The AWED trial (Applying Wolbachia to Eliminate Dengue) to assess the efficacy of Wolbachia-infected mosquito deployments to reduce dengue incidence in Yogyakarta, Indonesia: study protocol for a cluster randomised controlled trial

Proceedings of the 7th Asia Dengue Summit, June 2024

Background: The 7th Asia Dengue Summit (ADS), titled "Road Map to Zero Dengue Death", was held in Malaysia from 5 to 7 June 2024. The summit was co-organized by Asia Dengue Voice and Action (ADVA); Global Dengue and Aedes-Transmitted Diseases Consortium (GDAC); Southeast Asian Ministers of Education Tropical Medicine and Public Health Network (SEAMEO TROPMED); Fondation Mérieux (FMx); and the International Society for Neglected Tropical Diseases (ISNTD). Objectives: Dengue experts from academia and research, as well as representatives from the Ministries of Health, Regional and Global World Health Organization (WHO), and International Vaccine Institute (IVI), came together to highlight the crucial need for an integrated approach for dengue control and achieve the target of zero dengue deaths. Methods: With more than 50 speakers and delegates from over 28 countries, twelve symposiums, and three full days, the 7th ADS highlighted approaches to curb the growing danger of dengue. The summit included topics ranging from emerging dengue trends, insights from dengue human infection models, the immunology of dengue, and vaccine updates to antivirals and host-directed therapeutics. Conclusions: The 7th Asia Dengue Summit reinforced the importance of an integrated, collaborative approach to dengue prevention and control. By bringing together diverse stakeholders and launching innovative initiatives such as the Dengue Slayers Challenge, the summit advanced the regional and global agenda to achieve zero dengue deaths. The exchange of knowledge and strategies at the summit is expected to contribute significantly to improved dengue management and community engagement in affected regions.

A Double Machine Learning Approach for the Evaluation of COVID-19 Vaccine Effectiveness Under the Test-Negative Design: Analysis of Québec Administrative Data

The test-negative design (TND), which is routinely used for monitoring seasonal flu vaccine effectiveness (VE), has recently become integral to COVID-19 vaccine surveillance, notably in Québec, Canada. Some studies have addressed the identifiability and estimation of causal parameters under the TND, but efficiency bounds for nonparametric estimators of the target parameter under the unconfoundedness assumption have not yet been investigated. Motivated by the goal of improving adjustment for measured confounders when estimating COVID-19 VE among community-dwelling people aged≥ 60 $$ \ge 60 $$ years in Québec, we propose a one-step doubly robust and locally efficient estimator called TNDDR (TND doubly robust), which utilizes cross-fitting (sample splitting) and can incorporate machine learning techniques to estimate the nuisance functions and thus improve control for measured confounders. We derive the efficient influence function (EIF) for the marginal expectation of the outcome under a vaccination intervention, explore the von Mises expansion, and establish the conditions forn $$ \sqrt{n} $$ -consistency, asymptotic normality, and double robustness of TNDDR. The proposed estimator is supported by both theoretical and empirical justifications.

Symbiotic Bacteria: Wolbachia, Midgut Microbiota in Mosquitoes and Their Importance for Vector Prevention Strategies

Mosquito-borne illnesses pose a significant threat to eradication under existing vector management measures. Chemo-based vector control strategies (use of insecticides) raise a complication of resistance and environmental pollution. Biological control methods are an alternative approach to overcoming this complication arising from insecticides. The mosquito gut microbiome is essential to supporting the factors that involve metabolic regulation and metamorphic development (from juvenile to adult), as well as the induction of an immune response. The induced immune response includes the JAK-STAT, IMD, and Toll pathways due to the microbial interaction with the midgut cells (MG cells) that prevent disease transmission to humans. The aforementioned sequel to the review provides information about endosymbiont Wolbachia, which contaminates insect cells, including germline and somatic cytoplasm, and inhibits disease-causing pathogen development and transmission by competing for resources within the cell. Moreover, it reduces the host population via cytoplasmic incompatibility (CI), feminization, male killing, and parthenogenesis. Furthermore, the Cif factor in Wolbachia is responsible for CI induction that produces inviable cells with the translocating systems and the embryonic defect-causing protein factor, WalE1 (WD0830), which manipulates the host actin. This potential of Wolbachia can be used to design a paratransgenic system to control vectors in the field. An extracellular symbiotic bacterium such as Asaia, which is grown in the growth medium, is used to transfer lethal genes within itself. Besides, the genetically transferred symbiotic bacteria infect the wild mosquito population and are easily manifold. So, it might be suitable for vector control strategies in the future.

Dengue virus genomic surveillance in the applying Wolbachia to eliminate dengue trial reveals genotypic efficacy and disruption of focal transmission

Release of Aedes aegypti mosquitoes infected with Wolbachia pipientis (wMel strain) is a biocontrol approach against Ae. aegypti-transmitted arboviruses. The Applying Wolbachia to Eliminate Dengue (AWED) cluster-randomised trial was conducted in Yogyakarta, Indonesia in 2018-2020 and provided pivotal evidence for the efficacy of wMel-Ae. aegypti mosquito population replacement in significantly reducing the incidence of virologically-confirmed dengue (VCD) across all four dengue virus (DENV) serotypes. Here, we sequenced the DENV genomes from 318 dengue cases detected in the AWED trial, with the aim of characterising DENV genetic diversity, measuring genotype-specific intervention effects, and inferring DENV transmission dynamics in wMel-treated and untreated areas of Yogyakarta. Phylogenomic analysis of all DENV sequences revealed the co-circulation of five endemic DENV genotypes: DENV-1 genotype I (12.5%) and IV (4.7%), DENV-2 Cosmopolitan (47%), DENV-3 genotype I (8.5%), and DENV-4 genotype II (25.7%), and one recently imported genotype, DENV-4 genotype I (1.6%). The diversity of genotypes detected among AWED trial participants enabled estimation of the genotype-specific protective efficacies of wMel, which were similar (± 10%) to the point estimates of the respective serotype-specific efficacies reported previously. This indicates that wMel afforded protection to all of the six genotypes detected in Yogyakarta. We show that within this substantial overall viral diversity, there was a strong spatial and temporal structure to the DENV genomic relationships, consistent with highly focal DENV transmission around the home in wMel-untreated areas and a near-total disruption of transmission by wMel. These findings can inform long-term monitoring of DENV transmission dynamics in Wolbachia-treated areas including Yogyakarta.

Exploring Iguape Virus-A Lesser-Known Orthoflavivirus

Brazil has earned the moniker "arbovirus hotspot", providing an ideal breeding ground for a multitude of arboviruses thriving in various zoonotic and urban cycles. As the planet warms and vectors expand their habitat range, a nuanced understanding of lesser-known arboviruses and the factors that could drive their emergence becomes imperative. Among these viruses is the Iguape virus (IGUV), a member of the Orthoflavivirus aroaense species, which was first isolated in 1979 from a sentinel mouse in the municipality of Iguape, within the Vale do Ribeira region of São Paulo State. While evidence suggests that IGUV circulates among birds, wild rodents, marsupials, bats, and domestic birds, there is no information available on its pathogenesis in both humans and animals. The existing literature on IGUV spans decades, is outdated, and is often challenging to access. In this review, we have curated information from the known literature, clarifying its elusive nature and investigating the factors that may influence its emergence. As an orthoflavivirus, IGUV poses a potential threat, which demands our attention and vigilance, considering the serious outbreaks that the Zika virus, another neglected orthoflavivirus, has unleashed in the recent past.

Wolbachia-carrying Aedes mosquitoes for preventing dengue infection

BACKGROUND

Dengue is a global health problem of high significance, with 3.9 billion people at risk of infection. The geographic expansion of dengue virus (DENV) infection has resulted in increased frequency and severity of the disease, and the number of deaths has increased in recent years. Wolbachia,an intracellular bacterial endosymbiont, has been under investigation for several years as a novel dengue-control strategy. Some dengue vectors (Aedes mosquitoes) can be transinfected with specific strains of Wolbachia, which decreases their fitness (ability to survive and mate) and their ability to reproduce, inhibiting the replication of dengue. Both laboratory and field studies have demonstrated the potential effect of Wolbachia deployments on reducing dengue transmission, and modelling studies have suggested that this may be a self-sustaining strategy for dengue prevention, although long-term effects are yet to be elucidated.

OBJECTIVES

To assess the efficacy of Wolbachia-carrying Aedes speciesdeployments (specifically wMel-, wMelPop-, and wAlbB- strains of Wolbachia) for preventing dengue virus infection.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, four other databases, and two trial registries up to 24 January 2024.

SELECTION CRITERIA

Randomized controlled trials (RCTs), including cluster-randomized controlled trials (cRCTs), conducted in dengue endemic or epidemic-prone settings were eligible. We sought studies that investigated the impact of Wolbachia-carrying Aedes deployments on epidemiological or entomological dengue-related outcomes, utilizing either the population replacement or population suppression strategy.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected eligible studies, extracted data, and assessed the risk of bias using the Cochrane RoB 2 tool. We used odds ratios (OR) with the corresponding 95% confidence intervals (CI) as the effect measure for dichotomous outcomes. For count/rate outcomes, we planned to use the rate ratio with 95% CI as the effect measure. We used adjusted measures of effect for cRCTs. We assessed the certainty of evidence using GRADE.

