CRISPR/Cas9 Mutagenesis in Phlebotomus papatasi: the Immune Deficiency Pathway Impacts Vector Competence for Leishmania major

Leishmania-sand fly interactions: exploring the role of the immune response and potential strategies for Leishmaniasis control

Leishmaniasis is a neglected tropical disease caused by protozoan parasites of the genus Leishmania, affecting millions of people worldwide. The disease is transmitted by the bite of infected female sand flies, which act as vectors and hosts for the parasites. The interaction between Leishmania parasites and sand flies is complex and dynamic, involving various factors that influence parasite development, survival and transmission. This review examines how the immune response of sand flies affects vector competence and transmission of Leishmania parasites, and what the potential strategies are to prevent or reduce infection. The review also summarizes the main findings and conclusions of the existing literature and discusses implications and recommendations for future research and practice. The study reveals that the immune response of sand flies is a key determinant of vector competence and transmission of Leishmania parasites, and that several molecular and cellular mechanisms are involved in the interaction between parasite and vector. The study also suggests that there are potential strategies for controlling leishmaniasis, such as interfering with parasite development, modulating the vector's immune response or reducing the vector population. However, the study also identifies several gaps and limitations in current knowledge and calls for more comprehensive and systematic studies on vector-parasite interaction and its impact on leishmaniasis transmission and control.

Recent development in CRISPR-Cas systems for human protozoan diseases

Protozoan parasitic diseases pose a substantial global health burden. Understanding the pathogenesis of these diseases is crucial for developing intervention strategies in the form of vaccine and drugs. Manipulating the parasite's genome is essential for gaining insights into its fundamental biology. Traditional genomic manipulation methods rely on stochastic homologous recombination events, which necessitates months of maintaining the cultured parasites under drug pressure to generate desired transgenics. The introduction of mega-nucleases (MNs), zinc-finger nucleases (ZFNs), and transcription activator-like effector nucleases (TALENs) greatly reduced the time required for obtaining a desired modification. However, there is a complexity associated with the design of these nucleases. CRISPR (Clustered regularly interspaced short palindromic repeats)/Cas (CRISPR associated proteins) is the latest gene editing tool that provides an efficient and convenient method for precise genomic manipulations in protozoan parasites. In this chapter, we have elaborated various strategies that have been adopted for the use of CRISPR-Cas9 system in Plasmodium, Leishmania and Trypanosoma. We have also discussed various applications of CRISPR-Cas9 pertaining to understanding of the parasite biology, development of drug resistance mechanism, gene drive and diagnosis of the infection.

Mosquito Embryo Microinjection

Genetically modified (GM) mosquitoes are an important tool in the fight against mosquito-borne disease, both indirectly through their use in research investigating host-pathogen interaction, mosquito olfaction, and anthropomorphic behavior and in future direct uses for suppression and possibly eradication through sterile insect technique (SIT) and/or gene-drive programs. Successful creation of GM mosquitoes depends on microinjection procedures that precisely deliver injection materials while causing as little damage to mosquito embryos as possible. Genetic modification reagents, such as transposon system components (vector plasmids, helper plasmids, and helper mRNA), and CRISPR-Cas9 components (guide RNAs, Cas9 protein, plasmids expressing Cas9 and/or guide RNAs, and donor plasmids used in homology-directed repair [HDR]), must be delivered into the preblastoderm embryo at the posterior end where the pole cells will form before cellularization occurs. Sharp needles that pierce the embryo easily are important tools in this procedure and work best when the embryos are not desiccated. The two main procedures for mosquito embryo microinjection involve injecting embryos under halocarbon oil or under aqueous solution.

Arthropod promoters for genetic control of disease vectors

Vector-borne diseases (VBDs) impose devastating effects on human health and a heavy financial burden. Malaria, Lyme disease, and dengue fever are just a few examples of VBDs that cause severe illnesses. The current strategies to control VBDs consist mainly of environmental modification and chemical use, and to a small extent, genetic approaches. The genetic approaches, including transgenesis/genome modification and gene-drive technologies, provide the basis for developing new tools for VBD prevention by suppressing vector populations or reducing their capacity to transmit pathogens. The regulatory elements such as promoters are required for a robust sex-, tissue-, and stage-specific transgene expression. As discussed in this review, information on the regulatory elements is available for mosquito vectors but is scant for other vectors.

