatial distribution of malaria hotspots at the village level in Diébougou health district, Burkina Faso, and to model the temporal dynamics of malaria cases as a function of meteorological conditions and of the distance between villages and health centres (HCs). Case data for 27 villages were collected in 13 HCs. Meteorological data were obtained through remote sensing. Two synthetic meteorological indicators (SMIs) were created to summarize meteorological variables. Spatial hotspots were detected using the Kulldorf scanning method. A General Additive Model was used to determine the time lag between cases and SMIs and to evaluate the effect of SMIs and distance to HC on the temporal evolution of malaria cases. The multivariate model was fitted with data from the epidemic year to predict the number of cases in the following outbreak. Overall, the incidence rate in the area was 429.13 cases per 1000 person-year with important spatial and temporal heterogeneities. Four spatial hotspots, involving 7 of the 27 villages, were detected, for an incidence rate of 854.02 cases per 1000 person-year. The hotspot with the highest risk (relative risk = 4.06) consisted of a single village, with an incidence rate of 1750.75 cases per 1000 person-years. The multivariate analysis found greater variability in incidence between HCs than between villages linked to the same HC. The time lag that generated the better predictions of cases was 9 weeks for SMI1 (positively correlated with precipitation variables) and 16 weeks for SMI2 (positively correlated with temperature variables. The prediction followed the overall pattern of the time series of reported cases and predicted the onset of the following outbreak with a precision of less than 3 weeks. This analysis of malaria cases in Diébougou health district, Burkina Faso, provides a powerful prospective method for identifying and predicting high-risk areas and high-transmission periods that could be targeted in future malaria control and prevention campaigns.

Efficacy of targeted indoor residual spraying with the pyrrole insecticide chlorfenapyr against pyrethroid-resistant Aedes aegypti

Background

There is an increased need to mitigate the emergence of insecticide resistance and incorporate new formulations and modes of application to control the urban vector Aedes aegypti. Most research and development of insecticide formulations for the control of Ae. aegypti has focused on their peridomestic use as truck-mounted ULV-sprays or thermal fogs despite the widespread knowledge that most resting Ae. aegypti are found indoors. A recent modification of indoor residual spraying (IRS), termed targeted IRS (TIRS) works by restricting applications to 1.5 m down to the floor and on key Ae. aegypti resting sites (under furniture). TIRS also opens the possibility of evaluating novel residual insecticide formulations currently being developed for malaria IRS.

Methods

We evaluated the residual efficacy of chlorfenapyr, formulated as Sylando 240SC, for 12 months on free-flying field-derived pyrethroid-resistant Ae. aegypti using a novel experimental house design in Merida, Mexico. On a monthly basis, 600 female Ae. aegypti were released into the houses and left indoors with access to sugar solution for 24 hours. After the exposure period, dead and alive mosquitoes were counted in houses treated with chlorfenapyr as well as untreated control houses to calculate 24-h mortality. An evaluation for these exposed cohorts of surviving mosquitoes was extended up to seven days under laboratory conditions to quantify “delayed mortality”.

Results

Mean acute (24-h) mortality of pyrethroid-resistant Ae. aegypti ranged 80–97% over 5 months, dropping below 30% after 7 months post-TIRS. If delayed mortality was considered (quantifying mosquito mortality up to 7 days after exposure), residual efficacy was above 90% for up to 7 months post-TIRS application. Generalized Additive Mixed Models quantified a residual efficacy of chlorfenapyr of 225 days (ca. 7.5 months).

Conclusions

Chlorfenapyr represents a new option for TIRS control of Ae. aegypti in urban areas, providing a highly-effective time of protection against indoor Ae. aegypti females of up to 7 months.