MAIN RESULTS

One completed cRCT met our inclusion criteria, and we identified two further ongoing cRCTs. The included trial was conducted in an urban setting in Yogyakarta, Indonesia. It utilized a nested test-negative study design, whereby all participants aged three to 45 years who presented at healthcare centres with a fever were enrolled in the study provided they had resided in the study area for the previous 10 nights. The trial showed that wMel-Wolbachia infected Ae aegypti deployments probably reduce the odds of contracting virologically confirmed dengue by 77% (OR 0.23, 95% CI 0.15 to 0.35; 1 trial, 6306 participants; moderate-certainty evidence). The cluster-level prevalence of wMel Wolbachia-carrying mosquitoes remained high over two years in the intervention arm of the trial, reported as 95.8% (interquartile range 91.5 to 97.8) across 27 months in clusters receiving wMel-Wolbachia Ae aegypti deployments, but there were no reliable comparative data for this outcome. Other primary outcomes were the incidence of virologically confirmed dengue, the prevalence of dengue ribonucleic acid in the mosquito population, and mosquito density, but there were no data for these outcomes. Additionally, there were no data on adverse events.

AUTHORS' CONCLUSIONS

The included trial demonstrates the potential significant impact of wMel-Wolbachia-carrying Ae aegypti mosquitoes on preventing dengue infection in an endemic setting, and supports evidence reported in non-randomized and uncontrolled studies. Further trials across a greater diversity of settings are required to confirm whether these findings apply to other locations and country settings, and greater reporting of acceptability and cost are important.

Procedures for the Detection of Wolbachia-Conferred Antiviral Protection in Drosophila melanogaster

Spread of Wolbachia infections in host populations may be enhanced by Wolbachia-conferred protection from viral pathogens. Wolbachia-infected Drosophila melanogaster survive the pathogenic effects of positive-sense single-stranded RNA virus infections at a higher rate than the flies without Wolbachia. The protection can occur with or without detectable reduction in virus titer. For the comparisons to be meaningful, Wolbachia-harboring and Wolbachia-free insects need to be genetically matched, and original populations of gut microbiota need to be restored after the removal of Wolbachia using antibiotics. Here, I describe the procedures needed to detect Wolbachia-conferred antiviral protection against Drosophila C virus measured as the difference in survival and viral titer between flies with and without Wolbachia.

Impact of randomised wmel Wolbachia deployments on notified dengue cases and insecticide fogging for dengue control in Yogyakarta City

BACKGROUND

Releases of Wolbachia (wMel)-infected Aedes aegypti mosquitoes significantly reduced the incidence of virologically confirmed dengue in a previous cluster randomised trial in Yogyakarta City, Indonesia. Following the trial, wMel releases were extended to the untreated control areas, to achieve city-wide coverage of Wolbachia.

OBJECTIVE

In this predefined analysis, we evaluated the impact of the wMel deployments in Yogyakarta on dengue hemorrhagic fever (DHF) case notifications and on the frequency of perifocal insecticide spraying by public health teams.

METHODS

Monthly counts of DHF cases notified to the Yogyakarta District Health Office between January 2006 and May 2022 were modelled as a function of time-varying local wMel treatment status (fully- and partially-treated vs untreated, and by quintile of wMel prevalence). The frequency of insecticide fogging in wMel-treated and untreated areas was analysed using negative binomial regression.

RESULTS

Notified DHF incidence was 83% lower in fully treated vs untreated periods (IRR 0.17 [95% CI 0.14, 0.20]), and 78% lower in areas with 80-100% wMel prevalence compared to areas with 0-20% wMel (IRR 0.23 [0.17, 0.30]). A similar intervention effect was observed at 60-80% wMel prevalence as at 80-100% prevalence (76% vs 78% efficacy, respectively). Pre-intervention, insecticide fogging occurred at similar frequencies in areas later randomised to wMel-treated and untreated arms of the trial. After wMel deployment, fogging occurred significantly less frequently in treated areas (IRR 0.17 [0.10, 0.30]).

CONCLUSIONS

Deployments of wMel-infected Aedes aegypti mosquitoes resulted in an 83% reduction in the application of perifocal insecticide spraying, consistent with lower dengue case notifications in wMel-treated areas. These results show that the Wolbachia intervention effect demonstrated previously in a cluster randomised trial was also measurable from routine surveillance data.

Effects of cattle on vector-borne disease risk to humans: A systematic review

Vector-borne pathogens (VBPs) causing vector-borne diseases (VBDs) can circulate among humans, domestic animals, and wildlife, with cattle in particular serving as an important source of exposure risk to humans. The close associations between humans and cattle can facilitate the transmission of numerous VBPs, impacting public health and economic security. Published studies demonstrate that cattle can influence human exposure risk positively, negatively, or have no effect. There is a critical need to synthesize the information in the scientific literature on this subject, in order to illuminate the various ecological mechanisms that can affect VBP exposure risk in humans. Therefore, the aim of this systematic review was to review the scientific literature, provide a synthesis of the possible effects of cattle on VBP risk to humans, and propose future directions for research. This study was performed according to the PRISMA 2020 extension guidelines for systematic review. After screening 470 peer-reviewed articles published between 1999-2019 using the databases Web of Science Core Collection, PubMed Central, CABI Global Health, and Google Scholar, and utilizing forward and backward search techniques, we identified 127 papers that met inclusion criteria. Results of the systematic review indicate that cattle can be beneficial or harmful to human health with respect to VBDs depending on vector and pathogen ecology and livestock management practices. Cattle can increase risk of exposure to infections spread by tsetse flies and ticks, followed by sandflies and mosquitoes, through a variety of mechanisms. However, cattle can have a protective effect when the vector prefers to feed on cattle instead of humans and when chemical control measures (e.g., acaricides/insecticides), semio-chemicals, and other integrated vector control measures are utilized in the community. We highlight that further research is needed to determine ways in which these mechanisms may be exploited to reduce VBD risk in humans.

Quantifying the impact of Wolbachia releases on dengue infection in Townsville, Australia

From October 2014 to February 2019, local authorities in Townsville, North Queensland, Australia continually introduced Wolbachia-infected mosquitoes to control seasonal outbreaks of dengue infection. In this study, we develop a mathematical modelling framework to estimate the effectiveness of this intervention as well as the relative dengue transmission rates of Wolbachia-infected and wild-type mosquitoes. We find that the transmission rate of Wolbachia-infected mosquitoes is reduced approximately by a factor of 20 relative to the uninfected wild-type population. In addition, the Townsville Wolbachia release program led to a 65% reduction in predicted dengue incidence during the release period and over 95% reduction in the 24 months that followed. Finally, to investigate the potential impact of other Wolbachia release programs, we use our estimates of relative transmissibility to calculate the relationship between the reproductive number of dengue and the proportion of Wolbachia-infected mosquitoes in the vector population.

Does ignoring transmission dynamics lead to underestimation of the impact of interventions against mosquito-borne disease?

New vector-control technologies to fight mosquito-borne diseases are urgently needed, the adoption of which depends on efficacy estimates from large-scale cluster-randomised trials (CRTs). The release of Wolbachia-infected mosquitoes is one promising strategy to curb dengue virus (DENV) transmission, and a recent CRT reported impressive reductions in dengue incidence following the release of these mosquitoes. Such trials can be affected by multiple sources of bias, however. We used mathematical models of DENV transmission during a CRT of Wolbachia-infected mosquitoes to explore three such biases: human movement, mosquito movement and coupled transmission dynamics between trial arms. We show that failure to account for each of these biases would lead to underestimated efficacy, and that the majority of this underestimation is due to a heretofore unrecognised bias caused by transmission coupling. Taken together, our findings suggest that Wolbachia-infected mosquitoes could be even more promising than the recent CRT suggested. By emphasising the importance of accounting for transmission coupling between arms, which requires a mathematical model, we highlight the key role that models can play in interpreting and extrapolating the results from trials of vector control interventions.

Double Negative Control Inference in Test-Negative Design Studies of Vaccine Effectiveness

The test-negative design (TND) has become a standard approach to evaluate vaccine effectiveness against the risk of acquiring infectious diseases in real-world settings, such as Influenza, Rotavirus, Dengue fever, and more recently COVID-19. In a TND study, individuals who experience symptoms and seek care are recruited and tested for the infectious disease which defines cases and controls. Despite TND's potential to reduce unobserved differences, in healthcare seeking behavior (HSB) between vaccinated and unvaccinated subjects, it remains subject to various potential biases. First, residual confounding may remain due to unobserved HSB occupation as healthcare worker, or previous infection history. Second, because selection into the TND sample is a common consequence of infection and HSB, collider stratification bias may exist when conditioning the analysis on tested samples, which further induces confounding by latent HSB. In this paper, we present a novel approach to identify and estimate vaccine effectiveness in the target population by carefully leveraging a pair of negative control exposure and outcome variables to account for potential hidden bias in TND studies. We illustrate our proposed method with extensive simulations and an application to study COVID-19 vaccine effectiveness using data from the University of Michigan Health System.