Interactions between Leishmania parasite and sandfly: a review

Leishmaniasis transmission cycles are maintained and sustained in nature by the complex crosstalk of the Leishmania parasite, sandfly vector, and the mammalian hosts (human, as well as zoonotic reservoirs). Regardless of the vast research on human host-parasite interaction, there persists a substantial knowledge gap on the parasite's development and modulation in the vector component. This review focuses on some of the intriguing aspects of the Leishmania-sandfly interface, beginning with the uptake of the intracellular amastigotes from an infected host to the development of the parasite within the sandfly's alimentary canal, followed by the transmission of infective metacyclic stages to another potential host. Upon ingestion of the parasite, the sandfly hosts an intricate repertoire of immune barriers, either to evade the parasite or to ensure its homeostatic coexistence with the vector gut microbiome. Sandfly salivary polypeptides and Leishmania exosomes are co-egested with the parasite inoculum during the infected vector bite. This has been attributed to the modulation of the parasite infection and subsequent clinical manifestation in the host. While human host-based studies strive to develop effective therapeutics, a greater understanding of the vector-parasite-microbiome and human host interactions could help us to identify the targets and to develop strategies for effectively preventing the transmission of leishmaniasis.

Evidence of a conserved mammalian immunosuppression mechanism in Lutzomyia longipalpis upon infection with Leishmania

Introduction

Sand flies (Diptera: Phlebotominae) belonging to the Lutzomyia genus transmit Leishmania infantum parasites. To understand the complex interaction between the vector and the parasite, we have been investigating the sand fly immune responses during the Leishmania infection. Our previous studies showed that genes involved in the IMD, Toll, and Jak-STAT immunity pathways are regulated upon Leishmania and bacterial challenges. Nevertheless, the parasite can thrive in the vectors' gut, indicating the existence of mechanisms capable of modulating the vector defenses, as was already seen in mammalian Leishmania infections.

Methods results and discussion

In this study, we investigated the expression of Lutzomyia longipalpis genes involved in regulating the Toll pathway under parasitic infection. Leishmania infantum infection upregulated the expression of two L. longipalpis genes coding for the putative repressors cactus and protein tyrosine phosphatase SHP. These findings suggest that the parasite can modulate the vectors' immune response. In mammalian infections, the Leishmania surface glycoprotein GP63 is one of the inducers of host immune depression, and one of the known effectors is SHP. In L. longipalpis we found a similar effect: a genetically modified strain of Leishmania amazonensis over-expressing the metalloprotease GP63 induced a higher expression of the sand fly SHP indicating that the L. longipalpis SHP and parasite GP63 increased expressions are connected. Immuno-stained microscopy of L. longipalpis LL5 embryonic cells cultured with Leishmania strains or parasite conditioned medium showed cells internalization of parasite GP63. A similar internalization of GP63 was observed in the sand fly gut tissue after feeding on parasites, parasite exosomes, or parasite conditioned medium, indicating that GP63 can travel through cells in vitro or in vivo. When the sand fly SHP gene was silenced by RNAi and females infected by L. infantum, parasite loads decreased in the early phase of infection as expected, although no significant differences were seen in late infections of the stomodeal valve.

Conclusions

Our findings show the possible role of a pathway repressor involved in regulating the L. longipalpis immune response during Leishmania infections inside the insect. In addition, they point out a conserved immunosuppressive effect of GP63 between mammals and sand flies in the early stage of parasite infection.

CRISPR-Cas Technology as a Revolutionary Genome Editing tool: Mechanisms and Biomedical Applications

Programmable nucleases are powerful genomic tools for precise genome editing. These tools precisely recognize, remove, or change DNA at a defined site, thereby, stimulating cellular DNA repair pathways that can cause mutations or accurate replacement or deletion/insertion of a sequence. CRISPR-Cas9 system is the most potent and useful genome editing technique adapted from the defense immune system of certain bacteria and archaea against viruses and phages. In the past decade, this technology made notable progress, and at present, it has largely been used in genome manipulation to make precise gene editing in plants, animals, and human cells. In this review, we aim to explain the basic principle, mechanisms of action, and applications of this system in different areas of medicine, with emphasizing on the detection and treatment of parasitic diseases.