Vector control (VC) for managing Aedes aegypti and reducing transmission of Aedes-borne diseases is largely focused on peridomestic insecticide applications. However, the indoor resting behavior of Ae. aegypti and the acceleration of insecticide resistance owed to reduced modes of action have diminished the effectiveness of many VC tools. A targeted Indoor residual spraying (TIRS) modality in experimental housing units was employed to investigate the potential of chlorfenapyr, a pyrrole-class insecticide with known effectiveness to resistant mosquito species. This was the first investigation for chlorfenapyr use against locally resistant Ae. aegypti (Merida, Mexico) with this approach. Two treatment arms were investigated in the present study: TIRS and a control house where only water was sprayed. A comparison of entomological efficacy for TIRS applied to interior perimeter walls below 1.5 m with chlorfenapyr (formulated as Sylando 240SC) at 250 mg/m² over 12 months was assessed. TIRS chlorfenapyr treatments were highly efficacious and led to acute mortalities (after 24 exposure) above 80% up to 5 months; delayed mortalities (to Ae. aegypti) were monitored over seven days post exposures vs untreated controls. When delayed mortality was considered, residual efficacy of chlorfenapyr extended to 7 months. These data provide evidence that TIRS chlorfenapyr is an effective Aedes management tool that surpassed efficacy profiles for other TIRS insecticides that have been previously reported with this method. Further, Chlorfenapyr emerges as a novel addition to Ae. aegypti VC, and future studies should focus on its effectiveness and residual power as part of Phase II-III TIRS trials.

Defeating malaria in the North-East region: the forerunner for malaria elimination in India

India is a malaria endemic country which is targeting malaria elimination by 2027. Transmission intensities are low-to-moderate depending on the region supported by multiple disease vectors. Among these, comparatively North-East India contributes to high proportions of malaria cases annually, the majority of which are due to Plasmodium falciparum (90%). Anopheles minimus and An. baimaii (sibling species in the An. dirus complex) are widely prevalent and incriminated as vectors of malaria. Number of intervention tools were field-evaluated beginning 1988 to date against disease vectors and causative parasites to contain the spread of malaria. These included (i) insecticide-treated netting materials (ITNs) for vector control, (ii) rapid diagnostic tests (RDTs) for in situ diagnosis, and (iii) therapeutic efficacy of artemisinin-based combination therapies (ACTs) for improved drug-policy; all of which were incorporated in healthcare services resulting in substantial disease transmission reduction. Populations of both An. minimus and An. baimaii were observed depleting, instead An. culicifacies s.l. recorded to be fast invading degraded forests and assessed to be resistant to multiple insecticides. Of the two prevalent Plasmodium species, while P. vivax continued to be susceptible to chloroquine therapy, P. falciparum had emerged resistant to most available antimalarial drugs except ACTs over space and time and spreading to peninsular India threatening elimination efforts. Disease transmission trends were observed to be declining for which the state of Assam has made huge strides reporting steady fall in cases each passing year vis-à-vis Meghalaya, Mizoram and Tripura (all sharing international border with Bangladesh), in which malaria transmission remained uninterrupted. Consequently, control of malaria in the North-East region of India is of immediate importance and needs prioritization for intensified disease surveillance and control interventions coupled with improved access to healthcare services mitigating risk of disease outbreaks and spread of drug-resistant malaria helping realize the goal of malaria elimination in the country.

Nonrandom Selection and Multiple Blood Feeding of Human Hosts by Anopheles Vectors: Implications for Malaria Transmission in Papua New Guinea

Nonrandom selection and multiple blood feeding of human hosts by Anopheles mosquitoes may exacerbate malaria transmission. Both patterns of blood feeding and their relationship to malaria epidemiology were investigated in Anopheles vectors in Papua New Guinea (PNG). Blood samples from humans and mosquito blood meals were collected in villages and human genetic profiles ("fingerprints") were analyzed by genotyping 23 microsatellites and a sex-specific marker. Frequency of blood meals acquired from different humans, identified by unique genetic profiles, was fitted to Poisson and negative binomial distributions to test for nonrandom patterns of host selection. Blood meals with more than one genetic profiles were classified as mosquitoes that fed on multiple humans. The age of a person bitten by a mosquito was determined by matching the blood-meal genetic profile to the villagers' genetic profiles. Malaria infection in humans was determined by PCR test of blood samples. The results show nonrandom distribution of blood feeding among humans, with biased selection toward males and individuals aged 15-30 years. Prevalence of Plasmodium falciparum infection was higher in this age group, suggesting males in this age range could be super-spreaders of malaria parasites. The proportion of mosquitoes that fed on multiple humans ranged from 6% to 13% among villages. The patterns of host utilization observed here can amplify transmission and contribute to the persistence of malaria in PNG despite efforts to suppress it with insecticidal bed nets. Excessive feeding on males aged 15-30 years underscores the importance of targeted interventions focusing on this demographic group.

