Use of transgenic Aedes aegypti in Brazil: risk perception and assessment

Mosquito and global dengue cases in a warming world

Dengue presents a significant global health challenge, affecting 50-100 symptomatic infections every year and placing immense strain on healthcare systems in tropical and subtropical regions. However, future projections of dengue infections in a warming world remain unclear. We used the support vector machine (SVM) and artificial neural network (ANN) models with Aedes mosquitoes and dengue records from 1960 to 2019 to comprehensively assess the effects of climate change and socioeconomic conditions on the distribution of mosquitoes and the global dengue incidence rate. The SVM and ANN models were applied to project the global future incidence rate and infections during 2021-2040, 2041-2060 and 2061-2080 under various climate change and socioeconomic conditions in a 5 km spatial resolution. We found a geographical distribution expansion of Aedes mosquitoes and dengue in future years, especially in higher latitudes such as North America and Europe. It was estimated that 77 (confidence interval: 40 to 198) million yearly global infections will occur during 2041-2060 under the Shared Socio-economic Pathway SSP2-4.5, a 57% increase of 49 (26-127) million compared with 2000-2019. The rise in annual infections is primarily attributed to the growing incidence rates driven by rising temperatures and the enhanced suitability of Aedes aegypti, and an expanding human population. Our high-resolution projection provides support to local control measures to minimise health impacts from dengue. Specifically, the Aedes mosquito control programmes such as eliminating the Ae. aegypti breeding sites are recommended in Africa and South Asia, where dengue is particularly severe in all climate change and socioeconomic conditions.

Influence of different host blood meal sources on the reproductive outcomes in Anopheles gambiae: Enhancing fecundity in a mass rearing environment

Identification of blood sources for maximum production of Anopheles mosquitoes is an important consideration for colony maintenance which involves mass rearing. High feeding rates, eggs production, hatching rates, larval, pupal, and adult survivorship are essential parameters to consider when selecting a blood host for mass production of An. gambiae. Here, we investigated the feeding success, reproduction performance and survivorship of An. gambiae when fed on blood from five different hosts: cow, goat, sheep, pig, and chicken compared to human blood. There was significant variations in feeding success (F5, 18 =  35.34, p < .001), egg laying (F 5,18 = 12.57, p < .001), number of eggs laid (F5, 18 = 34.23 p < .001), egg hatchability (F 5, 114 =  37.63, p < .001), pupation time (F 5,18 =  5.532763, p = 0.0029) and pupation rates (F 5,18 =  8.26, p < .001). Feeding success was highest in human blood meal (Mean = 125.25 ±  3.86), followed by pig blood meal (Mean = 123 ±  7.93), with no statistically significant difference between the two. The highest proportion of females that laid eggs were those fed on human blood (Mean =  36.50 ±  2.08) followed by those fed on chicken blood meals (Mean =  27.50 ±  5.44) and then pig blood meal (Mean =  26.25 ±  2.87). The mean number of eggs laid per mosquito was highest among those fed on human blood meal (111.65 ±  5.74) followed by those fed on pig blood meal (100.46 ±  6.36). The most favorable outcomes were observed with human blood for hatchability (88.35 ±  5.61%), pig blood for pupation percentage (Mean =  83.50 ±  4.79), and goat blood for pupation time (9.79 ±  0.41 days). Larval survival rates did not significantly differ among blood meal sources (F 5,92 =  0.13, p = 0.985). Nonetheless, the highest survival rate was observed with pig blood meal (Mean =  0.57 ±  0.11). Survival rates of adult F1 varied significantly across blood meals (F 6,346 = 133.19, p < .001), with human blood meal showing the highest survival rate (Mean =  0.73 ±  0.04). However, pig blood meal (56 days) demonstrated the longest survival period, close to human blood meal (57 days). This study revealed pig blood as an excellent alternative to human blood meal for the mass production of An. gambiae.