Double Negative Control Inference in Test-Negative Design Studies of Vaccine Effectiveness

The test-negative design (TND) has become a standard approach to evaluate vaccine effectiveness against the risk of acquiring infectious diseases in real-world settings, such as Influenza, Rotavirus, Dengue fever, and more recently COVID-19. In a TND study, individuals who experience symptoms and seek care are recruited and tested for the infectious disease which defines cases and controls. Despite TND's potential to reduce unobserved differences in healthcare seeking behavior (HSB) between vaccinated and unvaccinated subjects, it remains subject to various potential biases. First, residual confounding bias may remain due to unobserved HSB, occupation as healthcare worker, or previous infection history. Second, because selection into the TND sample is a common consequence of infection and HSB, collider stratification bias may exist when conditioning the analysis on testing, which further induces confounding by latent HSB. In this paper, we present a novel approach to identify and estimate vaccine effectiveness in the target population by carefully leveraging a pair of negative control exposure and outcome variables to account for potential hidden bias in TND studies. We illustrate our proposed method with extensive simulation and an application to study COVID-19 vaccine effectiveness using data from the University of Michigan Health System.

Assessing the efficacy of male Wolbachia-infected mosquito deployments to reduce dengue incidence in Singapore: study protocol for a cluster-randomized controlled trial

BACKGROUND

Dengue is a severe environmental public health challenge in tropical and subtropical regions. In Singapore, decreasing seroprevalence and herd immunity due to successful vector control has paradoxically led to increased transmission potential of the dengue virus. We have previously demonstrated that incompatible insect technique coupled with sterile insect technique (IIT-SIT), which involves the release of X-ray-irradiated male Wolbachia-infected mosquitoes, reduced the Aedes aegypti population by 98% and dengue incidence by 88%. This novel vector control tool is expected to be able to complement current vector control to mitigate the increasing threat of dengue on a larger scale. We propose a multi-site protocol to study the efficacy of IIT-SIT at reducing dengue incidence.

METHODS/DESIGN

The study is designed as a parallel, two-arm, non-blinded cluster-randomized (CR) controlled trial to be conducted in high-rise public housing estates in Singapore, an equatorial city-state. The aim is to determine whether large-scale deployment of male Wolbachia-infected Ae. aegypti mosquitoes can significantly reduce dengue incidence in intervention clusters. We will use the CR design, with the study area comprising 15 clusters with a total area of 10.9 km2, covering approximately 722,204 residents in 1713 apartment blocks. Eight clusters will be randomly selected to receive the intervention, while the other seven will serve as non-intervention clusters. Intervention efficacy will be estimated through two primary endpoints: (1) odds ratio of Wolbachia exposure distribution (i.e., probability of living in an intervention cluster) among laboratory-confirmed reported dengue cases compared to test-negative controls and (2) laboratory-confirmed reported dengue counts normalized by population size in intervention versus non-intervention clusters.

DISCUSSION

This study will provide evidence from a multi-site, randomized controlled trial for the efficacy of IIT-SIT in reducing dengue incidence. The trial will provide valuable information to estimate intervention efficacy for this novel vector control approach and guide plans for integration into national vector control programs in dengue-endemic settings.

TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT05505682 . Registered on 16 August 2022. Retrospectively registered.

Exploring Conditions for Handling Packing and Shipping Aedes aegypti Males to Support an SIT Field Project in Brazil

The sterile insect technique (SIT) application, as an alternative tool for conventional mosquito control methods, has recently gained prominence. Nevertheless, some SIT components require further development, such as protocols under large-scale conditions, focusing on packing and shipping mosquitoes, and considering transporting time. Immobilization of Aedes aegypti males was tested at temperatures 4, 7, 10, and 14 °C, and each temperature was assessed for 60, 90, and 120 min. The recovery after 24 h was also studied. Chilled and control-reared males had comparable survival rates for all conditions, although 4 °C for 120 min impacted male survival. The male escape rate was affected after 60 min of exposure at 4 °C; this difference was not significant, with 24 h of recovery. First, we defined the successful immobilization at 4 °C for 60 min, thus enabling the evaluation of two transportation intervals: 6 and 24 h, with the assessment of different compaction densities of 100 and 150 mosquitoes/cm³ at 10 °C to optimize the shipment. Compaction during simulated mosquito shipments reduced survival rates significantly after 6 and 24 h. In the mating propensity and insemination experiments, the sterile males managed to inseminate 40 to 66% for all treatments in laboratory conditions. The male insemination propensity was affected only by the highest compaction condition concerning the control. The analysis of the densities (100 and 150 males/cm³) showed that a higher density combined with an extended shipment period (24 h) negatively impacted the percentage of inseminated females. The results are very helpful in developing and improving the SIT packing and shipment protocols. Further studies are required to evaluate all combined parameters' synergetic effects that can combine irradiation to assess sexual competitiveness when sterile males are released into the field.

Dengue virus population genetics in Yogyakarta, Indonesia prior to city-wide Wolbachia deployment

Dengue has been endemic in Yogyakarta, Indonesia for decades. Here, we report the dengue epidemiology, entomology, and virology in Yogyakarta in 2016-2017, prior to the commencement of the Applying Wolbachia to Eliminate Dengue (AWED) randomized trial. Dengue epidemiological data were compiled and blood samples from dengue-suspected patients were tested for dengue virus (DENV). Ae. aegypti mosquito samples were caught from the field using BG-Sentinel traps and tested for the presence of DENV infection. Sequencing of the DENV E gene was used to determine the phylogeny and genotypes of circulating DENV. Within the last decade, the 2016-2017 dengue incidence was considered very high. Among the 649 plasma samples collected between March 2016-February 2017; and 36,910 mosquito samples collected between December 2016-May 2017, a total of 197 and 38 samples were DENV-positive by qRT-PCR, respectively. All four DENV serotypes were detected, with DENV-3 (n = 88; 44.67%) and DENV-1 (n = 87; 44.16%) as the predominant serotype, followed by DENV-4 (n = 12; 6.09%) and DENV-2 (n = 10; 5.08%). The Yogyakarta DENV-1 isolates were classified into Genotype I and IV, while DENV-2, DENV-3, and DENV-4 isolates were classified into the Cosmopolitan genotype, Genotype I, and Genotype II, respectively. Yogyakarta DENV isolates were closely related to Indonesian strains from neighboring Javanese cities, consistent with the endemic circulation of DENV on this highly populous island. Our study provides comprehensive baseline information on the DENV population genetic characteristics in Yogyakarta, which are useful as baseline data for the AWED trial and the future DENV surveillance in the city in the presence of a Wolbachia-infected Ae. aegypti population.

Aedes aegypti abundance and insecticide resistance profiles in the Applying Wolbachia to Eliminate Dengue trial

The Applying Wolbachia to Eliminate Dengue (AWED) trial was a parallel cluster randomised trial that demonstrated Wolbachia (wMel) introgression into Ae. aegypti populations reduced dengue incidence. In this predefined substudy, we compared between treatment arms, the relative abundance of Ae. aegypti and Ae. albopictus before, during and after wMel-introgression. Between March 2015 and March 2020, 60,084 BG trap collections yielded 478,254 Ae. aegypti and 17,623 Ae. albopictus. Between treatment arms there was no measurable difference in Ae. aegypti relative abundance before or after wMel-deployments, with a count ratio of 0.96 (95% CI 0.76, 1.21) and 1.00 (95% CI 0.85, 1.17) respectively. More Ae. aegypti were caught per trap per week in the wMel-intervention arm compared to the control arm during wMel deployments (count ratio 1.23 (95% CI 1.03, 1.46)). Between treatment arms there was no measurable difference in the Ae. albopictus population size before, during or after wMel-deployment (overall count ratio 1.10 (95% CI 0.89, 1.35)). We also compared insecticide resistance phenotypes of Ae. aegypti in the first and second years after wMel-deployments. Ae. aegypti field populations from wMel-treated and untreated arms were similarly resistant to malathion (0.8%), permethrin (1.25%) and cyfluthrin (0.15%) in year 1 and year 2 of the trial. In summary, we found no between-arm differences in the relative abundance of Ae. aegypti or Ae. albopictus prior to or after wMel introgression, and no between-arm difference in Ae. aegypti insecticide resistance phenotypes. These data suggest neither Aedes abundance, nor insecticide resistance, confounded the epidemiological outcomes of the AWED trial.