CRISPR-cas9 screening identified lethal genes enriched in Hippo kinase pathway and of predictive significance in primary low-grade glioma

BACKGROUND

Low-grade gliomas (LGG) are a type of brain tumor that can be lethal, and it is essential to identify genes that are correlated with patient prognosis. In this study, we aimed to use CRISPR-cas9 screening data to identify key signaling pathways and develop a genetic signature associated with high-risk, low-grade glioma patients.

METHODS

The study used CRISPR-cas9 screening data to identify essential genes correlated with cell survival in LGG. We used RNA-seq data to identify differentially expressed genes (DEGs) related to cell viability. Moreover, we used the least absolute shrinkage and selection operator (LASSO) method to construct a genetic signature for predicting overall survival in patients. We performed enrichment analysis to identify pathways mediated by DEGs, overlapping genes, and genes shared in the Weighted correlation network analysis (WGCNA). Finally, the study used western blot, qRT-PCR, and IHC to detect the expression of hub genes from signature in clinical samples.

RESULTS

The study identified 145 overexpressed oncogenes in low-grade gliomas using the TCGA database. These genes were intersected with lethal genes identified in the CRISPR-cas9 screening data from Depmap database, which are enriched in Hippo pathways. A total of 19 genes were used to construct a genetic signature, and the Hippo signaling pathway was found to be the predominantly enriched pathway. The signature effectively distinguished between low- and high-risk patients, with high-risk patients showing a shorter overall survival duration. Differences in hub gene expression were found in different clinical samples, with the protein and mRNA expression of REP65 being significantly up-regulated in tumor cells. The study suggests that the Hippo signaling pathway may be a critical regulator of viability and tumor proliferation and therefore is an innovative new target for treating cancerous brain tumors, including low-grade gliomas.

CONCLUSION

Our study identified a novel genetic signature associated with high-risk, LGG patients. We found that the Hippo signaling pathway was significantly enriched in this signature, indicating that it may be a critical regulator of tumor viability and proliferation in LGG. Targeting the Hippo pathway could be an innovative new strategy for treating LGG.

RNAi-mediated gene silencing of Phlebotomus papatasi defensins favors Leishmania major infection

Introduction: Production of different antimicrobial peptides (AMPs) is one of the insect's prominent defense strategies, regulated mainly by Toll and immune deficiency (IMD) humoral pathways. Here we focused mainly on two AMPs of Phlebotomus papatasi, vector of Leishmania major parasites, their association with the relish transcription factor and the effective participation on Leishmania infection. Methods and results: We further characterized the role of previously described gut-specific P. papatasi defensin (PpDef1) and identified the second defensin (PpDef2) expressed in various sand fly tissues. Using the RNAi-mediated gene silencing, we report that the silencing of PpDef1 gene or simultaneous silencing of both defensin genes (PpDef1 and PpDef2) resulted in increased parasite levels in the sand fly (detectable by PCR) and higher sand fly mortality. In addition, we knocked down relish, the sole transcription factor of the IMD pathway, to evaluate the association of the IMD pathway with AMPs expression in P. papatasi. We demonstrated that the relish gene knockdown reduced the expression of PpDef2 and attacin, another AMP abundantly expressed in the sand fly body. Conclusions: Altogether, our experiments show the importance of defensins in the sand fly response toward L. major and the role of the IMD pathway in regulating AMPs in P. papatasi.

Genomic analysis of two phlebotomine sand fly vectors of Leishmania from the New and Old World

Phlebotomine sand flies are of global significance as important vectors of human disease, transmitting bacterial, viral, and protozoan pathogens, including the kinetoplastid parasites of the genus Leishmania, the causative agents of devastating diseases collectively termed leishmaniasis. More than 40 pathogenic Leishmania species are transmitted to humans by approximately 35 sand fly species in 98 countries with hundreds of millions of people at risk around the world. No approved efficacious vaccine exists for leishmaniasis and available therapeutic drugs are either toxic and/or expensive, or the parasites are becoming resistant to the more recently developed drugs. Therefore, sand fly and/or reservoir control are currently the most effective strategies to break transmission. To better understand the biology of sand flies, including the mechanisms involved in their vectorial capacity, insecticide resistance, and population structures we sequenced the genomes of two geographically widespread and important sand fly vector species: Phlebotomus papatasi, a vector of Leishmania parasites that cause cutaneous leishmaniasis, (distributed in Europe, the Middle East and North Africa) and Lutzomyia longipalpis, a vector of Leishmania parasites that cause visceral leishmaniasis (distributed across Central and South America). We categorized and curated genes involved in processes important to their roles as disease vectors, including chemosensation, blood feeding, circadian rhythm, immunity, and detoxification, as well as mobile genetic elements. We also defined gene orthology and observed micro-synteny among the genomes. Finally, we present the genetic diversity and population structure of these species in their respective geographical areas. These genomes will be a foundation on which to base future efforts to prevent vector-borne transmission of Leishmania parasites.