An Overview of Zika Virus and Zika Virus Induced Neuropathies

Flaviviruses pose a major public health concern across the globe. Among them, Zika virus (ZIKV) is an emerging and reemerging arthropod-borne flavivirus that has become a major international public health problem following multiple large outbreaks over the past two decades. The majority of infections caused by ZIKV exhibit mild symptoms. However, the virus has been found to be associated with a variety of congenital neural abnormalities, including microcephaly in children and Guillain-Barre syndrome in adults. The exact prediction of the potential of ZIKV transmission is still enigmatic and underlines the significance of routine detection of the virus in suspected areas. ZIKV transmission from mother to fetus (including fetal abnormalities), viral presence in immune-privileged areas, and sexual transmission demonstrate the challenges in understanding the factors governing viral persistence and pathogenesis. This review illustrates the transmission patterns, epidemiology, control strategies (through vaccines, antivirals, and vectors), oncolytic aspects, molecular insights into neuro-immunopathogenesis, and other neuropathies caused by ZIKV. Additionally, we summarize in vivo and in vitro models that could provide an important platform to study ZIKV pathogenesis and the underlying governing cellular and molecular mechanisms.

Dengue as a Disease Threatening Global Health: A Narrative Review Focusing on Latin America and Brazil

Arboviruses constitute the largest known group of viruses. These viruses are the etiological agents of pathologies known as arboviruses, with dengue being one of the most prevalent. Dengue has resulted in important socioeconomic burdens placed on different countries around the world, including those in Latin America, especially Brazil. Thus, this work intends to carry out a narrative-based review of the literature, conducted using a study of the secondary data developed through a survey of scientific literature databases, and to present the situation of dengue, particularly its distribution in these localities. Our findings from the literature demonstrate the difficulties that managers face in controlling the spread of and planning a response against dengue, pointing to the high cost of the disease for public coffers, rendering the resources that are already limited even scarcer. This can be associated with the different factors that affect the spread of the disease, including ecological, environmental, and social factors. Thus, in order to combat the disease, it is expected that targeted and properly coordinated public policies need to be adopted not only in specific localities, but also globally.

Modeling impact and cost-effectiveness of driving-Y gene drives for malaria elimination in the Democratic Republic of the Congo

Malaria elimination will be challenging in countries that currently continue to bear high malaria burden. Sex-ratio-distorting gene drives, such as driving-Y, could play a role in an integrated elimination strategy if they can effectively suppress vector populations. Using a spatially explicit, agent-based model of malaria transmission in eight provinces spanning the range of transmission intensities across the Democratic Republic of the Congo, we predict the impact and cost-effectiveness of integrating driving-Y gene drive mosquitoes in malaria elimination strategies that include existing interventions such as insecticide-treated nets and case management of symptomatic malaria. Gene drive mosquitoes could eliminate malaria and were the most cost-effective intervention overall if the drive component was highly effective with at least 95% X-shredder efficiency at relatively low fertility cost, and associated cost of deployment below 7.17 $int per person per year. Suppression gene drive could be a cost-effective supplemental intervention for malaria elimination, but tight constraints on drive effectiveness and cost ceilings may limit its feasibility.

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

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

The Antiviral Small-Interfering RNA Pathway Induces Zika Virus Resistance in Transgenic Aedes aegypti

The resurgence of arbovirus outbreaks across the globe, including the recent Zika virus (ZIKV) epidemic in 2015–2016, emphasizes the need for innovative vector control methods. In this study, we investigated ZIKV susceptibility to transgenic Aedes aegypti engineered to target the virus by means of the antiviral small-interfering RNA (siRNA) pathway. The robustness of antiviral effector expression in transgenic mosquitoes is strongly influenced by the genomic insertion locus and transgene copy number; we therefore used CRISPR/Cas9 to re-target a previously characterized locus (Chr2:321382225) and engineered mosquitoes expressing an inverted repeat (IR) dsRNA against the NS3/4A region of the ZIKV genome. Small RNA analysis revealed that the IR effector triggered the mosquito’s siRNA antiviral pathway in bloodfed females. Nearly complete (90%) inhibition of ZIKV replication was found in vivo in both midguts and carcasses at 7 or 14 days post-infection (dpi). Furthermore, significantly fewer transgenic mosquitoes contained ZIKV in their salivary glands (p = 0.001), which led to a reduction in the number of ZIKV-containing saliva samples as measured by transmission assay. Our work shows that Ae. aegypti innate immunity can be co-opted to engineer mosquitoes resistant to ZIKV.

