New self-sexing Aedes aegypti strain eliminates barriers to scalable and sustainable vector control for governments and communities in dengue-prone environments

Understanding the genetics of sex determination in insects and its relevance to genetic pest management

Sex determination pathways regulate male and female-specific development and differentiation and offer potential targets for genetic pest management methods. Insect sex determination pathways are comprised of primary signals, relay genes and terminal genes. Primary signals of coleopteran, dipteran, hymenopteran and lepidopteran species are highly diverse and regulate the sex-specific splicing of relay genes based on the primary signal dosage, amino acid composition or the interaction with paternally inherited genes. In coleopterans, hymenopterans and some dipterans, relay genes are Transformer orthologs from the serine-arginine protein family that regulate sex-specific splicing of the terminal genes. Alternative genes regulate the splicing of the terminal genes in dipterans that lack Transformer orthologs and lepidopterans. Doublesex and Fruitless orthologs are the terminal genes. Doublesex and Fruitless orthologs are highly conserved zinc-finger proteins that regulate the expression of downstream proteins influencing physical traits and courtship behaviours in a sex-specific manner. Genetic pest management methods can use different mechanisms to exploit or disrupt female-specific regions of different sex determination genes. Female-specific regions of sex determination genes can be exploited to produce a lethal gene only in females or disrupted to impede female development or fertility. Reducing the number of fertile females in pest populations creates a male-biased sex ratio and eventually leads to the local elimination of the pest population. Knowledge on the genetic basis of sex determination is important to enable these sex determination pathways to be exploited for genetic pest management.

Differential elimination of marked sex chromosomes enables production of nontransgenic male mosquitoes in a single strain

Diverse genetic strategies are being pursued to control mosquito-borne infectious diseases. These strategies often rely on the release of nonbiting males to either reduce the target mosquito population or render them resistant to pathogens. Male-only releases are important as any contaminating females can bite and potentially transmit pathogens. Despite significant efforts, it remains a major bottleneck to reliably and efficiently separate males from females, especially when nontransgenic males are preferred. In the yellow fever mosquito Aedes aegypti, sex is determined by a pair of homomorphic sex chromosomes, with the dominant male-determining locus (the M locus) and its counterpart (the m locus) embedded in an M-bearing and an m-bearing chromosome 1, respectively. We utilized both naturally occurring and engineered sex-linked recessive lethal alleles (RLAs) to create sex separation strains for Ae. aegypti on the basis of differential elimination of marked sex chromosomes (DeMark). DeMark strains are self-sustaining and produce nontransgenic males that are readily separated from individuals carrying RLA- and transgene-marked m chromosomes. For example, the marked m chromosome in the heterozygous mother in some strains was only inherited by her female progeny due to RLA-mediated incompatibility with the M-bearing chromosome in the father, producing nontransgenic males and transgenic females, generation after generation. We further explore strategies to conditionally eliminate females that contain marked sex chromosomes. We also discuss DeMark designs that are applicable for efficient sex separation in organisms with well-differentiated X and Y chromosomes, such as the Anopheles mosquitoes.

Successful insertion and expression of a tetracycline transactivator in Anopheles stephensi associated with increased egg production and decreased hatching rate

Sanaria® has pioneered production of aseptic, purified, vialed cryopreserved Plasmodium falciparum (Pf) sporozoites (SPZ) as vaccines and for controlled human malaria infections. More than 3,500 individuals have received more than 9,700 injections of PfSPZ, worldwide. The PfSPZ are manufactured in aseptically reared female Anopheles stephensi mosquitoes. Since PfSPZ vaccines are intended primarily for some of the most disadvantaged people in the world, keeping costs low is imperative. One approach to reducing cost of goods is to eliminate male mosquitoes from the production process, thereby doubling the numbers of PfSPZ-producing mosquitoes per unit space. We intend to do this by creating A. stephensi with a male-lethal allele controlled by the tetracycline conditional gene expression system. Herein, we report the first step in this process, the creation of a driver line that expresses the reverse tetracycline transactivator (rtTA). After sub-optimal results using the bZip early embryonic promoter, we produced 3 mosquito driver lines that expressed rtTA from 3 different genomic loci under the early embryonic vasa promoter. Expressing the rtTA under the vasa promoter significantly increased rtTA mRNA levels compared to its level under bZip. We were unable to achieve homozygosity in two of these lines even after 26 generations. In the third line, the insertion was in an intron of a putative juvenile hormone diol kinase gene. Homozygosity was reached in this line after passage through 7 generations, indicating that the inserted vasa-rtTA nucleotides did not interfere with the function of an essential genomic locus. rtTA mRNA expression levels were higher than in the other two lines, supporting the hypothesis that failure to achieve homozygosity was not due to rtTA expression but to insertion position. The homozygous line produced ~ 18% more eggs per female and a hatching rate of larvae from eggs was 39% lower than of wild-type A. stephensi. The next step will be to cross the driver line with an effector line containing a male-linked lethal gene regulated by the tetracycline responsive element (TRE).