Population genetic structure of the malaria vector Anopheles minimus in Thailand based on mitochondrial DNA markers

BACKGROUND

The malaria vector Anopheles minimus has been influenced by external stresses affecting the survival rate and vectorial capacity of the population. Since An. minimus habitats have continuously undergone ecological changes, this study aimed to determine the population genetic structure and the potential gene flow among the An. minimus populations in Thailand.

METHODS

Anopheles minimus was collected from five malaria transmission areas in Thailand using Centers for Disease Control and Prevention (CDC) light traps. Seventy-nine females from those populations were used as representative samples. The partial mitochondrial cytochrome c oxidase subunit I (COI), cytochrome c oxidase subunit II (COII) and cytochrome b (Cytb) gene sequences were amplified and analyzed to identify species and determine the current population genetic structure. For the past population, we determined the population genetic structure from the 60 deposited COII sequences in GenBank of An. minimus collected from Thailand 20 years ago.

RESULTS

The current populations of An. minimus were genetically divided into two lineages, A and B. Lineage A has high haplotype diversity under gene flow similar to the population in the past. Neutrality tests suggested population expansion of An. minimus, with the detection of abundant rare mutations in all populations, which tend to arise from negative selection.

CONCLUSIONS

This study revealed that the population genetic structure of An. minimus lineage A was similar between the past and present populations, indicating high adaptability of the species. There was substantial gene flow between the eastern and western An. minimus populations without detection of significant gene flow barriers.

Partial indoor residual spraying with pirimiphos-methyl as an effective and cost-saving measure for the control of Anopheles gambiae s.l. in northern Ghana

The scale up of indoor residual spraying (IRS) and insecticide treated nets have contributed significantly to global reductions in malaria prevalence over the last two decades. However, widespread pyrethroid resistance has necessitated the use of new and more expensive insecticides for IRS. Partial IRS with pirimiphos-methyl in experimental huts and houses in a village-wide trial was evaluated against Anopheles gambiae s.l. in northern Ghana. Four different scenarios in which either only the top or bottom half of the walls of experimental huts were sprayed, with or without also spraying the ceiling were compared. Mortality of An. gambiae s.l. on partially sprayed walls was compared with the standard procedures in which all walls and ceiling surfaces are sprayed. A small-scale trial was then conducted to assess the effectiveness, feasibility, and cost of spraying only the upper walls and ceiling as compared to full IRS and no spraying in northern Ghana. Human landing catches were conducted to estimate entomological indices and determine the effectiveness of partial IRS. An established transmission dynamics model was parameterized by an analysis of the experimental hut data and used to predict the epidemiological impact and cost effectiveness of partial IRS for malaria control in northern Ghana. In the experimental huts, partial IRS of the top (IRR 0.89, p = 0.13) or bottom (IRR 0.90, p = 0.15) half of walls and the ceiling was not significantly less effective than full IRS in terms of mosquito mortality. In the village trial, the annual entomological inoculation rate was higher for the unsprayed control (217 infective bites/person/year (ib/p/yr)) compared with the fully and partially sprayed sites, with 28 and 38 ib/p/yr, respectively. The transmission model predicts that the efficacy of partial IRS against all-age prevalence of malaria after six months would be broadly equivalent to a full IRS campaign in which 40% reduction is expected relative to no spray campaign. At scale, partial IRS in northern Ghana would have resulted in a 33% cost savings ($496,426) that would enable spraying of 36,000 additional rooms. These findings suggest that partial IRS is an effective, feasible, and cost saving approach to IRS that could be adopted to sustain and expand implementation of this key malaria control intervention.

Effects of insemination and blood-feeding on locomotor activity of wild-derived females of the malaria mosquito Anopheles coluzzii

BACKGROUND

Behavioural shifts in the canonical location and timing of biting have been reported in natural populations of anopheline malaria vectors following the implementation of insecticide-based indoor vector control interventions. These modifications increase the likelihood of human-vector contact and allow mosquitoes to avoid insecticides, both conditions being favourable to residual transmission of the malarial parasites. The biting behaviour of mosquitoes follows rhythms that are under the control of biological clocks and environmental conditions, modulated by physiological states. In this work we explore modifications of spontaneous locomotor activity expressed by mosquitoes in different physiological states to highlight phenotypic variability associated to circadian control that may contribute to explain residual transmission in the field.