Antiviral Effectors and Gene Drive Strategies for Mosquito Population Suppression or Replacement to Mitigate Arbovirus Transmission by Aedes aegypti

The mosquito vector Aedes aegypti transmits arthropod-borne viruses (arboviruses) of medical importance, including Zika, dengue, and yellow fever viruses. Controlling mosquito populations remains the method of choice to prevent disease transmission. Novel mosquito control strategies based on genetically manipulating mosquitoes are being developed as additional tools to combat arbovirus transmission. Genetic control of mosquitoes includes two basic strategies: population suppression and population replacement. The former aims to eliminate mosquito populations while the latter aims to replace wild populations with engineered, pathogen-resistant mosquitoes. In this review, we outline suppression strategies being applied in the field, as well as current antiviral effector genes that have been characterized and expressed in transgenic Ae. aegypti for population replacement. We discuss cutting-edge gene drive technologies that can be used to enhance the inheritance of effector genes, while highlighting the challenges and opportunities associated with gene drives. Finally, we present currently available models that can estimate mosquito release numbers and time to transgene fixation for several gene drive systems. Based on the recent advances in genetic engineering, we anticipate that antiviral transgenic Ae. aegypti exhibiting gene drive will soon emerge; however, close monitoring in simulated field conditions will be required to demonstrate the efficacy and utility of such transgenic mosquitoes.

A typology of community and stakeholder engagement based on documented examples in the field of novel vector control

Background

Despite broad consensus on the importance of community and stakeholder engagement (CSE) for guiding the development, regulation, field testing, and deployment of emerging vector control technologies (such as genetically engineered insects), the types of activities pursued have varied widely, as have the outcomes. We looked to previous CSE efforts for clarity about appropriate methods and goals. Our analysis yielded a typology of CSE, and related vocabulary, that describes distinctions that funders, organizers, and scholars should make when proposing or evaluating CSE.

Methods

We compiled available formal documentation of CSE projects, starting with projects mentioned in interviews with 17 key informants. Major features of these examples, including the initiators, target groups, timing, goals, and methods were identified using qualitative coding. Based on these examples, subcategories were developed for a subset of features and applied to the identified cases of CSE in the documents. Co-occurrence of subcategorized features was examined for patterns.

Results

We identified 14 documented examples CSE projects, which were comprised of 28 distinct CSE activities. We found no clear patterns with respect to timing. However, we found that grouping examples according to whether initiators or targets could enact the immediate desired outcome could help to clarify relationships between goals, methods, and targets.

Conclusion

Based on this analysis, we propose a typology that distinguishes three categories of CSE: engagement to inquire –where initiators are empowered to act on information collected through engagement with target groups; engagement to influence –where initiators engage to affect the actions of already-empowered target groups; and engagement to involve –where initiators engage to delegate authority to target groups. The proposed typology can serve as a guide for establishing the goals, identifying appropriate methods, and evaluating and reporting CSE projects by directing attention to important questions to be asked well before determining who to engage and how.

Mosquito borne diseases, such as malaria and dengue, are major causes of illness and death worldwide. Furthermore, it is getting harder to control mosquitoes and other disease-carrying pests because global climate change is facilitating their spread to new areas, and over time, mosquitoes develop resistance to pesticides. Scientists are therefore developing new methods for controlling mosquito vectors using new gene editing tools. However, releasing genetically engineered insects into the environment is controversial. Many experts recommend that communities and stakeholders be consulted about if or how to use these new methods, but there are few guidelines for the best way to do this. We examined published accounts of community and stakeholder engagement pertaining to novel vector control and looked for patterns across these cases. We found that many efforts were not described in published sources, but those that were could be grouped into three categories: engagement to inquire, engagement to influence, and engagement to involve.

Simple framework for real-time forecast in a data-limited situation: the Zika virus (ZIKV) outbreaks in Brazil from 2015 to 2016 as an example

Background

In 2015–2016, Zika virus (ZIKV) caused serious epidemics in Brazil. The key epidemiological parameters and spatial heterogeneity of ZIKV epidemics in different states in Brazil remain unclear. Early prediction of the final epidemic (or outbreak) size for ZIKV outbreaks is crucial for public health decision-making and mitigation planning. We investigated the spatial heterogeneity in the epidemiological features of ZIKV across eight different Brazilian states by using simple non-linear growth models.

Results

We fitted three different models to the weekly reported ZIKV cases in eight different states and obtained an R² larger than 0.995. The estimated average values of basic reproduction numbers from different states varied from 2.07 to 3.41, with a mean of 2.77. The estimated turning points of the epidemics also varied across different states. The estimation of turning points nevertheless is stable and real-time. The forecast of the final epidemic size (attack rate) is reasonably accurate, shortly after the turning point. The knowledge of the epidemic turning point is crucial for accurate real-time projection of the outbreak.