EVITA Dengue: a cluster-randomized controlled trial to EValuate the efficacy of Wolbachia-InfecTed Aedes aegypti mosquitoes in reducing the incidence of Arboviral infection in Brazil

BACKGROUND

Arboviruses transmitted by Aedes aegypti including dengue, Zika, and chikungunya are a major global health problem, with over 2.5 billion at risk for dengue alone. There are no licensed antivirals for these infections, and safe and effective vaccines are not yet widely available. Thus, prevention of arbovirus transmission by vector modification is a novel approach being pursued by multiple researchers. However, the field needs high-quality evidence derived from randomized, controlled trials upon which to base the implementation and maintenance of vector control programs. Here, we report the EVITA Dengue trial design (DMID 17-0111), which assesses the efficacy in decreasing arbovirus transmission of an innovative approach developed by the World Mosquito Program for vector modification of Aedes mosquitoes by Wolbachia pipientis.

METHODS

DMID 17-0111 is a cluster-randomized trial in Belo Horizonte, Brazil, with clusters defined by primary school catchment areas. Clusters (n = 58) will be randomized 1:1 to intervention (release of Wolbachia-infected Aedes aegypti mosquitoes) vs. control (no release). Standard vector control activities (i.e., insecticides and education campaigns for reduction of mosquito breeding sites) will continue as per current practice in the municipality. Participants (n = 3480, 60 per cluster) are children aged 6-11 years enrolled in the cluster-defining school and living within the cluster boundaries who will undergo annual serologic surveillance for arboviral infection. The primary objective is to compare sero-incidence of arboviral infection between arms.

DISCUSSION

DMID 17-0111 aims to determine the efficacy of Wolbachia-infected mosquito releases in reducing human infections by arboviruses transmitted by Aedes aegypti and will complement the mounting evidence for this method from large-scale field releases and ongoing trials. The trial also represents a critical step towards robustness and rigor for how vector control methods are assessed, including the simultaneous measurement and correlation of entomologic and epidemiologic outcomes. Data from this trial will inform further the development of novel vector control methods.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04514107 . Registered on 17 August 2020 Primary sponsor: National Institute of Health, National Institute of Allergy and Infectious Diseases.

Potential test-negative design study bias in outbreak settings: application to Ebola vaccination in Democratic Republic of Congo

BACKGROUND

Infectious disease outbreaks present unique challenges to study designs for vaccine evaluation. Test-negative design (TND) studies have previously been used to estimate vaccine effectiveness and have been proposed for Ebola virus disease (EVD) vaccines. However, there are key differences in how cases and controls are recruited during outbreaks and pandemics of novel pathogens, whcih have implications for the reliability of effectiveness estimates using this design.

METHODS

We use a modelling approach to quantify TND bias for a prophylactic vaccine under varying study and epidemiological scenarios. Our model accounts for heterogeneity in vaccine distribution and for two potential routes to testing and recruitment into the study: self-reporting and contact-tracing. We derive conventional and hybrid TND estimators for this model and suggest ways to translate public health response data into the parameters of the model.

RESULTS

Using a conventional TND study, our model finds biases in vaccine effectiveness estimates. Bias arises due to differential recruitment from self-reporting and contact-tracing, and due to clustering of vaccination. We estimate the degree of bias when recruitment route is not available, and propose a study design to eliminate the bias if recruitment route is recorded.

CONCLUSIONS

Hybrid TND studies can resolve the design bias with conventional TND studies applied to outbreak and pandemic response testing data, if those efforts collect individuals' routes to testing. Without route to testing, other epidemiological data will be required to estimate the magnitude of potential bias in a conventional TND study. Since these studies may need to be conducted retrospectively, public health responses should obtain these data, and generic protocols for outbreak and pandemic response studies should emphasize the need to record routes to testing.

Whitefly endosymbionts: IPM opportunity or tilting at windmills?

Whiteflies are sap-sucking insects responsible for high economic losses. They colonize hundreds of plant species and cause direct feeding damage and indirect damage through transmission of devastating viruses. Modern agriculture has seen a history of invasive whitefly species and populations that expand to novel regions, bringing along fierce viruses. Control efforts are hindered by fast virus transmission, insecticide-resistant populations, and a wide host range which permits large natural reservoirs for whiteflies. Augmentative biocontrol by parasitoids while effective in suppressing high population densities in greenhouses falls short when it comes to preventing virus transmission and is ineffective in the open field. A potential source of much needed novel control strategies lays within a diverse community of whitefly endosymbionts. The idea to exploit endosymbionts for whitefly control is as old as identification of these bacteria, yet it still has not come to fruition. We review where our knowledge stands on the aspects of whitefly endosymbiont evolution, biology, metabolism, multitrophic interactions, and population dynamics. We show how these insights are bringing us closer to the goal of better integrated pest management strategies. Combining most up to date understanding of whitefly-endosymbiont interactions and recent technological advances, we discuss possibilities of disrupting and manipulating whitefly endosymbionts, as well as using them for pest control.

Designing effective Wolbachia release programs for mosquito and arbovirus control

Mosquitoes carrying endosymbiotic bacteria called Wolbachia are being released in mosquito and arbovirus control programs around the world through two main approaches: population suppression and population replacement. Open field releases of Wolbachia-infected male mosquitoes have achieved over 95% population suppression by reducing the fertility of wild mosquito populations. The replacement of populations with Wolbachia-infected females is self-sustaining and can greatly reduce local dengue transmission by reducing the vector competence of mosquito populations. Despite many successful interventions, significant questions and challenges lie ahead. Wolbachia, viruses and their mosquito hosts can evolve, leading to uncertainty around the long-term effectiveness of a given Wolbachia strain, while few ecological impacts of Wolbachia releases have been explored. Wolbachia strains are diverse and the choice of strain to release should be made carefully, taking environmental conditions and the release objective into account. Mosquito quality control, thoughtful community awareness programs and long-term monitoring of populations are essential for all types of Wolbachia intervention. Releases of Wolbachia-infected mosquitoes show great promise, but existing control measures remain an important way to reduce the burden of mosquito-borne disease.

Case-area targeted interventions (CATI) for reactive dengue control: Modelling effectiveness of vector control and prophylactic drugs in Singapore

BACKGROUND

Targeting interventions to areas that have recently experienced cases of disease is one strategy to contain outbreaks of infectious disease. Such case-area targeted interventions (CATI) have become an increasingly popular approach for dengue control but there is little evidence to suggest how precisely targeted or how recent cases need to be, to mount an effective response. The growing interest in the development of prophylactic and therapeutic drugs for dengue has also given new relevance for CATI strategies to interrupt transmission or deliver early treatment.

METHODS/PRINCIPAL FINDINGS

Here we develop a patch-based mathematical model of spatial dengue spread and fit it to spatiotemporal datasets from Singapore. Simulations from this model suggest CATI strategies could be effective, particularly if used in lower density areas. To maximise effectiveness, increasing the size of the radius around an index case should be prioritised even if it results in delays in the intervention being applied. This is partially because large intervention radii ensure individuals receive multiple and regular rounds of drug dosing or vector control, and thus boost overall coverage. Given equivalent efficacy, CATIs using prophylactic drugs are predicted to be more effective than adult mosquito-killing vector control methods and may even offer the possibility of interrupting individual chains of transmission if rapidly deployed. CATI strategies quickly lose their effectiveness if baseline transmission increases or case detection rates fall.

CONCLUSIONS/SIGNIFICANCE

These results suggest CATI strategies can play an important role in dengue control but are likely to be most relevant for low transmission areas where high coverage of other non-reactive interventions already exists. Controlled field trials are needed to assess the field efficacy and practical constraints of large operational CATI strategies.

Nanobased Platforms for Diagnosis and Treatment of COVID-19: From Benchtop to Bedside

Human respiratory viral infections are the leading cause of morbidity and mortality around the world. Among the various respiratory viruses, coronaviruses (e.g., SARS-CoV-2) have created the greatest challenge and most frightening health threat worldwide. Human coronaviruses typically infect the upper respiratory tract, causing illnesses that range from common cold-like symptoms to severe acute respiratory infections. Several promising vaccine formulations have become available since the beginning of 2021. Nevertheless, achievement of herd immunity is still far from being realized. Social distancing remains the only effective measure against SARS-CoV-2 infection. Nanobiotechnology enables the design of nanobiosensors. These nanomedical diagnostic devices have opened new vistas for early detection of viral infections. The present review outlines recent research on the effectiveness of nanoplatforms as diagnostic and antiviral tools against coronaviruses. The biological properties of coronavirus and infected host organs are discussed. The challenges and limitations encountered in combating SARS-CoV-2 are highlighted. Potential nanodevices such as nanosensors, nanobased vaccines, and smart nanomedicines are subsequently presented for combating current and future mutated versions of coronaviruses.

Efficacy of Wolbachia-Infected Mosquito Deployments for the Control of Dengue

BACKGROUND

Aedes aegypti mosquitoes infected with the wMel strain of Wolbachia pipientis are less susceptible than wild-type A. aegypti to dengue virus infection.