METHODS

The F10 generation progeny of field-collected Anopheles coluzzii from southwestern Burkina Faso was tested using an automated recording apparatus (Locomotor Activity Monitor, TriKinetics Inc.) under LD 12:12 or DD light regimens in laboratory-controlled conditions. Activity recordings of each test were carried out for a week with 6-day-old females belonging to four experimental treatments, representing factorial combinations of two physiological variables: insemination status (virgin vs inseminated) and gonotrophic status (glucose fed vs blood fed). Chronobiological features of rhythmicity in locomotor activity were explored using periodograms, diversity indices, and generalized linear mixed modelling.

RESULTS

The average strength of activity, onset of activity, and acrophase were modulated by both nutritional and insemination status as well as by the light regimen. Inseminated females showed a significant excess of arrhythmic activity under DD. When rhythmicity was observed in DD, females displayed sustained activity also during the subjective day.

CONCLUSIONS

Insemination and gonotrophic status influence the underlying light and circadian control of chronobiological features of locomotor activity. Overrepresentation of arrhythmic chronotypes as well as the sustained activity of inseminated females during the subjective day under DD conditions suggests potential activity of natural populations of A. coluzzii during daytime under dim conditions, with implications for residual transmission of malarial parasites.

Impact of cattle on the abundance of indoor and outdoor resting malaria vectors in southern Malawi

BACKGROUND

Understanding the blood feeding preferences and resting habits of malaria vectors is important for assessing and designing effective malaria vector control tools. The presence of livestock, such as cattle, which are used as blood meal hosts by some malaria vectors, may impact malaria parasite transmission dynamics. The presence of livestock may provide sufficient blood meals for the vectors, thereby reducing the frequency of vectors biting humans. Alternatively, the presence of cattle may enhance the availability of blood meals such that infectious mosquitoes may survive longer, thereby increasing the risk of malaria transmission. This study assessed the effect of household-level cattle presence and distribution on the abundance of indoor and outdoor resting malaria vectors.

METHODS

Houses with and without cattle were selected in Chikwawa district, southern Malawi for sampling resting malaria vectors. Prokopack aspirators and clay pots were used for indoor and outdoor sampling, respectively. Each house was sampled over two consecutive days. For houses with cattle nearby, the number of cattle and the distances from the house to where the cattle were corralled the previous night were recorded. All data were analysed using generalized linear models fitted with Poisson distribution.

RESULTS

The malaria vectors caught resting indoors were Anopheles gambiae sensu stricto (s.s.), Anopheles arabiensis and Anopheles funestus s.s. Outdoor collections consisted primarily of An. arabiensis. The catch sizes of indoor resting An. gambiae sensu lato (s.l.) were not different in houses with and without cattle (P = 0.34). The presence of cattle near a house was associated with a reduction in the abundance of indoor resting An. funestus s.l. (P = 0.04). This effect was strongest when cattle were kept overnight ≤ 15 m away from the houses (P = 0.03). The blood meal hosts varied across the species.

CONCLUSION

These results highlight differences between malaria vector species and their interactions with potential blood meal hosts, which may have implications for malaria risk. Whereas An. arabiensis remained unaffected, the reduction of An. funestus s.s. in houses near cattle suggests a potential protective effect of cattle. However, the low abundance of mosquitoes reduced the power of some analyses and limited the generalizability of the results to other settings. Therefore, further studies incorporating the vectors' host-seeking behaviour/human biting rates are recommended to fully support the primary finding.

Identification of new Anopheles gambiae transcriptional enhancers using a cross-species prediction approach

The success of transgenic mosquito vector control approaches relies on well-targeted gene expression, requiring the identification and characterization of a diverse set of mosquito promoters and transcriptional enhancers. However, few enhancers have been characterized in Anopheles gambiae to date. Here, we employ the SCRMshaw method we previously developed to predict enhancers in the A. gambiae genome, preferentially targeting vector-relevant tissues such as the salivary glands, midgut and nervous system. We demonstrate a high overall success rate, with at least 8 of 11 (73%) tested sequences validating as enhancers in an in vivo xenotransgenic assay. Four tested sequences drive expression in either the salivary gland or the midgut, making them directly useful for probing the biology of these infection-relevant tissues. The success of our study suggests that computational enhancer prediction should serve as an effective means for identifying A. gambiae enhancers with activity in tissues involved in malaria propagation and transmission.