Synthetic homing endonuclease gene drives to revolutionise Aedes aegypti biocontrol - game changer or pipe dream?

The increasing burden of Aedes aegypti-borne diseases, particularly dengue, is a growing global concern, further exacerbated by climate change. Current control strategies have proven insufficient, necessitating novel approaches. Synthetic homing endonuclease gene (sHEG) drives represent one of the few emerging technologies with the potential to offer a cost-effective and equitable solution to this escalating public health challenge. However, despite multiple attempts, the homing efficiencies of Ae. aegypti sHEG systems lag behind those achieved in Anopheles mosquitoes. We discuss key insights from efforts to develop sHEGs in Ae. aegypti and highlight critical factors that may unlock further advances in this species.

Exploiting Wolbachia as a Tool for Mosquito-Borne Disease Control: Pursuing Efficacy, Safety, and Sustainability

Despite the application of control measures, mosquito-borne diseases continue to pose a serious threat to human health. In this context, exploiting Wolbachia, a common symbiotic bacterium in insects, may offer effective solutions to suppress vectors or reduce their competence in transmitting several arboviruses. Many Wolbachia strains can induce conditional egg sterility, known as cytoplasmic incompatibility (CI), when infected males mate with females that do not harbor the same Wolbachia infection. Infected males can be mass-reared and then released to compete with wild males, reducing the likelihood of wild females encountering a fertile mate. Furthermore, certain Wolbachia strains can reduce the competence of mosquitoes to transmit several RNA viruses. Through CI, Wolbachia-infected individuals can spread within the population, leading to an increased frequency of mosquitoes with a reduced ability to transmit pathogens. Using artificial methods, Wolbachia can be horizontally transferred between species, allowing the establishment of various laboratory lines of mosquito vector species that, without any additional treatment, can produce sterilizing males or females with reduced vector competence, which can be used subsequently to replace wild populations. This manuscript reviews the current knowledge in this field, describing the different approaches and evaluating their efficacy, safety, and sustainability. Successes, challenges, and future perspectives are discussed in the context of the current spread of several arboviral diseases, the rise of insecticide resistance in mosquito populations, and the impact of climate change. In this context, we explore the necessity of coordinating efforts among all stakeholders to maximize disease control. We discuss how the involvement of diverse expertise-ranging from new biotechnologies to mechanistic modeling of eco-epidemiological interactions between hosts, vectors, Wolbachia, and pathogens-becomes increasingly crucial. This coordination is especially important in light of the added complexity introduced by Wolbachia and the ongoing challenges posed by global change.

A Comparative Assessment of Self-limiting Genetic Control Strategies for Population Suppression

Genetic control strategies are promising solutions for control of pest populations and invasive species. Methods utilizing repeated releases of males such as sterile insect technique (SIT), release of insects carrying a dominant lethal (RIDL), self-limiting gene drives, and gene disruptors are highly controllable methods, ensuring biosafety. Although models of these strategies have been built, detailed comparisons are lacking, particularly for some of the newer strategies. Here, we conducted a thorough comparative assessment of self-limiting genetic control strategies by individual-based simulation models. Specifically, we find that repeated releases greatly enhance suppression power of weak and self-limiting gene drives, enabling population elimination with even low efficiency and high fitness costs. Moreover, dominant female sterility further strengthens self-limiting systems that can either use gene drive or disruptors that target genes without a mechanism to bias their own inheritance. Some of these strategies are highly persistent, resulting in relatively low release ratios even when released males suffer high fitness costs. To quantitatively evaluate different strategies independent from ecological impact, we proposed constant-population genetic load, which achieves over 95% accuracy in predicting simulation outcomes for most strategies, though it is not as precise in a few frequency-dependent systems. Our results suggest that many new self-limiting strategies are safe, flexible, and more cost-effective than traditional SIT and RIDL, and thus have great potential for population suppression of insects and other pests.