METHODS

We conducted a cluster-randomized trial involving releases of wMel-infected A. aegypti mosquitoes for the control of dengue in Yogyakarta, Indonesia. We randomly assigned 12 geographic clusters to receive deployments of wMel-infected A. aegypti (intervention clusters) and 12 clusters to receive no deployments (control clusters). All clusters practiced local mosquito-control measures as usual. A test-negative design was used to assess the efficacy of the intervention. Patients with acute undifferentiated fever who presented to local primary care clinics and were 3 to 45 years of age were recruited. Laboratory testing was used to identify participants who had virologically confirmed dengue (VCD) and those who were test-negative controls. The primary end point was symptomatic VCD of any severity caused by any dengue virus serotype.

RESULTS

After successful introgression of wMel into the intervention clusters, 8144 participants were enrolled; 3721 lived in intervention clusters, and 4423 lived in control clusters. In the intention-to-treat analysis, VCD occurred in 67 of 2905 participants (2.3%) in the intervention clusters and in 318 of 3401 (9.4%) in the control clusters (aggregate odds ratio for VCD, 0.23; 95% confidence interval [CI], 0.15 to 0.35; P = 0.004). The protective efficacy of the intervention was 77.1% (95% CI, 65.3 to 84.9) and was similar against the four dengue virus serotypes. The incidence of hospitalization for VCD was lower among participants who lived in intervention clusters (13 of 2905 participants [0.4%]) than among those who lived in control clusters (102 of 3401 [3.0%]) (protective efficacy, 86.2%; 95% CI, 66.2 to 94.3).

CONCLUSIONS

Introgression of wMel into A. aegypti populations was effective in reducing the incidence of symptomatic dengue and resulted in fewer hospitalizations for dengue among the participants. (Funded by the Tahija Foundation and others; AWED ClinicalTrials.gov number, NCT03055585; Indonesia Registry number, INA-A7OB6TW.).

Genome engineering in insects for the control of vector borne diseases

Insects cause many vector-borne infectious diseases and have become a major threat to human health. Although many control measures are undertaken, some insects are resistant to it, exacerbated by environmental changes which is a major challenge for control measures. Genetic studies by targeting the genomes of insects may offer an alternative strategy. Developments with novel genome engineering technologies have stretched our ability to target and modify any genomic sequence in Eukaryotes including insects. Genome engineering tools such as zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and most recently discovered, clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) systems hold the potential to control the vector-borne diseases. In this chapter, we review the vector control strategy undertaken by employing three major genome engineering tools (ZFNs, TALENs, and CRISPR/Cas9) and discuss the future prospects of this system to control insect vectors. Finally, we also discuss the CRISPR-based gene drive system and its concerns due to ecological impacts.

Cost of Dengue Illness in Indonesia across Hospital, Ambulatory, and not Medically Attended Settings

Informed decisions concerning emerging technologies against dengue require knowledge about the disease’s economic cost and each stakeholder’s potential benefits from better control. To generate such data for Indonesia, we reviewed recent literature, analyzed expenditure and utilization data from two hospitals and two primary care facilities in Yogyakarta city, and interviewed 67 dengue patients from hospital, ambulatory, and not medically attended settings. We derived the cost of a dengue episode by outcome, setting, and the breakdown by payer. We then calculated aggregate Yogyakarta and national costs and 95% uncertainty intervals (95% UIs). Dengue costs per nonfatal case in hospital, ambulatory, not medically attended, and overall average settings were US$316.24 (95% UI: $242.30–$390.18), US$22.45 (95% UI: $14.12–$30.77), US$7.48 (95% UI: $2.36–$12.60), and US$50.41 (95% UI: $35.75–$65.07), respectively. Costs of nonfatal episodes were borne by the patient’s household (37%), social contributors (relatives and friends, 20%), national health insurance (25%), and other sources (government, charity, and private insurance, 18%). After including fatal cases, the average cost per episode became $90.41 (95% UI: $72.79–$112.35). Indonesia had an estimated 7.535 (95% UI: 1.319–16.513) million dengue episodes in 2017, giving national aggregate costs of $681.26 (95% UI: $232.28–$2,371.56) million. Unlike most previous research that examined only the formal medical sector, this study included the estimated 63% of national dengue episodes that were not medically attended. Also, this study used actual costs, rather than charges, which generally understate dengue’s economic burden in public facilities. Overall, this study found that Indonesia’s aggregate cost of dengue was 73% higher than previously estimated, strengthening the need for effective control.

Wolbachia: A tool for livestock ectoparasite control

Ectoparasites and livestock-associated insects are a major concern throughout the world because of their economic and welfare impacts. Effective control is challenging and relies mainly on the use of chemical insecticides and acaricides. Wolbachia, an arthropod and nematode-infecting, maternally-transmitted endosymbiont is currently of widespread interest for use in novel strategies for the control of a range of arthropod-vectored human diseases and plant pests but to date has received only limited consideration for use in the control of diseases of veterinary concern. Here, we review the currently available information on Wolbachia in veterinary ectoparasites and disease vectors, consider the feasibility for use of Wolbachia in the control of livestock pests and diseases and highlight critical issues which need further investigation.

Modulation of acyl-carnitines, the broad mechanism behind Wolbachia-mediated inhibition of medically important flaviviruses in Aedes aegypti

Wolbachia-infected mosquitoes are refractory to flavivirus infections, but the role of lipids in Wolbachia-mediated virus blocking remains to be elucidated. Here, we use liquid chromatography mass spectrometry to provide a comprehensive picture of the lipidome of Aedes aegypti (Aag2) cells infected with Wolbachia only, either dengue or Zika virus only, and Wolbachia-infected Aag2 cells superinfected with either dengue or Zika virus. This approach identifies a class of lipids, acyl-carnitines, as being down-regulated during Wolbachia infection. Furthermore, treatment with an acyl-carnitine inhibitor assigns a crucial role for acyl-carnitines in the replication of dengue and Zika viruses. In contrast, depletion of acyl-carnitines increases Wolbachia density while addition of commercially available acyl-carnitines impairs Wolbachia production. Finally, we show an increase in flavivirus infection of Wolbachia-infected cells with the addition of acyl-carnitines. This study uncovers a previously unknown role for acyl-carnitines in this tripartite interaction that suggests an important and broad mechanism that underpins Wolbachia-mediated pathogen blocking.

Dengue and Zika Viruses: Epidemiological History, Potential Therapies, and Promising Vaccines

Dengue virus (DENV), which can lead to fatal hemorrhagic fever, affects 390 million people worldwide. The closely related Zika virus (ZIKV) causes microcephaly in newborns and Guillain-Barré syndrome in adults. Both viruses are mostly transmitted by Aedes albopictus and Aedes aegypti mosquitoes, which, due to globalization of trade and travel alongside climate change, are spreading worldwide, paving the way to DENV and ZIKV transmission and the occurrence of new epidemics. Local outbreaks have already occurred in temperate climates, even in Europe. As there are no specific treatments, these viruses are an international public health concern. Here, we analyze and discuss DENV and ZIKV outbreaks history, clinical and pathogenesis features, and modes of transmission, supplementing with information on advances on potential therapies and restraining measures. Taking advantage of the knowledge of the structure and biological function of the capsid (C) protein, a relatively conserved protein among flaviviruses, within a genus that includes DENV and ZIKV, we designed and patented a new drug lead, pep14-23 (WO2008/028939A1). It was demonstrated that it inhibits the interaction of DENV C protein with the host lipid system, a process essential for viral replication. Such an approach can be used to develop new therapies for related viruses, such as ZIKV.

Long-Term Mosquito culture with SkitoSnack, an artificial blood meal replacement

The reliance on blood is a limiting factor for mass rearing of mosquitoes for Sterile-Insect-Technique (SIT) and other mosquito-based control strategies. To solve this problem, we have developed SkitoSnack, a formulated diet for Aedes aegypti (L) mosquitoes, as an alternative for vertebrate blood. Here we addressed the question if long-term yellow fever mosquito culture with SkitoSnack resulted in changed life history traits and fitness of the offspring compared to blood-raised mosquitoes. We also explored if SkitoSnack is suitable to raise Asian tiger mosquitos, Aedes albopictus (L.), and the human bed bug, Cimex lectularius (L). We measured life history traits for 30th generation SkitoSnack-raised Ae. aegypti and 11th generation SkitoSnack-raised Ae. albopictus, and compared them with control mosquitoes raised on blood only. We compared meal preference, flight performance, and reproductive fitness in Ae. aegypti raised on SkitoSnack or blood. We also offered SkitoSnack to bed bug nymphs. We found that long-term culture with SkitoSnack resulted in mosquitoes with similar life history traits compared to bovine blood-raised mosquitoes in both species we studied. Also, Ae. aegypti mosquitoes raised on SkitoSnack had similar flight performance compared to blood raised mosquitoes, were still strongly attracted by human smell and had equal mating success. Minimal feeding occurred in bed bugs. Our results suggest that long-term culture with the blood-meal replacement SkitoSnack results in healthy, fit mosquitoes. Therefore, artificial diets like SkitoSnack can be considered as a viable alternative for vertebrate blood in laboratory mosquito culture as well as for mosquito mass production for Sterile-Insect-Technique mosquito control interventions. SkitoSnack was not suitable to induce engorgement of bed bugs.