Combating mosquito-borne diseases using genetic control technologies

Mosquito-borne diseases, such as dengue and malaria, pose significant global health burdens. Unfortunately, current control methods based on insecticides and environmental maintenance have fallen short of eliminating the disease burden. Scalable, deployable, genetic-based solutions are sought to reduce the transmission risk of these diseases. Pathogen-blocking Wolbachia bacteria, or genome engineering-based mosquito control strategies including gene drives have been developed to address these problems, both requiring the release of modified mosquitoes into the environment. Here, we review the latest developments, notable similarities, and critical distinctions between these promising technologies and discuss their future applications for mosquito-borne disease control.

Species Composition, Parous Rate, and Infection Rate of Anopheles Mosquitoes (Diptera: Culicidae) in Bahir Dar City Administration, Northwest Ethiopia

Anopheles mosquitoes are the main vectors of malaria. There is little information on the current entomological aspects of Anopheles mosquitoes in Amhara region of northwestern Ethiopia. Therefore, the aim of this study was to assess the prevailing species composition, parous rate, and infection rate of Anopheles mosquitoes in the Bahir Dar city administration. A community-based cross-sectional study was conducted from January through July 2020. For this, six Centers for Disease Control and Prevention light traps (three traps indoor and three traps outdoor) were used to collect adult female Anopheles mosquitoes. The species were morphologically identified, and the parous and infection rates were determined via dissection of ovaries and salivary gland, respectively. A total of 378 adult female Anopheles mosquitoes comprised of three species (Anopheles d'thali, Anopheles rhodesiensis, and Anopheles gambiae complex) were collected and identified at the study sites. Anopheles rhodesiensis was the predominant species accounting for 90% of all collections at the Zenzelima site, followed by An. gambiae complex (6.5%). In contrast, An. gambiae complex was the predominant species at the Tis Abay site, comprising 94% of captures. The overall parous and infection rates were 35 (62.5%) and 1 (2.9%), respectively.

Aptamers isolated against mosquito-borne pathogens

Mosquito-borne diseases are a major threat to public health. The shortcomings of diagnostic tools, especially those that are antibody-based, have been blamed in part for the rising annual morbidity and mortality caused by these diseases. Antibodies harbor a number of disadvantages that can be clearly addressed by aptamers as the more promising molecular recognition elements. Aptamers are defined as single-stranded DNA or RNA oligonucleotides generated by SELEX that exhibit high binding affinity and specificity against a wide variety of target molecules based on their unique structural conformations. A number of aptamers were developed against mosquito-borne pathogens such as Dengue virus, Zika virus, Chikungunya virus, Plasmodium parasite, Francisella tularensis, Japanese encephalitis virus, Venezuelan equine encephalitis virus, Rift Valley fever virus and Yellow fever virus. Intrigued by these achievements, we carry out a comprehensive overview of the aptamers developed against these mosquito-borne infectious agents. Characteristics of the aptamers and their roles in diagnostic, therapeutic as well as other applications are emphasized.

The private life of malaria parasites: Strategies for sexual reproduction

Malaria parasites exhibit a complex lifecycle, requiring extensive asexual replication in the liver and blood of the vertebrate host, and in the haemocoel of the insect vector. Yet, they must also undergo a single round of sexual reproduction, which occurs in the vector's midgut upon uptake of a blood meal. Sexual reproduction is obligate for infection of the vector and thus, is essential for onwards transmission to new hosts. Sex in malaria parasites involves several bottlenecks in parasite number, making the stages involved attractive targets for blocking disease transmission. Malaria parasites have evolved a suite of adaptations ("strategies") to maximise the success of sexual reproduction and transmission, which could undermine transmission-blocking interventions. Yet, understanding parasite strategies may also reveal novel opportunities for such interventions. Here, we outline how evolutionary and ecological theories, developed to explain reproductive strategies in multicellular taxa, can be applied to explain two reproductive strategies (conversion rate and sex ratio) expressed by malaria parasites within the vertebrate host.

