The JAK-STAT pathway controls Plasmodium vivax load in early stages of Anopheles aquasalis infection

Gene expression analysis of Anopheles Meigen, 1818 (Diptera: Culicidae) innate immunity after Plasmodium Marchiafava & Celli, 1885 (Apicomplexa) infection: Toward developing new malaria control strategies

Despite the critical role of the Anopheles innate immune system in defending against Plasmodium infection, there is still limited information about the key immune mechanisms in Anopheles. This review assesses recent findings on the expression characteristics of immune-related genes in Anopheles following exposure to Plasmodium. A literature review, unrestricted by publication date, was conducted to evaluate immune-related gene expression in different organs of Anopheles after Plasmodium infection. Mosquito immune responses in the midgut are essential for reducing parasite populations. Additionally, innate immune responses in the salivary glands and hemocytes circulating in the hemocoel play key roles in defense against the parasite. Transcriptomic analysis of the mosquito's innate immune response to Plasmodium infection provides valuable insights into key immune mechanisms in mosquito defense. A deeper understanding of immune mechanisms in different organs of Anopheles following Plasmodium infection will aid in discovering critical targets for designing novel control strategies.

Curing mosquitoes with genetic approaches for malaria control

Malaria remains a persistent global public health challenge because of the limitations of current prevention tools. The use of transgenic mosquitoes incapable of transmitting malaria, in conjunction with existing methods, holds promise for achieving elimination of malaria and preventing its reintroduction. In this context, population modification involves the spread of engineered genetic elements through mosquito populations that render them incapable of malaria transmission. Significant progress has been made in this field over the past decade in revealing promising targets, optimizing genetic tools, and facilitating the transition from the laboratory to successful field deployments, which are subject to regulatory scrutiny. This review summarizes recent advances and ongoing challenges in 'curing' Anopheles vectors of the malaria parasite.

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway contributes to the defense against bacterial infection in the pea aphid

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling is activated by infections of bacteria, fungi, viruses and parasites and mediated cellular and humoral immune responses. In the pea aphid Acyrthosiphon pisum little is known about the function of JAK/STAT signaling in its immune system. In this study, we first showed that expression of genes in the JAK/STAT signaling, including the receptors Domeless1/2, Janus kinase (JAK) and transcriptional factor Stat92E, is up-regulated upon bacteria Escherichia coli and Staphylococcus aureus and fungus Beauveria bassiana infections. After knockdown of expression of these genes by means of dsRNA injection, the aphids harbored more bacteria and suffered more death after infected with E. coli and S. aureus, but showed no significant change after B. bassiana infection. Our study suggests the JAK/STAT signaling contributes to the defense against bacterial infection in the pea aphid.

Response of the mosquito immune system and symbiotic bacteria to pathogen infection

Mosquitoes are the deadliest animal in the word, transmitting a variety of insect-borne infectious diseases, such as malaria, dengue fever, yellow fever, and Zika, causing more deaths than any other vector-borne pathogen. Moreover, in the absence of effective drugs and vaccines to prevent and treat insect-borne diseases, mosquito control is particularly important as the primary measure. In recent decades, due to the gradual increase in mosquito resistance, increasing attention has fallen on the mechanisms and effects associated with pathogen infection. This review provides an overview of mosquito innate immune mechanisms in terms of physical and physiological barriers, pattern recognition receptors, signalling pathways, and cellular and humoral immunity, as well as the antipathogenic effects of mosquito symbiotic bacteria. This review contributes to an in-depth understanding of the interaction process between mosquitoes and pathogens and provides a theoretical basis for biological defence strategies against mosquito-borne infectious diseases.