Conclusions

Our simple models fitted the epidemic reasonably well and thus revealed the spatial heterogeneity in the epidemiological features across Brazilian states. The knowledge of the epidemic turning point is crucial for real-time projection of the outbreak size. Our real-time estimation framework is able to yield a reliable prediction of the final epidemic size.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3602-9) contains supplementary material, which is available to authorized users.

Characterization of an iron-inducible Haemaphysalis longicornis tick-derived promoter in an Ixodes scapularis-derived tick cell line (ISE6)

Background

Ticks are important vectors of disease-causing pathogens. With the rise of resistance to chemical acaricides, alternative methods in tick control are warranted. Gene manipulation has been successful in controlling mosquitoes and mosquito-borne diseases and is now looked upon as a candidate method to control ticks and tick-borne pathogens. Our previous study has identified the actin and ferritin promoter regions in the Haemaphysalis longicornis tick.

Results

Here, the ferritin-derived promoter from the H. longicornis tick was characterized in silico, and the core promoter sequences and some of its important components were identified. Several truncations of the promoter region were created and inserted to a reporter plasmid to determine the important components for its activity. The activities of the truncated promoters on the Ixodes scapularis tick cell line (ISE6) were measured via a dual luciferase assay using experimental and control reporter genes. To induce the promoter’s activity, transfected ISE6 cells were exposed to ferrous sulfate. The 639 nucleotides truncated promoter showed the highest activity on ISE6 cells when exposed to 1 mM ferrous sulfate.

Conclusion

In this study, we characterized an iron-inducible tick promoter that could be a valuable tool in the development of a gene-manipulation system to control ticks and tick-borne pathogens.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3574-9) contains supplementary material, which is available to authorized users.

Transcriptional activities of two newly identified Haemaphysalis longicornis tick-derived promoter regions in the Ixodes scapularis tick cell line (ISE6)

Ticks are obligate haematophagous ectoparasites considered to be second to mosquitoes as vectors of human diseases and the most important vector for animals. Despite efforts to control tick infestations, they remain a serious health problem. Gene manipulation has been established in mosquitoes and led to the control of mosquito populations and of mosquito-borne pathogens. Therefore, gene manipulation could be useful for controlling ticks and tick-borne pathogens. To investigate effective gene expression vectors for ticks, the promoter activities of commercial plasmids were evaluated in a tick cell line (ISE6). Dual luciferase assays revealed that pmirGLO, the human phosphoglycerate kinase promoter contained plasmid vector, showed the highest activity in ISE6 cells amongst the tested plasmids. Moreover, we identified the promoter regions of the Haemaphysalis longicornis actin (HlAct) and the intracellular ferritin (HlFer1) genes. To construct a more effective expression vector for ticks, these promoter regions were inserted into pmirGLO (pmirGLO-HlAct pro and pmirGLO-HlFer1 pro). The pmirGLO-HlAct pro vector showed significantly higher promoter activity than pmirGLO, whereas the pmirGLO-HlFer1 pro vector demonstrated significantly lower promoter activity than pmirGLO in ISE6 cells. The HlAct promoter region may have high promoter activity in ISE6 cells. The results of the present study provide useful information for the development of a genetic modification system in ticks.

GM insect pests under the Brazilian regulatory framework: development and perspectives

The emergence of new technologies for genetic modification has broadened the range of possible new products. The regulations of many countries that could benefit from these new products may not be prepared to assess risks and enable science-based decision-making. This is especially acute in the case of genetically modified insects with potential use in public health and agriculture. Modifications of the regulatory framework, sometimes necessary to allow a proper risk assessment of products from new technologies, are strongly influenced by political decisions derived from the balance of power and interest among stakeholders. This article discusses the genesis of the Brazilian regulatory framework, its applicability for the risk assessment of genetically modified insects and the scenarios that have shaped the two biosafety laws that established the basis for the use of modern biotechnology in the country. It is concluded that, for the adoption of the new technologies, it is important to carefully navigate the political tensions by seeking the engagement and empowerment of stakeholders supporting science-based decision-making in order to gather the necessary support for adoption of risk assessment as the basis for final decisions, allowing the use of new technologies.