Ammonium transporter AcAmt mutagenesis uncovers reproductive and physiological defects without impacting olfactory responses to ammonia in the malaria vector mosquito Anopheles coluzzii

Anopheline mosquitoes are the sole vectors of malaria and rely on olfactory cues for host seeking in which ammonia derived from human sweat plays an essential role. To investigate the function of the Anopheles coluzzii ammonium transporter (AcAmt) in the mosquito olfactory system, we generated an AcAmt null mutant line using CRISPR/Cas9. AcAmt^-/- mutants displayed a series of novel phenotypes compared with wild-type mosquitoes including significantly lower insemination rates during mating and increased mortality during eclosion. Furthermore, AcAmt^-/- males showed significantly lower sugar consumption while AcAmt^-/- females and pupae displayed significantly higher ammonia levels than their wild-type counterparts. Surprisingly, in contrast to previous studies in Drosophila that revealed that the mutation of the ammonium transporter (DmAmt) induces a dramatic reduction of ammonia responses in antennal coeloconic sensilla, no significant differences were observed across a range of peripheral sensory neuron responses to ammonia and other odorants between wild-type and AcAmt^-/- females. These data support the existence in mosquitoes of novel compensatory ammonia-sensing mechanisms that are likely to have evolved as a result of the importance of ammonia in host-seeking and other behaviors.

Ivermectin treatment in humans for reducing malaria transmission

BACKGROUND

Malaria is transmitted through the bite of Plasmodium-infected adult female Anopheles mosquitoes. Ivermectin, an anti-parasitic drug, acts by killing mosquitoes that are exposed to the drug while feeding on the blood of people (known as blood feeds) who have ingested the drug. This effect on mosquitoes has been demonstrated by individual randomized trials. This effect has generated interest in using ivermectin as a tool for malaria control.

OBJECTIVES

To assess the effect of community administration of ivermectin on malaria transmission.

SEARCH METHODS

We searched the Cochrane Infectious Diseases Group (CIDG) Specialized Register, CENTRAL, MEDLINE, Embase, LILACS, Science Citation index - expanded, the World Health Organization (WHO) International Clinical Trials Registry Platform, ClinicalTrials.gov, and the National Institutes of Health (NIH) RePORTER database to 14 January 2021. We checked the reference lists of included studies for other potentially relevant studies, and contacted researchers working in the field for unpublished and ongoing trials.

SELECTION CRITERIA

We included cluster-randomized controlled trials (cRCTs) that compared ivermectin, as single or multiple doses, with a control treatment or placebo given to populations living in malaria-endemic areas, in the context of mass drug administration. Primary outcomes were prevalence of malaria parasite infection and incidence of clinical malaria in the community.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data on the number of events and the number of participants in each trial arm at the time of assessment. For rate data, we noted the total time at risk in each trial arm. To assess risk of bias, we used Cochrane's RoB 2 tool for cRCTs. We documented the method of data analysis, any adjustments for clustering or other covariates, and recorded the estimate of the intra-cluster correlation (ICC) coefficient. We re-analysed the trial data provided by the trial authors to adjust for cluster effects. We used a Poisson mixed-effect model with small sample size correction, and a cluster-level analysis using the linear weighted model to adequately adjust for clustering.  MAIN RESULTS: We included one cRCT and identified six ongoing trials.  The included cRCT examined the incidence of malaria in eight villages in Burkina Faso, randomized to two arms. Both trial arms received a single dose of ivermectin 150 µg/kg to 200 µg/kg, together with a dose of albendazole. The villages in the intervention arm received an additional five doses of ivermectin, once every three weeks. Children were enrolled into an active cohort, in which they were repeatedly screened for malaria infection.  The primary outcome was the cumulative incidence of uncomplicated malaria in a cohort of children aged five years and younger, over the 18-week study. We judged the study to be at high risk of bias, as the analysis did not account for clustering or correlation between participants in the same village. The study did not demonstrate an effect of Ivermectin on the cumulative incidence of uncomplicated malaria in the cohort of children over the 18-week study (risk ratio 0.86, 95% confidence interval (CI) 0.62 to 1.17; P = 0.2607; very low-certainty evidence).

AUTHORS' CONCLUSIONS

We are uncertain whether community administration of ivermectin has an effect on malaria transmission, based on one trial published to date.

Influence of insecticide resistance on the biting and resting preferences of malaria vectors in the Gambia

Background

The scale-up of indoor residual spraying and long-lasting insecticidal nets, together with other interventions have considerably reduced the malaria burden in The Gambia. This study examined the biting and resting preferences of the local insecticide-resistant vector populations few years following scale-up of anti-vector interventions.