Immunopathology and immunotherapeutic strategies in severe acute respiratory syndrome coronavirus 2 infection

The outbreak of coronavirus disease 2019 (COVID-19) and pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has become a major concern globally. As of 14 April 2020, more than 1.9 million COVID-19 cases have been reported in 185 countries. Some patients with COVID-19 develop severe clinical manifestations, while others show mild symptoms, suggesting that dysregulation of the host immune response contributes to disease progression and severity. In this review, we have summarized and discussed recent immunological studies focusing on the response of the host immune system and the immunopathology of SARS-CoV-2 infection as well as immunotherapeutic strategies for COVID-19. Immune evasion by SARS-CoV-2, functional exhaustion of lymphocytes, and cytokine storm have been discussed as part of immunopathology mechanisms in SARS-CoV-2 infection. Some potential immunotherapeutic strategies to control the progression of COVID-19, such as passive antibody therapy and use of interferon αβ and IL-6 receptor (IL-6R) inhibitor, have also been discussed. This may help us to understand the immune status of patients with COVID-19, particularly those with severe clinical presentation, and form a basis for further immunotherapeutic investigations.

JNK pathway restricts DENV2, ZIKV and CHIKV infection by activating complement and apoptosis in mosquito salivary glands

Arbovirus infection of Aedes aegypti salivary glands (SGs) determines transmission. However, there is a dearth of knowledge on SG immunity. Here, we characterized SG immune response to dengue, Zika and chikungunya viruses using high-throughput transcriptomics. We also describe a transcriptomic response associated to apoptosis, blood-feeding and lipid metabolism. The three viruses differentially regulate components of Toll, Immune deficiency (IMD) and c-Jun N- terminal Kinase (JNK) pathways. However, silencing of the Toll and IMD pathway components showed variable effects on SG infection by each virus. In contrast, regulation of the JNK pathway produced consistent responses in both SGs and midgut. Infection by the three viruses increased with depletion of the activator Kayak and decreased with depletion of the negative regulator Puckered. Virus-induced JNK pathway regulates the complement factor, Thioester containing protein-20 (TEP20), and the apoptosis activator, Dronc, in SGs. Individual and co-silencing of these genes demonstrate their antiviral effects and that both may function together. Co-silencing either TEP20 or Dronc with Puckered annihilates JNK pathway antiviral effect. Upon infection in SGs, TEP20 induces antimicrobial peptides (AMPs), while Dronc is required for apoptosis independently of TEP20. In conclusion, we revealed the broad antiviral function of JNK pathway in SGs and showed that it is mediated by a TEP20 complement and Dronc-induced apoptosis response. These results expand our understanding of the immune arsenal that blocks arbovirus transmission.

Arboviral diseases caused by dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV) viruses are responsible for large number of death and debilitation around the world. These viruses are transmitted to humans by the mosquito vector, Aedes aegypti. During the bites, infected salivary glands (SGs) release saliva containing viruses, which initiate human infection. As the tissue where transmitted viruses are produced, SG infection is a key determinant of transmission. To bridge the knowledge gap in vector-virus molecular interactions in SGs, we describe the transcriptome after DENV, ZIKV and CHIKV infection using RNA-sequencing and characterized the immune response in this tissue. Our study reveals the broad antiviral function of c-Jun N-terminal kinase (JNK) pathway against DENV, ZIKV and CHIKV in SGs. We further show that it is mediated by the complement system and apoptosis, identifying the mechanism. Our study adds the JNK pathway to the immune arsenal that can be harnessed to engineer refractory vectors.

The cost-effectiveness of controlling dengue in Indonesia using wMel Wolbachia released at scale: a modelling study

BACKGROUND

Release of virus-blocking Wolbachia-infected mosquitoes is an emerging disease control strategy that aims to control dengue and other arboviral infections. Early entomological data and modelling analyses have suggested promising outcomes, and wMel Wolbachia releases are now ongoing or planned in 12 countries. To help inform government, donor, or philanthropist decisions on scale-up beyond single city releases, we assessed this technology's cost-effectiveness under alternative programmatic options.

METHODS

Using costing data from existing Wolbachia releases, previous dynamic model-based estimates of Wolbachia effectiveness, and a spatially explicit model of release and surveillance requirements, we predicted the costs and effectiveness of the ongoing programme in Yogyakarta City and three new hypothetical programmes in Yogyakarta Special Autonomous Region, Jakarta, and Bali.

RESULTS

We predicted Wolbachia to be a highly cost-effective intervention when deployed in high-density urban areas with gross cost-effectiveness below $1500 per DALY averted. When offsets from the health system and societal perspective were included, such programmes even became cost saving over 10-year time horizons with favourable benefit-cost ratios of 1.35 to 3.40. Sequencing Wolbachia releases over 10 years could reduce programme costs by approximately 38% compared to simultaneous releases everywhere, but also delays the benefits. Even if unexpected challenges occurred during deployment, such as emergence of resistance in the medium-term or low effective coverage, Wolbachia would remain a cost-saving intervention.

CONCLUSIONS

Wolbachia releases in high-density urban areas are expected to be highly cost-effective and could potentially be the first cost-saving intervention for dengue. Sites with strong public health infrastructure, fiscal capacity, and community support should be prioritised.

Cost-Effectiveness of Dengue Vaccination in Indonesia: Considering Integrated Programs with Wolbachia-Infected Mosquitos and Health Education

Despite the fact that morbidity and mortality rates due to dengue infection in Indonesia are relatively high, a dengue vaccination has not yet been introduced. Next to vaccination, Wolbachia-infected mosquitoes and health education have been considered to be potential interventions to prevent dengue infection in Indonesia. This study was aimed to analyse the cost-effectiveness of dengue vaccination in Indonesia whilst taking Wolbachia and health education programs into account. An age-structured decision tree model was developed to assess the cost-effectiveness. Approximately 4,701,100 children were followed-up in a 10-year time horizon within a 1-year analytical cycle. We compared three vaccination strategies: one focussing on vaccination only, another combining vaccination and a Wolbachia program, and a third scenario combining vaccination and health education. All scenarios were compared with a no-intervention strategy. The result showed that only vaccination would reduce dengue fever (DF), dengue haemorrhagic fever (DHF), and dengue shock syndrome (DSS) by 123,203; 97,140 and 283 cases, respectively. It would save treatment cost at $10.3 million and $6.2 million from the healthcare and payer perspectives, respectively. The combination of vaccination and a Wolbachia program would reduce DF, DHF and DSS by 292,488; 230,541; and 672 cases, respectively. It would also save treatment cost at $24.3 million and $14.6 million from the healthcare and payer perspectives, respectively. The combination of vaccination and health education would reduce DF, DHF, and DSS by 187,986; 148,220; and 432 cases, respectively. It would save treatment cost at $15.6 million and $9.4 million from the healthcare and payer perspectives, respectively. The incremental cost-effectiveness ratios (ICERs) from the healthcare perspective were estimated to be $9995, $4460, and $6399 per quality-adjusted life year (QALY) gained for the respective scenarios. ICERs from the payer perspective were slightly higher. It can be concluded that vaccination combined with a Wolbachia program was confirmed to be the most cost-effective intervention. Dengue infection rate, vaccine efficacy, cost of Wolbachia program, underreporting factor for hospitalization, vaccine price and mortality rate were considered to be the most influential parameters affecting the ICERs.

Transinfection of buffalo flies (Haematobia irritans exigua) with Wolbachia and effect on host biology

BACKGROUND

Buffalo flies (Haematobia irritans exigua) (BF) and closely related horn flies (Haematobia irritans irritans) (HF) are invasive haematophagous parasites with significant economic and welfare impacts on cattle production. Wolbachia are intracellular bacteria found widely in insects and currently of much interest for use in novel strategies for the area wide control of insect pests and insect-vectored diseases. In this paper, we report the transinfection of BF towards the development of area-wide controls.

METHODS

Three stages of BF; embryos, pupae and adult female flies, were injected with different Wolbachia strains (wAlbB, wMel and wMelPop). The success of transinfection and infection dynamics was compared by real-time PCR and FISH and fitness effects were assessed in transinfected flies.

RESULTS

BF eggs were not easily injected because of their tough outer chorion and embryos were frequently damaged with less than 1% hatch rate of microinjected eggs. No Wolbachia infection was recorded in flies successfully reared from injected eggs. Adult and pupal injection resulted in higher survival rates and somatic and germinal tissue infections, with transmission to the succeeding generations on some occasions. Investigations of infection dynamics in flies from injected pupae confirmed that Wolbachia were actively multiplying in somatic tissues. Ovarian infections were confirmed with wMel and wMelPop in a number of instances, though not with wAlbB. Measurement of fitness traits indicated reduced longevity, decreased and delayed adult emergence, and reduced fecundity in Wolbachia-infected flies compared to mock-injected flies. Effects varied with the Wolbachia strain injected with most marked changes seen in the wMelPop-injected flies and least severe effects seen with wAlbB.