Leishmania allelic selection during experimental sand fly infection correlates with mutational signatures of oxidative DNA damage

Trypanosomatid pathogens are transmitted by blood-feeding insects, causing devastating human infections. These parasites show important phenotypic shifts that often impact parasite pathogenicity, tissue tropism, or drug susceptibility. The evolutionary mechanisms that allow for the selection of such adaptive phenotypes remain only poorly investigated. Here, we use Leishmania donovani as a trypanosomatid model pathogen to assess parasite evolutionary adaptation during experimental sand fly infection. Comparing the genome of the parasites before and after sand fly infection revealed a strong population bottleneck effect as judged by allele frequency analysis. Apart from random genetic drift caused by the bottleneck effect, our analyses revealed haplotype and allelic changes during sand fly infection that seem under natural selection given their convergence between independent biological replicates. Our analyses further uncovered signature mutations of oxidative DNA damage in the parasite genomes after sand fly infection, suggesting that Leishmania suffers from oxidative stress inside the insect digestive tract. Our results propose a model of Leishmania genomic adaptation during sand fly infection, with oxidative DNA damage and DNA repair processes likely driving haplotype and allelic selection. The experimental and computational framework presented here provides a useful blueprint to assess evolutionary adaptation of other eukaryotic pathogens inside their insect vectors, such as Plasmodium spp, Trypanosoma brucei, and Trypanosoma cruzi.

A perspective on the expansion of the genetic technologies to support the control of neglected vector-borne diseases and conservation

Genetic-based technologies are emerging as promising tools to support vector population control. Vectors of human malaria and dengue have been the main focus of these development efforts, but in recent years these technologies have become more flexible and adaptable and may therefore have more wide-ranging applications. Culex quinquefasciatus, for example, is the primary vector of avian malaria in Hawaii and other tropical islands. Avian malaria has led to the extinction of numerous native bird species and many native bird species continue to be threatened as climate change is expanding the range of this mosquito. Genetic-based technologies would be ideal to support avian malaria control as they would offer alternatives to interventions that are difficult to implement in natural areas, such as larval source reduction, and limit the need for chemical insecticides, which can harm beneficial species in these natural areas. This mosquito is also an important vector of human diseases, such as West Nile and Saint Louis encephalitis viruses, so genetic-based control efforts for this species could also have a direct impact on human health. This commentary will discuss the current state of development and future needs for genetic-based technologies in lesser studied, but important disease vectors, such as C. quinquefasciatus, and make comparisons to technologies available in more studied vectors. While most current genetic control focuses on human disease, we will address the impact that these technologies could have on both disease and conservation focused vector control efforts and what is needed to prepare these technologies for evaluation in the field. The versatility of genetic-based technologies may result in the development of many important tools to control a variety of vectors that impact human, animal, and ecosystem health.

Host-Parasite Interactions: Regulation of Leishmania Infection in Sand Fly

PURPOSE

Sand flies are the only proven vectors of leishmaniases, a tropical neglected disease endemic in at least 92 countries. Vector-parasite interactions play a significant role in vector-borne disease transmission. There are various bottlenecks to Leishmania colonization of the sand fly midgut. Such bottlenecks include the production of innate immune-related molecules, digestive proteases, parasite impermeable peritrophic membrane, and resident gut microbiota. These barriers determine the parasite load transmitted and, consequently, the disease outcome in mammalian host. Therefore, it is important to understand the molecular responses of both sand fly and Leishmania during infection.

METHOD

Here, we reviewed the published literature on sand fly-Leishmania interactions bringing together earlier and current findings to highlight new developments and research gaps in the field.

CONCLUSION

Recent research studies on sand fly-Leishmania interaction have revealed contrasting observations to past studies. However, how Leishmania parasites evade the sand fly immune response still needs further research. Sand fly response to Leishmania infection can be best understood by analyzing its tissue transcriptome. Better characterization of the role of midgut components could be a game changer in development of transmission-blocking strategies for leishmaniasis.