Method

Indoor and outdoor-resting Anopheles gambiae mosquitoes were collected between July and October 2019 from ten villages in five regions in The Gambia using pyrethrum spray collection (indoor) and prokopack aspirator from pit traps (outdoor). Polymerase chain reaction assays were performed to identify molecular species, insecticide resistance mutations, Plasmodium infection rate and host blood meal.

Results

A total of 844 mosquitoes were collected both indoors (421, 49.9%) and outdoors (423, 50.1%). Four main vector species were identified, including An. arabiensis (indoor: 15%, outdoor: 26%); An. coluzzii (indoor: 19%, outdoor: 6%), An. gambiae s.s. (indoor: 11%, outdoor: 16%), An. melas (indoor: 2%, outdoor: 0.1%) and hybrids of An. coluzzii-An. gambiae s.s (indoors: 3%, outdoors: 2%). A significant preference for outdoor resting was observed in An. arabiensis (Pearson X² = 22.7, df = 4, P<0.001) and for indoor resting in An. coluzzii (Pearson X² = 55.0, df = 4, P<0.001). Prevalence of the voltage-gated sodium channel (Vgsc)-1014S was significantly higher in the indoor-resting (allele freq. = 0.96, 95%CI: 0.78–1, P = 0.03) than outdoor-resting (allele freq. = 0.82, 95%CI: 0.76–0.87) An. arabiensis population. For An. coluzzii, the prevalence of most mutation markers was higher in the outdoor (allele freq. = 0.92, 95%CI: 0.81–0.98) than indoor-resting (allele freq. = 0.78, 95%CI: 0.56–0.86) mosquitoes. However, in An. gambiae s.s., the prevalence of Vgsc-1014F, Vgsc-1575Y and GSTe2-114T was high (allele freq. = 0.96–1), but did not vary by resting location. The overall sporozoite positivity rate was 1.3% (95% CI: 0.5–2%) in mosquito populations. Indoor-resting An. coluzzii had mainly fed on human blood while indoor-resting An. arabiensis fed on animal blood.

Conclusion

In this study, high levels of resistance mutations were observed that could be influencing the mosquito populations to rest indoors or outdoors. The prevalent animal-biting behaviour demonstrated in the mosquito populations suggest that larval source management could be an intervention to complement vector control in this setting.

Intragenomic sequence variations in the second internal transcribed spacer (ITS2) ribosomal DNA of the malaria vector Anopheles stephensi

Second Internal Transcribed Spacer (ITS2) ribosomal DNA (rDNA) sequence is a widely used molecular marker for species-identification or -delimitation due to observed concerted evolution which is believed to homogenize rDNA copies in an interbreeding population. However, intra-specific differences in ITS2 of Anopheles stephensi have been reported. This study reports the presence of intragenomic sequence variation in the ITS2-rDNA of An. stephensi and hypothesizes that observed intra-specific differences in this species may have resulted due to ambiguous DNA sequence-chromatogram resulting from intragenomic heterogeneity. Anopheles stephensi collected from different parts of India were sequenced for complete ITS2 and the variable region of 28S-rDNA (d1-d3 domains). Intragenomic variations were found in ITS2 region of all An. stephensi sequenced, but no such variation was observed in d1 to d3 domains of 28S-rDNA. Cloning and sequencing of ITS2 through the d3 domain of the 28S region of rDNA from representative samples from northern, central, and southern India confirmed the presence of intragenomic variation in ITS2 due to transitions at three loci and two bp indel in a di-nucleotide microsatellite locus. Multiple haplotypes were observed in ITS2 raised from such variations. Due to the absence of detectable intragenomic sequence variation in the d1 to d3 domain of 28S rDNA of An. stephensi, this region can serve as an ideal reference sequence for taxonomic and phylogenetic studies. The presence of intragenomic variation in rDNA should be carefully examined before using this as a molecular marker for species delimitation or phylogenetic analyses.