Evaluation of ebony as a potential selectable marker for genetic sexing in Aedes aegypti

BACKGROUND

Aedes aegypti is expected to invade previously unoccupied areas, mainly due to the climate change, the increase in travel and trade activities and the continuous transformation of the rural environment into urban areas. The sterile insect technique (SIT), which relies on the mass production and release of sterile males, is an environmentally friendly approach that can be applied for population control of Ae. aegypti. SIT programs can be greatly benefited by a genetic sexing strain (GSS) and a reliable sex sorting system to minimize any accidental female release. Visually detectable or conditionally lethal selectable markers can be used for the development of new GSSs. In this study, we evaluated the suitability and competence of a mutant Ae. aegypti ebony strain for the development of a new GSS. The ebony gene is known to be involved in the pigmentation pathway of several dipteran insects, including Ae. aegypti.

METHODS

An ebony gene knockout was developed though CRISPR/Cas9 mutagenesis. G0 individuals with the desired phenotype were crossed, and progeny were screened in every generation. PCR and sequencing were performed using gDNA from a pulled leg to determine the mutant genotype. Quality control tests, including pupae and adult recovery rates, male sex ratio and fecundity, were applied to the ebony mutant line to determine whether the mutation confers any fitness cost.

RESULTS

An Ae. aegypti ebony knockout mutant carrying a 5-bp deletion was obtained, which presented darker head and siphon phenotypes at the larval stage. However, genetic analysis revealed that this ebony mutation results in incomplete penetrance and variable expressivity. The establishment of a pure ebony mutant line was not possible because of the fitness costs conferred by the mutation.

CONCLUSIONS

In this study, the adequacy and suitability of the ebony gene as a selectable marker for the development of a GSS in Ae. aegypti were assessed. Despite its clear phenotype early in larval development, the homozygous mutant line presented phenotypic inconsistency and loss of fertility. These drawbacks clearly indicate that this particular mutation is not suitable for the development of a new GSS. Nonetheless, it cannot be excluded that a different mutation will lead to a different expression and penetrance profile and a viable homozygous mutant line.

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.

Post-release monitoring pathway for the deployment of gene drive-modified mosquitoes for malaria control in Africa

BACKGROUND

Gene drive-modified mosquitoes (GDMMs) have been promoted as one of the innovative technologies that may control and eliminate malaria and other mosquito-borne diseases. Several products are in early stages of development, targeting either population suppression or population modification of the mosquito vector. However, there is no direct experience of conducting risk assessment for environmental releases and subsequent policies regarding conditions for post-release. This study was carried out to gain additional insights on the possible post-release concerns that may arise, as they may inform future risk assessment and planning for deployment.

METHODS

This study involved desktop reviews on post release monitoring experiences with previously released biological control products. Stakeholder consultations involving online surveys, and face to face workshop with experts from selected African countries from Eastern, Western, and Southern African regions was then carried out to establish post-release monitoring concerns for GDMMs.

RESULTS

Review of genetic biocontrol technologies showed only limited lessons from post-release monitoring regimes with a focus largely limited to efficacy. For genetically modified organisms general surveillance and case-specific monitoring is expected in some of the regions. A number of post-release monitoring concerns in relation to the protection goals of human and animal health, biodiversity, and water quality were identified.

CONCLUSION

Based on established- protection goals, several post-release monitoring concerns have been identified. Subject to a rigorous risk assessment process for future GDMMs products, the concerns may then be prioritized for post-release monitoring.

Improving the suppressive power of homing gene drive by co-targeting a distant-site female fertility gene

Gene drive technology has the potential to address major biological challenges. Well-studied homing suppression drives have been shown to be highly efficient in Anopheles mosquitoes, but for other organisms, lower rates of drive conversion prevent elimination of the target population. To tackle this issue, we propose a gene drive design that has two targets: a drive homing site where drive conversion takes place, and a distant site where cleavage induces population suppression. We model this design and find that the two-target system allows suppression to occur over a much wider range of drive conversion efficiency. Specifically, the cutting efficiency now determines the suppressive power of the drive, rather than the conversion efficiency as in standard suppression drives. We construct a two-target drive in Drosophila melanogaster and show that both components of the gene drive function successfully. However, cleavage in the embryo from maternal deposition as well as fitness costs in female drive heterozygotes both remain significant challenges for both two-target and standard suppression drives. Overall, our improved gene drive design has the potential to ease problems associated with homing suppression gene drives for many species where drive conversion is less efficient.