CONCLUSIONS

Adult and pupal injection were the most suitable methods for transinfecting BF and all three strains of Wolbachia successfully replicated in somatic tissues. The Wolbachia-induced fitness effects seen in transinfected BF suggest potential for use of the wMel or wMelPop strains in Wolbachia-based biocontrol programmes for BF.

Update to the AWED (Applying Wolbachia to Eliminate Dengue) trial study protocol: a cluster randomised controlled trial in Yogyakarta, Indonesia

BACKGROUND

The AWED (Applying Wolbachia to Eliminate Dengue) trial is a parallel, two-arm, non-blinded cluster randomised controlled trial that is under way in Yogyakarta, Indonesia, with the aim of measuring the efficacy of Wolbachia-infected Aedes aegypti deployments in reducing dengue incidence in an endemic setting. Enrolment began in January 2018 and is ongoing. The original study protocol was published in April 2018. Here, we describe amendments that have been made to the study protocol since commencement of the trial.

METHODS

The key protocol amendments are (1) a revised study duration with planned end of participant enrolment in August 2020, (2) the addition of new secondary objectives (i) to estimate serotype-specific efficacy of the Wolbachia intervention and (ii) to compare Ae. aegypti abundance in intervention versus untreated clusters, (3) an additional exposure classification for the per-protocol analysis where the Wolbachia exposure index is calculated using only the cluster-level Wolbachia prevalence in the participant's cluster of residence, (4) power re-estimation using a multinomial sampling method that better accounts for randomness in sampling, and (5) the addition of two trial stopping rules to address the potential for persistently low rates of virologically confirmed dengue case enrolment and Wolbachia contamination into untreated clusters. Additional minor changes to the protocol are also described.

DISCUSSION

The findings from this study will provide the first experimental evidence for the efficacy of Wolbachia in reducing dengue incidence. Enrolment in the trial will conclude this year (2020) and results will be reported shortly thereafter.

TRIAL REGISTRATION

ClinicalTrials.gov, identifier: NCT03055585. Registered on 14 February 2017. Last updated 22 March 2020.

Reduced dengue incidence following deployments of Wolbachia-infected Aedes aegypti in Yogyakarta, Indonesia: a quasi-experimental trial using controlled interrupted time series analysis

Background: Ae. aegypti mosquitoes stably transfected with the intracellular bacterium Wolbachia pipientis ( wMel strain) have been deployed for biocontrol of dengue and related arboviral diseases in multiple countries. Field releases in northern Australia have previously demonstrated near elimination of local dengue transmission from Wolbachia-treated communities, and pilot studies in Indonesia have demonstrated the feasibility and acceptability of the method. We conducted a quasi-experimental trial to evaluate the impact of scaled Wolbachia releases on dengue incidence in an endemic setting in Indonesia. Methods: In Yogyakarta City, Indonesia, following extensive community engagement, wMel Wolbachia-carrying mosquitoes were released every two weeks for 13-15 rounds over seven months in 2016-17, in a contiguous 5 km 2 area (population 65,000). A 3 km 2 area (population 34,000) on the opposite side of the city was selected a priori as an untreated control area. Passive surveillance data on notified hospitalised dengue patients was used to evaluate the epidemiological impact of Wolbachia deployments, using controlled interrupted time-series analysis. Results: Rapid and sustained introgression of wMel Wolbachia into local Ae. aegypti populations was achieved. Thirty-four dengue cases were notified from the intervention area and 53 from the control area (incidence 26 vs 79 per 100,000 person-years) during 24 months following Wolbachia deployment. This corresponded in the regression model to a 73% reduction in dengue incidence (95% confidence interval 49%,86%) associated with the Wolbachia intervention. Exploratory analysis including 6 months additional post-intervention observations showed a small strengthening of this effect (30 vs 115 per 100,000 person-years; 76% reduction in incidence, 95%CI 60%,86%). Conclusions: We demonstrate a significant reduction in dengue incidence following successful introgression of Wolbachia into local Ae. aegypti populations in an endemic setting in Indonesia. These findings are consistent with previous field trials in northern Australia, and support the effectiveness of this novel approach for dengue control.

The continued threat of emerging flaviviruses

Flaviviruses are vector-borne RNA viruses that can emerge unexpectedly in human populations and cause a spectrum of potentially severe diseases including hepatitis, vascular shock syndrome, encephalitis, acute flaccid paralysis, congenital abnormalities and fetal death. This epidemiological pattern has occurred numerous times during the last 70 years, including epidemics of dengue virus and West Nile virus, and the most recent explosive epidemic of Zika virus in the Americas. Flaviviruses are now globally distributed and infect up to 400 million people annually. Of significant concern, outbreaks of other less well-characterized flaviviruses have been reported in humans and animals in different regions of the world. The potential for these viruses to sustain epidemic transmission among humans is poorly understood. In this Review, we discuss the basic biology of flaviviruses, their infectious cycles, the diseases they cause and underlying host immune responses to infection. We describe flaviviruses that represent an established ongoing threat to global health and those that have recently emerged in new populations to cause significant disease. We also provide examples of lesser-known flaviviruses that circulate in restricted areas of the world but have the potential to emerge more broadly in human populations. Finally, we discuss how an understanding of the epidemiology, biology, structure and immunity of flaviviruses can inform the rapid development of countermeasures to treat or prevent human infections as they emerge.

Arboviruses: A global public health threat

A conference on «ARBOVIRUSES, A GLOBAL PUBLIC HEALTH THREAT» was organized on June 20–22, 2018 at the Merieux Foundation Conference Center in Veyrier du Lac, France, to review and raise awareness to the global public health threat of epidemic arboviruses, and to advance the discussion on the control and prevention of arboviral diseases. The presentations by scientists and public health officials from Asia, the Americas, Europe and Africa strengthened the notion that arboviral diseases of both humans and domestic animals are progressively becoming dominant public health problems in the world. The repeated occurrence of recent deadly epidemics strongly reinforces the call for action against these viral diseases, and the need for developing effective vaccines, drugs, vector control tools and strong prevention programs.

Analysis of counts for cluster randomized trials: Negative controls and test-negative designs

In cluster randomized trials (CRTs), the outcome of interest is often a count at the cluster level. This occurs, for example, in evaluating an intervention with the outcome being the number of infections of a disease such as HIV or dengue or the number of hospitalizations in the cluster. Standard practice analyzes these counts through cluster outcome rates using an appropriate denominator (eg, population size). However, such denominators are sometimes unknown, particularly when the counts depend on a passive community surveillance system. We consider direct comparison of the counts without knowledge of denominators, relying on randomization to balance denominators. We also focus on permutation tests to allow for small numbers of randomized clusters. However, such approaches are subject to bias when there is differential ascertainment of counts across arms, a situation that may occur in CRTs that cannot implement blinded interventions. We suggest the use of negative control counts as a method to remove, or reduce, this bias, discussing the key properties necessary for an effective negative control. A current example of such a design is the recent extension of test-negative designs to CRTs testing community-level interventions. Via simulation, we compare the performance of new and standard estimators based on CRTs with negative controls to approaches that only use the original counts. When there is no differential ascertainment by intervention arm, the count-only approaches perform comparably to those using debiasing negative controls. However, under even modest differential ascertainment, the count-only estimators are no longer reliable.

The Global Expansion of Dengue: How Aedes aegypti Mosquitoes Enabled the First Pandemic Arbovirus

Dengue is an emerging viral disease principally transmitted by the Aedes (Stegomyia) aegypti mosquito. It is one of the fastest-growing global infectious diseases, with 100-400 million new infections a year, and is now entrenched in a growing number of tropical megacities. Behind this rapid rise is the simple adaptation of Ae. aegypti to a new entomological niche carved out by human habitation. This review describes the expansion of dengue and explores how key changes in the ecology of Ae. aegypti allowed it to become a successful invasive species and highly efficient disease vector. We argue that characterizing geographic heterogeneity in mosquito bionomics will be a key research priority that will enable us to better understand future dengue risk and design control strategies to reverse its global spread.

The importance of vector control for the control and elimination of vector-borne diseases

Vector-borne diseases (VBDs) such as malaria, dengue, and leishmaniasis exert a huge burden of morbidity and mortality worldwide, particularly affecting the poorest of the poor. The principal method by which these diseases are controlled is through vector control, which has a long and distinguished history. Vector control, to a greater extent than drugs or vaccines, has been responsible for shrinking the map of many VBDs. Here, we describe the history of vector control programmes worldwide from the late 1800s to date. Pre 1940, vector control relied on a thorough understanding of vector ecology and epidemiology, and implementation of environmental management tailored to the ecology and behaviour of local vector species. This complex understanding was replaced by a simplified dependency on a handful of insecticide-based tools, particularly for malaria control, without an adequate understanding of entomology and epidemiology and without proper monitoring and evaluation. With the rising threat from insecticide-resistant vectors, global environmental change, and the need to incorporate more vector control interventions to eliminate these diseases, we advocate for continued investment in evidence-based vector control. There is a need to return to vector control approaches based on a thorough knowledge of the determinants of pathogen transmission, which utilise a range of insecticide and non-insecticide-based approaches in a locally tailored manner for more effective and sustainable vector control.