Unravelling the genome of the brackish water malaria vector Anopheles aquasalis

Malaria is a severe public health problem in several developing tropical and subtropical countries. Anopheles aquasalis is the primary coastal malaria vector in Central and South America and the Caribbean Islands, and it has the peculiar feature of living in water with large changes in salinity. Recent research has recognised An. aquasalis as an important model for studying the interactions of murine and human Plasmodium parasites. This study presents the complete genome of An. aquasalis and offers insights into its evolution and physiology. The genome is similar in size and gene content to other Neotropical anophelines, with 162 Mb and 12,446 protein-coding genes. There are 1387 single-copy orthologs at the Diptera level (eg. An. gambiae, An. darlingi and Drosophila melanogaster). An. aquasalis diverged from An. darlingi, the primary malaria vector in inland South America, nearly 20 million years ago. Proteins related to ion transport and metabolism belong to the most abundant gene families with 660 genes. We identified gene families relevant to osmosis control (e.g., aquaporins, vacuolar-ATPases, Na+/K+-ATPases, and carbonic anhydrases). Evolutionary analysis suggests that all osmotic regulation genes are under strong purifying selection. We also observed low copy number variation in insecticide resistance and immunity-related genes for all known classical pathways. The data provided by this study offers candidate genes for further studies of parasite-vector interactions and for studies on how anophelines of brackish water deal with the high fluctuation in water salinity. We also established data and insights supporting An. aquasalis as an emerging Neotropical malaria vector model for genetic and molecular studies.

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.

Evolution and assembly of Anopheles aquasalis's immune genes: primary malaria vector of coastal Central and South America and the Caribbean Islands

Anophelines are vectors of malaria, the deadliest disease worldwide transmitted by mosquitoes. The availability of genomic data from various Anopheles species allowed evolutionary comparisons of the immune response genes in search of alternative vector control of the malarial parasites. Now, with the Anopheles aquasalis genome, it was possible to obtain more information about the evolution of the immune response genes. Anopheles aquasalis has 278 immune genes in 24 families or groups. Comparatively, the American anophelines possess fewer genes than Anopheles gambiae s. s., the most dangerous African vector. The most remarkable differences were found in the pathogen recognition and modulation families like FREPs, CLIP and C-type lectins. Even so, genes related to the modulation of the expression of effectors in response to pathogens and gene families that control the production of reactive oxygen species were more conserved. Overall, the results show a variable pattern of evolution in the immune response genes in the anopheline species. Environmental factors, such as exposure to different pathogens and differences in the microbiota composition, could shape the expression of this group of genes. The results presented here will contribute to a better knowledge of the Neotropical vector and open opportunities for malaria control in the endemic-affected areas of the New World.

Rift Valley Fever Virus Primes Immune Responses in Aedes aegypti Cells

The ongoing global emergence of arthropod-borne (arbo) viruses has accelerated research into the interactions of these viruses with the immune systems of their vectors. Only limited information exists on how bunyaviruses, such as Rift Valley fever virus (RVFV), are sensed by mosquito immunity or escape detection. RVFV is a zoonotic phlebovirus (Bunyavirales; Phenuiviridae) of veterinary and human public health and economic importance. We have shown that the infection of mosquitoes with RVFV triggers the activation of RNA interference pathways, which moderately restrict viral replication. Here, we aimed to better understand the interactions between RVFV and other vector immune signaling pathways that might influence RVFV replication and transmission. For this, we used the immunocompetent Aedes aegypti Aag2 cell line as a model. We found that bacteria-induced immune responses restricted RVFV replication. However, virus infection alone did not alter the gene expression levels of immune effectors. Instead, it resulted in the marked enhancement of immune responses to subsequent bacterial stimulation. The gene expression levels of several mosquito immune pattern recognition receptors were altered by RVFV infection, which may contribute to this immune priming. Our findings imply that there is a complex interplay between RVFV and mosquito immunity that could be targeted in disease prevention strategies.