Population suppression with dominant female-lethal alleles is boosted by homing gene drive

BACKGROUND

Methods to suppress pest insect populations using genetic constructs and repeated releases of male homozygotes have recently been shown to be an attractive alternative to older sterile insect techniques based on radiation. Female-specific lethal alleles have substantially increased power, but still require large, sustained transgenic insect releases. Gene drive alleles bias their own inheritance to spread throughout populations, potentially allowing population suppression with a single, small-size release. However, suppression drives often suffer from efficiency issues, and the most well-studied type, homing drives, tend to spread without limit.

RESULTS

In this study, we show that coupling female-specific lethal alleles with homing gene drive allowed substantial improvement in efficiency while still retaining the self-limiting nature (and thus confinement) of a lethal allele strategy. Using a mosquito model, we show the required release sizes for population elimination in a variety of scenarios, including different density growth curves, with comparisons to other systems. Resistance alleles reduced the power of this method, but these could be overcome by targeting an essential gene with the drive while also providing rescue. A proof-of-principle demonstration of this system in Drosophila melanogaster was effective in both biasing its inheritance and achieving high lethality among females that inherit the construct in the absence of antibiotic.

CONCLUSIONS

Overall, our study shows that substantial improvements can be achieved in female-specific lethal systems for population suppression by combining them with various types of gene drive.

Generating prophylactic immunity against arboviruses in vertebrates and invertebrates

The World Health Organization recently declared a global initiative to control arboviral diseases. These are mainly caused by pathogenic flaviviruses (such as dengue, yellow fever and Zika viruses) and alphaviruses (such as chikungunya and Venezuelan equine encephalitis viruses). Vaccines represent key interventions for these viruses, with licensed human and/or veterinary vaccines being available for several members of both genera. However, a hurdle for the licensing of new vaccines is the epidemic nature of many arboviruses, which presents logistical challenges for phase III efficacy trials. Furthermore, our ability to predict or measure the post-vaccination immune responses that are sufficient for subclinical outcomes post-infection is limited. Given that arboviruses are also subject to control by the immune system of their insect vectors, several approaches are now emerging that aim to augment antiviral immunity in mosquitoes, including Wolbachia infection, transgenic mosquitoes, insect-specific viruses and paratransgenesis. In this Review, we discuss recent advances, current challenges and future prospects in exploiting both vertebrate and invertebrate immune systems for the control of flaviviral and alphaviral diseases.

Altering traits and fates of wild populations with Mendelian DNA sequence modifying Allele Sails

Population-scale genome modification can alter the composition or fate of wild populations. Synthetic gene drives provide one set of tools, but their use is complicated by scientific, regulatory, and social issues associated with transgene persistence and flow. Here we propose an alternative approach. An Allele Sail consists of a genome editor (the Wind) that introduces DNA sequence edits, and is inherited in a Mendelian fashion. Meanwhile, the edits (the Sail) experience an arithmetic, Super-Mendelian increase in frequency. We model this system and identify contexts in which a single, low frequency release of an editor brings edits to a very high frequency. We also identify conditions in which manipulation of sex determination can bring about population suppression. In regulatory frameworks that distinguish between transgenics (GMO) and their edited non-transgenic progeny (non-GMO) Allele Sails may prove useful since the spread and persistence of the GM component can be limited.

Heritable CRISPR Mutagenesis of Essential Maternal Effect Genes as a Simple Tool for Sustained Population Suppression of Invasive Species in a Zebrafish Model

Invasive species control is important for ecological and agricultural management. Genetic methods can provide species specificity for population control. We developed heritable maternal effect embryo lethality (HMEL), a novel strategy allowing negative population pressure from HMEL individuals to be transmitted within a population across generations. We demonstrate the HMEL technique in zebrafish through genome-integrated CRISPR/Cas targeted mutagenic disruption of nucleoplasmin 2b (npm2b), a female-specific essential maternal effect gene, causing heritable sex-limited disruption of reproduction. HMEL-induced high-efficiency mutation of npm2b in females suppresses population, while males transmit the HMEL allele across generations. HMEL could be easily modified to target other genes causing sex-specific sterility, or generalized to control invasive fish or other vertebrate species for environmental conservation or agricultural protection.