Phlebotomus papatasi Antimicrobial Peptides in Larvae and Females and a Gut-Specific Defensin Upregulated by Leishmania major Infection

Phlebotomus papatasi is the vector of Leishmania major, causing cutaneous leishmaniasis in the Old World. We investigated whether P. papatasi immunity genes were expressed toward L. major, commensal gut microbes, or a combination of both. We focused on sand fly transcription factors dorsal and relish and antimicrobial peptides (AMPs) attacin and defensin and assessed their relative gene expression by qPCR. Sand fly larvae were fed food with different bacterial loads. Relish and AMPs gene expressions were higher in L3 and early L4 larval instars, while bacteria 16S rRNA increased in late L4 larval instar, all fed rich-microbe food compared to the control group fed autoclaved food. Sand fly females were treated with an antibiotic cocktail to deplete gut bacteria and were experimentally infected by Leishmania. Compared to non-infected females, dorsal and defensin were upregulated at early and late infection stages, respectively. An earlier increase of defensin was observed in infected females when bacteria recolonized the gut after the removal of antibiotics. Interestingly, this defensin gene expression occurred specifically in midguts but not in other tissues of females and larvae. A gut-specific defensin gene upregulated by L. major infection, in combination with gut-bacteria, is a promising molecular target for parasite control strategies.

Aedes aegypti Infection With Trypanosomatid Strigomonas culicis Alters Midgut Redox Metabolism and Reduces Mosquito Reproductive Fitness

Aedes aegypti mosquitoes transmit arboviruses of important global health impact, and their intestinal microbiota can influence vector competence by stimulating the innate immune system. Midgut epithelial cells also produce toxic reactive oxygen species (ROS) by dual oxidases (DUOXs) that are essential players in insect immunity. Strigomonas culicis is a monoxenous trypanosomatid that naturally inhabits mosquitoes; it hosts an endosymbiotic bacterium that completes essential biosynthetic pathways of the parasite and influences its oxidative metabolism. Our group previously showed that S. culicis hydrogen peroxide (H₂O₂)-resistant (WTR) strain is more infectious to A. aegypti mosquitoes than the wild-type (WT) strain. Here, we investigated the influence of both strains on the midgut oxidative environment and the effect of infection on mosquito fitness and immunity. WT stimulated the production of superoxide by mitochondrial metabolism of midgut epithelial cells after 4 days post-infection, while WTR exacerbated H₂O₂ production mediated by increased DUOX activity and impairment of antioxidant system. The infection with both strains also disrupted the fecundity and fertility of the females, with a greater impact on reproductive fitness of WTR-infected mosquitoes. The presence of these parasites induced specific transcriptional modulation of immune-related genes, such as attacin and defensin A during WTR infection (11.8- and 6.4-fold, respectively) and defensin C in WT infection (7.1-fold). Thus, we propose that A. aegypti oxidative response starts in early infection time and does not affect the survival of the H₂O₂-resistant strain, which has a more efficient antioxidant system. Our data provide new biological aspects of A. aegypti–S. culicis relationship that can be used later in alternative vector control strategies.

Chemical control and insecticide resistance status of sand fly vectors worldwide

BACKGROUND

Phlebotomine sand flies are prominent vectors of Leishmania parasites that cause leishmaniasis, which comes second to malaria in terms of parasitic causative fatalities globally. In the absence of human vaccines, sand fly chemical-based vector control is a key component of leishmaniasis control efforts.

METHODS AND FINDINGS

We performed a literature review on the current interventions, primarily, insecticide-based used for sand fly control, as well as the global insecticide resistance (IR) status of the main sand fly vector species. Indoor insecticidal interventions, such as residual spraying and treated bed nets are the most widely deployed, while several alternative control strategies are also used in certain settings and/or are under evaluation. IR has been sporadically detected in sand flies in India and other regions, using non-standardized diagnostic bioassays. Molecular studies are limited to monitoring of known pyrethroid resistance mutations (kdr), which are present at high frequencies in certain regions.

CONCLUSIONS

As the leishmaniasis burden remains a major problem at a global scale, evidence-based rational use of insecticidal interventions is required to meet public health demands. Standardized bioassays and molecular markers are a prerequisite for this task, albeit are lagging behind. Experiences from other disease vectors underscore the need for the implementation of appropriate IR management (IRM) programs, in the framework of integrated vector management (IVM). The implementation of alternative strategies seems context- and case-specific, with key eco-epidemiological parameters yet to be investigated. New biotechnology-based control approaches might also come into play in the near future to further reinforce sand fly/leishmaniasis control efforts.