Mosquitoes and the Lymphatic Filarial Parasites: Research Trends and Budding Roadmaps to Future Disease Eradication

The mosquito-borne lymphatic filariasis (LF) is a parasitic, neglected tropical disease that imposes an unbearable human scourge. Despite the unprecedented efforts in mass drug administration (MDA) and morbidity management, achieving the global LF elimination slated for the year 2020 has been thwarted by limited MDA coverage and ineffectiveness in the chemotherapeutic intervention. Moreover, successful and sustainable elimination of mosquito-vectored diseases is often encumbered by reintroduction and resurgence emanating from human residual or new infections being widely disseminated by the vectors even when chemotherapy proves effective, but especially in the absence of effective vaccines. This created impetus for strengthening the current defective mosquito control approach, and profound research in vector⁻pathogen systems and vector biology has been pushing the boundaries of ideas towards developing refined vector-harnessed control strategies. Eventual implementation of these emerging concepts will offer a synergistic approach that will not only accelerate LF elimination, but also augurs well for its future eradication. This brief review focuses on advances in mosquito⁻filaria research and considers the emerging prospects for future eradication of LF.

Zika virus: An updated review of competent or naturally infected mosquitoes

Zika virus (ZIKV) is an arthropod-borne virus (arbovirus) that recently caused outbreaks in the Americas. Over the past 60 years, this virus has been observed circulating among African, Asian, and Pacific Island populations, but little attention has been paid by the scientific community until the discovery that large-scale urban ZIKV outbreaks were associated with neurological complications such as microcephaly and several other neurological malformations in fetuses and newborns. This paper is a systematic review intended to list all mosquito species studied for ZIKV infection or for their vector competence. We discuss whether studies on ZIKV vectors have brought enough evidence to formally exclude other mosquitoes than Aedes species (and particularly Aedes aegypti) to be ZIKV vectors. From 1952 to August 15, 2017, ZIKV has been studied in 53 mosquito species, including 6 Anopheles, 26 Aedes, 11 Culex, 2 Lutzia, 3 Coquillettidia, 2 Mansonia, 2 Eretmapodites, and 1 Uranotaenia. Among those, ZIKV was isolated from 16 different Aedes species. The only species other than Aedes genus for which ZIKV was isolated were Anopheles coustani, Anopheles gambiae, Culex perfuscus, and Mansonia uniformis. Vector competence assays were performed on 22 different mosquito species, including 13 Aedes, 7 Culex, and 2 Anopheles species with, as a result, the discovery that A. aegypti and Aedes albopictus were competent for ZIKV, as well as some other Aedes species, and that there was a controversy surrounding Culex quinquefasciatus competence. Although Culex, Anopheles, and most of Aedes species were generally observed to be refractory to ZIKV infection, other potential vectors transmitting ZIKV should be explored.

Household Dengue Prevention Interventions, Expenditures, and Barriers to Aedes aegypti Control in Machala, Ecuador

The Aedes aegypti mosquito is an efficient vector for the transmission of Zika, chikungunya, and dengue viruses, causing major epidemics and a significant social and economic burden throughout the tropics and subtropics. The primary means of preventing these diseases is household-level mosquito control. However, relatively little is known about the economic burden of Ae. aegypti control in resource-limited communities. We surveyed residents from 40 households in a high-risk community at the urban periphery in the city of Machala, Ecuador, on dengue perceptions, vector control interventions, household expenditures, and factors influencing purchasing decisions. The results of this study show that households spend a monthly median of US$2.00, or 1.90% (range: 0.00%, 9.21%) of their family income on Ae. aegypti control interventions. Households reported employing, on average, five different mosquito control and dengue prevention interventions, including aerosols, liquid sprays, repellents, mosquito coils, and unimpregnated bed nets. We found that effectiveness and cost were the most important factors that influence people's decisions to purchase a mosquito control product. Our findings will inform the development and deployment of new Ae. aegypti control interventions by the public health and private sectors, and add to prior studies that have focused on the economic burden of dengue-like illness.

Novel Vector Control Approaches: The Future for Prevention of Zika Virus Transmission?

In a Perspective accompanying Abad-Franch and colleagues, Lorenz von Seidlein, Alexander Kekulé, and Daniel Strickman discuss the importance of developing effective strategies to minimize mosquito-borne transmission of human diseases.