Aedes aegypti Controls AE. Aegypti: SIT and IIT-An Overview

The sterile insect technique (SIT) and the incompatible insect technique (IIT) are emerging and potentially revolutionary tools for controlling Aedes aegypti (L.), a prominent worldwide mosquito vector threat to humans that is notoriously difficult to reduce or eliminate in intervention areas using traditional integrated vector management (IVM) approaches. Here we provide an overview of the discovery, development, and application of SIT and IIT to Ae. aegypti control, and innovations and advances in technology, including transgenics, that could elevate these techniques to a worldwide sustainable solution to Ae. aegypti when combined with other IVM practices.

Targeting sex determination to suppress mosquito populations

Each year, hundreds of millions of people are infected with arboviruses such as dengue, yellow fever, chikungunya, and Zika, which are all primarily spread by the notorious mosquito Aedes aegypti. Traditional control measures have proven insufficient, necessitating innovations. In response, here we generate a next-generation CRISPR-based precision-guided sterile insect technique (pgSIT) for Ae. aegypti that disrupts genes essential for sex determination and fertility, producing predominantly sterile males that can be deployed at any life stage. Using mathematical models and empirical testing, we demonstrate that released pgSIT males can effectively compete with, suppress, and eliminate caged mosquito populations. This versatile species-specific platform has the potential for field deployment to effectively control wild populations of disease vectors.

Manipulating the Destiny of Wild Populations Using CRISPR

Genetic biocontrol aims to suppress or modify populations of species to protect public health, agriculture, and biodiversity. Advancements in genome engineering technologies have fueled a surge in research in this field, with one gene editing technology, CRISPR, leading the charge. This review focuses on the current state of CRISPR technologies for genetic biocontrol of pests and highlights the progress and ongoing challenges of using these approaches.

HM, Zhan Y, DeBeaubien NA, Loh YM, Su MP, Montell C, Marshall JM, Akbari OS. Targeting Sex Determination to Suppress Mosquito Populations

Each year, hundreds of millions of people are infected with arboviruses such as dengue, yellow fever, chikungunya, and Zika, which are all primarily spread by the notorious mosquito Aedes aegypti. Traditional control measures have proven insufficient, necessitating innovations. In response, here we generate a next generation CRISPR-based precision-guided sterile insect technique (pgSIT) for Aedes aegypti that disrupts genes essential for sex determination and fertility, producing predominantly sterile males that can be deployed at any life stage. Using mathematical models and empirical testing, we demonstrate that released pgSIT males can effectively compete with, suppress, and eliminate caged mosquito populations. This versatile species-specific platform has the potential for field deployment to effectively control wild populations of disease vectors.

Zoonotic mosquito-borne arboviruses: Spillover, spillback, and realistic mitigation strategies

Emerging zoonotic mosquito-borne viruses pose increasing health threats because of growing mosquito population, geographic expansions, and control challenges. We emphasize the need for global preparedness to effectively mitigate the health, societal, and economic impacts of spillover by these viruses through proactive measures of prediction, surveillance, prevention, and treatment.

Efficient Sex Separation by Exploiting Differential Alternative Splicing of a Dominant Marker in Aedes aegypti

Only female mosquitoes consume blood and transmit deadly human pathogens. Therefore, it is critical to remove females before conducting releases for genetic biocontrol interventions. Here we describe a robust sex-sorting approach termed SEPARATOR (Sexing Element Produced by Alternative RNA-splicing of A Transgenic Observable Reporter) that exploits sex-specific alternative splicing of an innocuous reporter to ensure exclusive dominant male-specific expression. Using SEPARATOR, we demonstrate reliable sex selection from larval and pupal stages in Aedes aegypti, and use a Complex Object Parametric Analyzer and Sorter (COPAS®) to demonstrate scalable high-throughput sex-selection of first instar larvae. Additionally, we use this approach to sequence the transcriptomes of early larval males and females and find several genes that are sex-specifically expressed in males. SEPARATOR can simplify mass production of males for release programs and is designed to be cross-species portable and should be instrumental for genetic biocontrol interventions.