Environmental and spatial risk factors for the larval habitats of Plasmodium knowlesi vectors in Sabah, Malaysian Borneo

Land-use changes, such as deforestation and agriculture, can influence mosquito vector populations and malaria transmission. These land-use changes have been linked to increased incidence in human cases of the zoonotic malaria Plasmodium knowlesi in Sabah, Malaysian Borneo. This study investigates whether these associations are partially driven by fine-scale land-use changes creating more favourable aquatic breeding habitats for P. knowlesi anopheline vectors. Using aerial remote sensing data, we developed a sampling frame representative of all land use types within a major focus of P. knowlesi transmission. From 2015 to 2016 monthly longitudinal surveys of larval habitats were collected in randomly selected areas stratified by land use type. Additional remote sensing data on environmental variables, land cover and landscape configuration were assembled for the study site. Risk factor analyses were performed over multiple spatial scales to determine associations between environmental and spatial variables and anopheline larval presence. Habitat fragmentation (300 m), aspect (350 m), distance to rubber plantations (100 m) and Culex larval presence were identified as risk factors for Anopheles breeding. Additionally, models were fit to determine the presence of potential larval habitats within the areas surveyed and used to generate a time-series of monthly predictive maps. These results indicate that land-use change and topography influence the suitability of larval habitats, and may partially explain the link between P. knowlesi incidence and deforestation. The predictive maps, and identification of the spatial scales at which risk factors are most influential may aid spatio-temporally targeted vector control interventions.

Compensatory mechanisms in resistant Anopheles gambiae AcerKis and KdrKis neurons modulate insecticide-based mosquito control

In the malaria vector Anopheles gambiae, two point mutations in the acetylcholinesterase (ace-1R) and the sodium channel (kdrR) genes confer resistance to organophosphate/carbamate and pyrethroid insecticides, respectively. The mechanisms of compensation that recover the functional alterations associated with these mutations and their role in the modulation of insecticide efficacy are unknown. Using multidisciplinary approaches adapted to neurons isolated from resistant Anopheles gambiae AcerKis and KdrKis strains together with larval bioassays, we demonstrate that nAChRs, and the intracellular calcium concentration represent the key components of an adaptation strategy ensuring neuronal functions maintenance. In AcerKis neurons, the increased effect of acetylcholine related to the reduced acetylcholinesterase activity is compensated by expressing higher density of nAChRs permeable to calcium. In KdrKis neurons, changes in the biophysical properties of the L1014F mutant sodium channel, leading to enhance overlap between activation and inactivation relationships, diminish the resting membrane potential and reduce the fraction of calcium channels available involved in acetylcholine release. Together with the lower intracellular basal calcium concentration observed, these factors increase nAChRs sensitivity to maintain the effect of low concentration of acetylcholine. These results explain the opposite effects of the insecticide clothianidin observed in AcerKis and KdrKis neurons in vitro and in vivo.

Diversity and natural selection of Merozoite surface Protein-1 in three species of human malaria parasites: Contribution from South-East Asian isolates

The present study aimed to examine the genetic diversity of human malaria parasites (i.e., P. falciparum, P. vivax and P. knowlesi) in Malaysia and southern Thailand targeting the 19-kDa C-terminal region of Merozoite Surface Protein-1 (MSP-1₁₉). This region is essential for the recognition and invasion of erythrocytes and it is considered one of the leading candidates for asexual blood stage vaccines. However, the genetic data of MSP-1₁₉ among human malaria parasites in Malaysia is limited and there is also a need to update the current sequence diversity of this gene region among the Thailand isolates. In this study, genomic DNA was extracted from 384 microscopy-positive blood samples collected from patients who attended the hospitals or clinics in Malaysia and malaria clinics in Thailand from the year 2008 to 2016. The MSP-1₁₉ was amplified using PCR followed by bidirectional sequencing. DNA sequences identified in the present study were subjected to Median-joining network analysis with sequences of MSP-1₁₉ obtained from GenBank. DNA sequence analysis revealed that PfMSP-1₁₉ of Malaysian and Thailand isolates was not genetically conserved as high number of haplotypes were detected and positive selection was prevalent in PfMSP-1₁₉, hence questioning its suitability to be used as a vaccine candidate. A novel haplotype (Q/TNG/L) was also detected in Thailand P. falciparum isolate. In contrast, PvMSP-1₁₉ was highly conserved, however for the first time, a non-synonymous substitution (A1657S) was reported among Malaysian isolates. As for PkMSP-1₁₉, the presence of purifying selection and low nucleotide diversity indicated that it might be a potential vaccine target for P. knowlesi.