Gene drive: progress and prospects

Gene drive is a naturally occurring phenomenon in which selfish genetic elements manipulate gametogenesis and reproduction to increase their own transmission to the next generation. Currently, there is great excitement about the potential of harnessing such systems to control major pest and vector populations. If synthetic gene drive systems can be constructed and applied to key species, they may be able to rapidly spread either modifying or eliminating the targeted populations. This approach has been lauded as a revolutionary and efficient mechanism to control insect-borne diseases and crop pests. Driving endosymbionts have already been deployed to combat the transmission of dengue and Zika virus in mosquitoes. However, there are a variety of barriers to successfully implementing gene drive techniques in wild populations. There is a risk that targeted organisms will rapidly evolve an ability to suppress the synthetic drive system, rendering it ineffective. There are also potential risks of synthetic gene drivers invading non-target species or populations. This Special Feature covers the current state of affairs regarding both natural and synthetic gene drive systems with the aim to identify knowledge gaps. By understanding how natural drive systems spread through populations, we may be able to better predict the outcomes of synthetic drive release.

Baseline Characterization of Dengue Epidemiology in Yogyakarta City, Indonesia, before a Randomized Controlled Trial of Wolbachia for Arboviral Disease Control

Dengue is endemic in Indonesia. Here, we describe the epidemiology of dengue in the city of Yogyakarta, Central Java, as a prelude to implementation of a cluster-randomized trial of Wolbachia for the biocontrol of arboviral transmission. Surveillance records from 2006 to 2016 demonstrate seasonal oscillations of dengue incidence with varying magnitude. Two lines of evidence demonstrate a high force of infection; the hospitalized case burden of patients diagnosed with dengue hemorrhagic fever or dengue shock syndrome over the last decade consisted predominantly of children/adolescents, and a serosurvey of 314 healthy children aged 1–10 years found 68% possessed dengue virus–neutralizing antibodies. Finally, a mobility survey indicated children aged 1–10 years, and particularly 1–5 year-olds, spent most of their daytime hours at home. These findings inform the design of clinical trials to measure the impact of novel vector control methods such as Wolbachia introgression into Aedes aegypti mosquitoes, by providing baseline data on disease incidence and identifying subpopulations for recruitment into prospective studies of dengue virus infection and disease. The mobility survey findings indicate that in cluster trials of interventions applied at the community level, young children can reasonably be expected to spend most of their exposure time, in epidemiological terms, within the treatment arm to which they were randomized.

Estimating the burden of dengue and the impact of release of wMel Wolbachia-infected mosquitoes in Indonesia: a modelling study

BACKGROUND

Wolbachia-infected mosquitoes reduce dengue virus transmission, and city-wide releases in Yogyakarta city, Indonesia, are showing promising entomological results. Accurate estimates of the burden of dengue, its spatial distribution and the potential impact of Wolbachia are critical in guiding funder and government decisions on its future wider use.

METHODS

Here, we combine multiple modelling methods for burden estimation to predict national case burden disaggregated by severity and map the distribution of burden across the country using three separate data sources. An ensemble of transmission models then predicts the estimated reduction in dengue transmission following a nationwide roll-out of wMel Wolbachia.

RESULTS

We estimate that 7.8 million (95% uncertainty interval [UI] 1.8-17.7 million) symptomatic dengue cases occurred in Indonesia in 2015 and were associated with 332,865 (UI 94,175-754,203) lost disability-adjusted life years (DALYs). The majority of dengue's burden was due to non-severe cases that did not seek treatment or were challenging to diagnose in outpatient settings leading to substantial underreporting. Estimated burden was highly concentrated in a small number of large cities with 90% of dengue cases occurring in 15.3% of land area. Implementing a nationwide Wolbachia population replacement programme was estimated to avert 86.2% (UI 36.2-99.9%) of cases over a long-term average.

CONCLUSIONS

These results suggest interventions targeted to the highest burden cities can have a disproportionate impact on dengue burden. Area-wide interventions, such as Wolbachia, that are deployed based on the area covered could protect people more efficiently than individual-based interventions, such as vaccines, in such dense environments.

The impact of large-scale deployment of Wolbachia mosquitoes on dengue and other Aedes-borne diseases in Rio de Janeiro and Niterói, Brazil: study protocol for a controlled interrupted time series analysis using routine disease surveillance data

Background: Rio de Janeiro and Niterói are neighbouring cities in southeastern Brazil which experience large dengue epidemics every 2 to 5 years, with >100,000 cases notified in epidemic years. Costs of vector control and direct and indirect costs due to the Aedes-borne diseases dengue, chikungunya and Zika were estimated to total $650 million USD in 2016, but traditional vector control strategies have not been effective in preventing mosquito-borne disease outbreaks. The Wolbachia method is a novel and self-sustaining approach for the biological control of Aedes-borne diseases, in which the transmission potential of Aedes aegypti mosquitoes is reduced by stably transfecting them with the Wolbachia bacterium ( wMel strain). This paper describes a study protocol for evaluating the effect of large-scale non-randomised releases of Wolbachia­-infected mosquitoes on the incidence of dengue, Zika and chikungunya in the two cities of Niterói and Rio de Janeiro. This follows a lead-in period since 2014 involving intensive community engagement, regulatory and public approval, entomological surveys, and small-scale pilot releases.

Method: The Wolbachia releases during 2017-2019 covered a combined area of 170 km ² with a resident population of 1.2 million, across Niterói and Rio de Janeiro. Untreated areas with comparable historical dengue profiles and demographic characteristics have been identified a priori as comparative control areas in each city. The proposed pragmatic epidemiological approach combines a controlled interrupted time series analysis of routinely notified suspected and laboratory-confirmed dengue and chikungunya cases, together with monitoring of Aedes-borne disease activity utilising outbreak signals routinely used in public health disease surveillance.

Discussion: If the current project is successful, this model for control of mosquito-borne disease through Wolbachia releases can be expanded nationally and regionally.

The impact of large-scale deployment of Wolbachia mosquitoes on dengue and other Aedes-borne diseases in Rio de Janeiro and Niterói, Brazil: study protocol for a controlled interrupted time series analysis using routine disease surveillance data

Background: Rio de Janeiro and Niterói are neighbouring cities in southeastern Brazil which experience large dengue epidemics every 2 to 5 years, with >100,000 cases notified in epidemic years. Costs of vector control and direct and indirect costs due to the Aedes-borne diseases dengue, chikungunya and Zika were estimated to total $650 million USD in 2016, but traditional vector control strategies have not been effective in preventing mosquito-borne disease outbreaks. The Wolbachia method is a novel and self-sustaining approach for the biological control of Aedes-borne diseases, in which the transmission potential of Aedes aegypti mosquitoes is reduced by stably transfecting them with the Wolbachia bacterium ( wMel strain). This paper describes a study protocol for evaluating the effect of large-scale non-randomised releases of Wolbachia--infected mosquitoes on the incidence of dengue, Zika and chikungunya in the two cities of Niterói and Rio de Janeiro. This follows a lead-in period since 2014 involving intensive community engagement, regulatory and public approval, entomological surveys, and small-scale pilot releases. Method: The Wolbachia releases during 2017-2019 covered a combined area of 170 km ² with a resident population of 1.2 million, across Niterói and Rio de Janeiro. Untreated areas with comparable historical dengue profiles and demographic characteristics have been identified a priori as comparative control areas in each city. The proposed pragmatic epidemiological approach combines a controlled interrupted time series analysis of routinely notified suspected and laboratory-confirmed dengue and chikungunya cases, together with monitoring of Aedes-borne disease activity utilising outbreak signals routinely used in public health disease surveillance. Discussion: If the current project is successful, this model for control of mosquito-borne disease through Wolbachia releases can be expanded nationally and regionally.

Prevalence and Distribution of Dengue Virus in Aedes aegypti in Yogyakarta City before Deployment of Wolbachia Infected Aedes aegypti

Indonesia is one of the countries where dengue infection is prevalent. In this study we measure the prevalence and distribution of dengue virus (DENV) DENV-infected Aedes aegypti in Yogyakarta City, Indonesia, during the wet season when high dengue transmission period occurred, as baseline data before implementation of a Wolbachia-infected Aedes aegypti trial for dengue control. We applied One-Step Multiplex Real Time PCR (RT-PCR) for the type-specific-detection of dengue viruses in field-caught adult Aedes aegypti mosquitoes. In a prospective field study conducted from December 2015 to May 2016, adult female Aedes aegypti were caught from selected areas in Yogyakarta City, and then screened by using RT-PCR. During the survey period, 36 (0.12%) mosquitoes from amongst 29,252 female mosquitoes were positive for a DENV type. In total, 22.20% of dengue-positive mosquitoes were DENV-1, 25% were DENV-2, 17% were DENV-3, but none were positive for DENV-4. This study has provided dengue virus infection prevalence in field-caught Aedes aegypti and its circulating serotype in Yogyakarta City before deployment of Wolbachia-infected Aedes aegypti.