Amazonian Anopheles with low numbers of oocysts transmit Plasmodium vivax sporozoites during a blood meal

Anopheles darlingi is the main malarial vector in the Brazilian Amazon region. An. nuneztovari s.l., An. triannulatus s.l., An. evansae, and An. benarrochi s.l. do not have a defined role as malarial vectors, although they have been found to be naturally infected with Plasmodium vivax, and some develop oocysts. In this study, we evaluated the importance of low numbers of oocysts in sporozoite salivary gland invasion and transmission. Field-collected mosquitoes were experimentally infected with P. vivax. The infection rates and oocyst and sporozoite infection intensities were evaluated and compared with those of An. aquasalis. We found the highest number of oocysts in An. darlingi (mean = 39.47) and the lowest in An. nuneztovari s.l. (mean = 2). The highest number of sporozoites was observed in An. darlingi (mean = 610) and lowest in An. benarrochi s.l. (mean = 30). Plasmodium vivax DNA was detected in the saliva of all mosquito species after a blood meal. Regardless of the number of oocysts, all species transmitted sporozoites during blood meals. Considering the abundance of these mosquitoes and transmission of sporozoites, it is logical to assume that An. nuneztovari s.l. and An. triannulatus s.l. are involved in the transmission of P. vivax.

The immune deficiency and c-Jun N-terminal kinase pathways drive the functional integration of the immune and circulatory systems of mosquitoes

The immune and circulatory systems of animals are functionally integrated. In mammals, the spleen and lymph nodes filter and destroy microbes circulating in the blood and lymph, respectively. In insects, immune cells that surround the heart valves (ostia), called periostial haemocytes, destroy pathogens in the areas of the body that experience the swiftest haemolymph (blood) flow. An infection recruits additional periostial haemocytes, amplifying heart-associated immune responses. Although the structural mechanics of periostial haemocyte aggregation have been defined, the genetic factors that regulate this process remain less understood. Here, we conducted RNA sequencing in the African malaria mosquito, Anopheles gambiae, and discovered that an infection upregulates multiple components of the immune deficiency (IMD) and c-Jun N-terminal kinase (JNK) pathways in the heart with periostial haemocytes. This upregulation is greater in the heart with periostial haemocytes than in the circulating haemocytes or the entire abdomen. RNA interference-based knockdown then showed that the IMD and JNK pathways drive periostial haemocyte aggregation and alter phagocytosis and melanization on the heart, thereby demonstrating that these pathways regulate the functional integration between the immune and circulatory systems. Understanding how insects fight infection lays the foundation for novel strategies that could protect beneficial insects and harm detrimental ones.

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.

Sexual Dimorphism in Immune Responses and Infection Resistance in Aedes aegypti and Other Hematophagous Insect Vectors

Sexual dimorphism in immune function is prevalent across different species, where males trade their ability to fight pathogens for a practical reproductive function while females favor an extended lifespan. In insects, these differences in immune function reflect an evolutionary life strategy, where females have a presumably more robust immune system than insect males. Here, we evaluate immune functioning in four male and female insect vectors, Aedes aegypti (Diptera, Culicidae), Anopheles aquasalis (Diptera, Culicidae), Lutzomyia longipalpis (Diptera, Psychodidae) and Rhodnius prolixus (Hemiptera, Reduviidae). We show evidence that challenges the concept of immune sexual dimorphism in three of these insect vectors. In the three Diptera species, A. aegypti, A. aquasalis and L. longipalpis that transmit arboviruses, Plasmodium spp. (Haemospororida, Plasmodiidae) and Leishmania spp. (Trypanosomatida, Trypanosomatidae), respectively, unchallenged adult males express higher levels of immune-related genes than adult females and immature developmental stages. The main components of the Toll, IMD, and Jak/STAT pathways and antimicrobial effectors are highly expressed in whole-body males. Additionally, males present lower midgut basal microbiota levels than females. In A. aegypti mosquitoes, the differences in immune gene expression and microbiota levels are established in adult mosquitoes but are not present at the recently emerged adults and pupal stage. Antibiotic treatment does not affect the consistently higher expression of immune genes in males, except defensin, which is reduced significantly after microbiota depletion and restored after re-introduction. Our data suggest that Diptera males have a basal state of activation of the immune system and that activation of a more robust response through systemic immune challenge acutely compromises their survival. The ones who survive clear the infection entirely. Females follow a different strategy where a moderate immune reaction render higher tolerance to infection and survival. In contrast, hematophagous adult males of the Hemiptera vector R. prolixus, which transmits Trypanosoma cruzi, present no differences in immune activation compared to females, suggesting that diet differences between males and females may influence immune sexual dimorphism. These findings expand our understanding of the biology of insect vectors of human pathogens, which can help to direct the development of new strategies to limit vector populations.