Towards a Sustainable Vector-Control Strategy in the Post Kala-Azar Elimination Era

Visceral leishmaniasis (VL) is a potentially deadly parasitic disease. In the Indian sub-continent, VL is caused by Leishmania donovani and transmitted via the bite of an infected Phlebotomus argentipes female sand fly, the only competent vector species in the region. The highest disease burden is in the northern part of the Indian sub-continent, especially in the state of Bihar. India, Bangladesh, and Nepal embarked on an initiative, coordinated by World Health Organization, to eliminate VL as a public health problem by the year 2020. The main goal is to reduce VL incidence below one case per 10,000 people through early case-detection, prompt diagnosis and treatment, and reduction of transmission using vector control measures. Indoor residual spraying, a major pillar of the elimination program, is the only vector control strategy used by the government of India. Though India is close to its VL elimination target, important aspects of vector bionomics and sand fly transmission dynamics are yet to be determined. To achieve sustained elimination and to prevent a resurgence of VL, knowledge gaps in vector biology and behavior, and the constraints they may pose to current vector control methods, need to be addressed. Herein, we discuss the successes and failures of previous and current vector-control strategies implemented to combat kala-azar in Bihar, India, and identify gaps in our understanding of vector transmission towards development of innovative tools to ensure sustained vector control in the post-elimination period.

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.

Modulation of IMD, Toll, and Jak/STAT Immune Pathways Genes in the Fat Body of Rhodnius prolixus During Trypanosoma rangeli Infection

Trypanosoma rangeli is the second most common American trypanosome that infects man. It is vectored by triatomines from the genus Rhodnius, in which it invades the hemolymph and infects the salivary glands, avoiding the bug immune responses. In insects, these responses are initiated by well conserved pathways, mainly the IMD, Toll, and Jak/STAT. We hypothesize that long-term infection with T. rangeli in the gut or hemolymph of Rhodnius prolixus triggers different systemic immune responses, which influence the number of parasites that survive inside the vector. Thus, we investigated groups of insects with infections in the gut and/or hemolymph, and evaluated the parasite load and the expression in the fat body of transcription factors (Rp-Relish, Rp-Dorsal, and Rp-STAT) and inhibitors (Rp-Cactus and Rp-Caspar) of the IMD, Toll, and Jak/STAT pathways. We detected lower parasite counts in the gut of insects without hemolymph infection, compared to hemolymph-infected groups. Besides, we measured higher parasite numbers in the gut of bugs that were first inoculated with T. rangeli and then fed on infected mice, compared with control insects, indicating that hemolymph infection increases parasite numbers in the gut. Interestingly, we observed that genes from the three immune pathways where differentially modulated, depending on the region parasites were present, as we found (1) Rp-Relish downregulated in gut-and/or-hemolymph-infected insects, compared with controls; (2) Rp-Cactus upregulated in gut-infected insect, compared with controls and gut-and-hemolymph-infected groups; and (3) Rp-STAT downregulated in all groups of hemolymph-infected insects. Finally, we uncovered negative correlations between parasite loads in the gut and Rp-Relish and Rp-Cactus expression, and between parasite counts in the hemolymph and Rp-Relish levels, suggesting an association between parasite numbers and the IMD and Toll pathways. Overall, our findings reveal new players in R. prolixus-T. rangeli interactions that could be key for the capacity of the bug to transmit the pathogen.

Sand Fly Studies Predict Transmission Potential of Drug-resistant Leishmania

Leishmania parasites have the capacity to rapidly adapt to changing environments in their digenetic life cycle which alternates between a vertebrate and an invertebrate host. Emergence of resistance following drug exposure can evoke phenotypic alterations that affect several aspects of parasite fitness in both hosts. Current studies of the impact of resistance are mostly limited to interactions with the mammalian host and characterization of in vitro parasite growth and differentiation. Development in the vector and transmission capacity have been largely ignored. This review reflects on the impact of drug resistance on its spreading potential with specific focus on the use of the sand fly infection model to evaluate parasite development in the vector and the ensuing transmission potential of drug-resistant phenotypes.