Requirements for market entry of gene drive-modified mosquitoes for control of vector-borne diseases: analogies to other biologic and biotechnology products

Gene drive-modified mosquitoes (GDMMs) are proposed as new tools for control and elimination of malaria and other mosquito-borne diseases, and promising results have been observed from testing conducted in containment. Although still at an early stage of development, it is important to begin now to consider approval procedures and market entry strategies for the eventual implementation of GDMMs in the context of disease control programs, as these could impact future research plans. It is expected that, as for other types of new products, those seeking to bring GDMMs to market will be required to provide sufficient information to allow the regulator(s) to determine whether the product is safe and effective for its proposed use. There already has been much emphasis on developing requirements for the biosafety components of the "safe and effective" benchmark, largely concerned with their regulation as genetically modified organisms. Other potential approval requirements have received little attention, however. Although GDMMs are expected to be implemented primarily in the context of public health programs, any regulatory analogies to other public health products, such as pharmaceuticals, vaccines, or chemical pesticides, must take into account the characteristics of live mosquito products. Typical manufacturing standards related to product identity, potency or quality will need to be adapted to GDMMs. Valuable lessons can be drawn from the regulatory approval processes for other whole organism and genetically modified (GM) organism products. Supply chain requirements, such as scale of production, location and design of production facilities, and methods of distribution and delivery, will be dependent upon the characteristics of the particular GDMM product, the conditions of use, and the region to be served. Plans for fulfilling supply chain needs can build upon experience in the development of other live insect products for use in public health and agriculture. Implementation of GDMMs would benefit from additional research on enabling technologies for long-term storage of mosquito life stages, efficient mass production, and area-wide delivery of GDMMs. Early consideration of these practical requirements for market entry will help to mitigate downstream delays in the development of these promising new technologies.

Targeting Sex Determination to Suppress Mosquito Populations

Each year, hundreds of millions of people are infected with arboviruses such as dengue, yellow fever, chikungunya, and Zika, which are all primarily spread by the notorious mosquito Aedes aegypti. Traditional control measures have proven insuficient, necessitating innovations. In response, here we generate a next generation CRISPR-based precision-guided sterile insect technique (pgSIT) for Aedes aegypti that disrupts genes essential for sex determination and fertility, producing predominantly sterile males that can be deployed at any life stage. Using mathematical models and empirical testing, we demonstrate that released pgSIT males can effectively compete with, suppress, and eliminate caged mosquito populations. This versatile species-specific platform has the potential for field deployment to control wild populations, safely curtailing disease transmission.

The Promise and Challenge of Genetic Biocontrol Approaches for Malaria Elimination

Malaria remains an ongoing public health challenge, with over 600,000 deaths in 2021, of which approximately 96% occurred in Africa. Despite concerted efforts, the goal of global malaria elimination has stalled in recent years. This has resulted in widespread calls for new control methods. Genetic biocontrol approaches, including those focused on gene-drive-modified mosquitoes (GDMMs), aim to prevent malaria transmission by either reducing the population size of malaria-transmitting mosquitoes or making the mosquitoes less competent to transmit the malaria parasite. The development of both strategies has advanced considerably in recent years, with successful field trials of several biocontrol methods employing live mosquito products and demonstration of the efficacy of GDMMs in insectary-based studies. Live mosquito biocontrol products aim to achieve area-wide control with characteristics that differ substantially from current insecticide-based vector control methods, resulting in some different considerations for approval and implementation. The successful field application of current biocontrol technologies against other pests provides evidence for the promise of these approaches and insights into the development pathway for new malaria control agents. The status of technical development as well as current thinking on the implementation requirements for genetic biocontrol approaches are reviewed, and remaining challenges for public health application in malaria prevention are discussed.

Regulatory and policy considerations for the implementation of gene drive-modified mosquitoes to prevent malaria transmission

Gene drive-modified mosquitoes (GDMMs) are being developed as possible new tools to prevent transmission of malaria and other mosquito-borne diseases. To date no GDMMs have yet undergone field testing. This early stage is an opportune time for developers, supporters, and possible users to begin to consider the potential regulatory requirements for eventual implementation of these technologies in national or regional public health programs, especially as some of the practical implications of these requirements may take considerable planning, time and coordination to address. Several currently unresolved regulatory questions pertinent to the implementation of GDMMs are examined, including: how the product will be defined; what the registration/approval process will be for placing new GDMM products on the market; how the potential for transboundary movement of GDMMs can be addressed; and what role might be played by existing multinational bodies and agreements in authorization decisions. Regulation and policies applied for registration of other genetically modified organisms or other living mosquito products are assessed for relevance to the use case of GDMMs to prevent malaria in Africa. Multiple national authorities are likely to be involved in decision-making, according to existing laws in place within each country for certain product classes. Requirements under the Cartagena Protocol on Biodiversity will be considered relevant in most countries, as may existing regulatory frameworks for conventional pesticide, medical, and biocontrol products. Experience suggests that standard regulatory processes, evidence requirements, and liability laws differ from country to country. Regional mechanisms will be useful to address some of the important challenges.