Nitric Oxide Synthase Regulates Gut Microbiota Homeostasis by ERK-NF-κB Pathway in Shrimp

The gut microbiota is a complex group of microorganisms that is not only closely related to intestinal immunity but also affects the whole immune system of the body. Antimicrobial peptides and reactive oxygen species participate in the regulation of gut microbiota homeostasis in invertebrates. However, it is unclear whether nitric oxide, as a key mediator of immunity that plays important roles in antipathogen activity and immune regulation, participates in the regulation of gut microbiota homeostasis. In this study, we identified a nitric oxide synthase responsible for NO production in the shrimp Marsupenaeus japonicus. The expression of Nos and the NO concentration in the gastrointestinal tract were increased significantly in shrimp orally infected with Vibrio anguillarum. After RNA interference of Nos or treatment with an inhibitor of NOS, L-NMMA, NO production decreased and the gut bacterial load increased significantly in shrimp. Treatment with the NO donor, sodium nitroprusside, increased the NO level and reduced the bacterial load significantly in the shrimp gastrointestinal tract. Mechanistically, V. anguillarum infection increased NO level via upregulation of NOS and induced phosphorylation of ERK. The activated ERK phosphorylated the NF-κB-like transcription factor, dorsal, and caused nuclear translocation of dorsal to increase expression of antimicrobial peptides (AMPs) responsible for bacterial clearance. In summary, as a signaling molecule, NOS-produced NO regulates intestinal microbiota homeostasis by promoting AMP expression against infected pathogens via the ERK-dorsal pathway in shrimp.

Leishmania infantum Infection Modulates the Jak-STAT Pathway in Lutzomyia longipalpis LL5 Embryonic Cells and Adult Females, and Affects Parasite Growth in the Sand Fly

Phlebotomine sand flies (Diptera, Psychodidae) belonging to the Lutzomyia genus transmit zoonoses in the New World. Lutzomyia longipalpis is the main vector of Leishmania infantum, which is the causative agent of visceral leishmaniasis in Brazil. To identify key molecular aspects involved in the interaction between vector and pathogens and contribute to developing disease transmission controls, we investigated the sand fly innate immunity mediated by the Janus kinase/signal transducer and activator of transcription (Jak-STAT) pathway in response to L. infantum infection. We used two study models: L. longipalpis LL5 embryonic cells co-cultured with L. infantum and sand fly females artificially infected with the parasite. We used qPCR to follow the L. longipalpis gene expression of molecules involved in the Jak-STAT pathway. Also, we modulated the Jak-STAT mediated immune response to understand its role in Leishmania parasite infection. For that, we used RNAi to silence the pathway regulators, protein inhibitor of activated STATs (PIAS) in LL5 cells, and STAT in adult females. In addition, the pathway suppression effect on parasite development within the vector was assessed by light microscopy in late-phase infection. The silencing of the repressor PIAS in LL5 cells led to a moderate increase in a protein tyrosine phosphatase 61F (PTP61F) expression. It suggests a compensatory regulation between these two repressors. L. infantum co-culture with LL5 cells upregulated repressors PIAS, suppressor of cytokine signaling (SOCS), and PTP61F. It also downmodulated virus-induced RNA-1 (VIR-1), a pathway effector, indicating that the parasite could repress the Jak-STAT pathway in LL5 cells. In Leishmania-infected L. longipalpis females, STAT and the antimicrobial peptide attacin were downregulated on the third day post-infection, suggesting a correlation that favors the parasite survival at the end of blood digestion in the sand fly. The antibiotic treatment of infected females showed that the reduction of gut bacteria had little effect on the Jak-STAT pathway regulation. STAT gene silencing mediated by RNAi reduced the expression of inducible nitric oxide synthase (iNOS) and favored Leishmania growth in sand flies on the first day post-infection. These results indicate that STAT participated in the iNOS regulation with subsequent effect on parasite survival.

Phenotypic traits of individuals in a long-term colony of Anopheles (Nyssorhynchus) aquasalis (Diptera: Culicidae) show variable susceptibility to Plasmodium and suggest cryptic speciation

Anopheles aquasalis is an important malaria vector in coastal regions of South America and islands of the Caribbean. In its original description, the species was divided into two varieties, based on the scaling patterns of their hind-tarsomere 2. Specimens from our 25-year established colony, used for Plasmodium experimental infections, still exhibit both scaling tarsomere patterns. This study examined the DNA sequence of the nuclear Internal Transcribed Spacer 2 (ITS2) and susceptibility to Plasmodium, looking for differences among the phenotypes 30BS and 50BS. One hundred mosquitoes, 25 males and 25 females of each sex, and phenotype were analyzed. Twenty-seven novel haplotypes were identified. Three were found in both phenotypes (30BS and 50BS) regardless of gender. Among the other 27 genotypes, we observed a male-oriented bias in both phenotypic categories. Evaluation of Plasmodium yoelii N67 infections, based on oocyst counts, showed a higher susceptibility of 30BS compared with 50BS. Future studies need to be conducted to evaluate if these genotype assortments among the phenotypic groups reflect differences in fitness, mating, and their susceptibility to infection by Plasmodium parasites.

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.

Diversity of midgut bacteria in larvae and females of Aedes aegypti and Aedes albopictus from Gampaha District, Sri Lanka

BACKGROUND

The midgut microbiota of mosquitoes maintain basal immune activity and immune priming. In recent years, scientists have focused on the use of microbial communities for vector control interventions. In the present study, the midgut bacteria of larvae and adults of Aedes aegypti and Ae. albopictus were assessed using both field-collected and laboratory-reared mosquitoes from Sri Lanka.

METHODS

Adults and larvae of Ae. aegypti and Ae. albopictus were collected from three selected areas in Gampaha Medical Officer of Health area, Gampaha District, Western Province, Sri Lanka. Bacterial colonies isolated from mosquito midgut dissections were identified by PCR amplification and sequencing of partial 16S rRNA gene fragments.

RESULTS

Adults and larvae of Ae. aegypti and Ae. albopictus harbored 25 bacterial species. Bacillus endophyticus and Pantoea dispersa were found more frequently in field-collected Ae. aegypti and Ae. albopictus adults, respectively. The midgut bacteria of Ae. aegypti and Ae. albopictus adults (X² = 556.167, df = 72, P < 0.001) and larvae (X² = 633.11, df = 66, P < 0.001) were significantly different. There was a significant difference among the bacterial communities between field-collected adults (X² = 48.974, df = 10, P < 0.001) and larvae (X² = 84.981, df = 10, P < 0.001). Lysinibacillus sphaericus was a common species in adults and larvae of laboratory-reared Ae. aegypti. Only P. dispersa occurred in the field-collected adults of Ae. aegypti and Ae. albopictus. Species belonging to genera Terribacillus, Lysinibacillus, Agromyces and Kocuria were recorded from Aedes mosquitoes, in accordance with previously reported results.

CONCLUSIONS

This study generated a comprehensive database on the culturable bacterial community found in the midgut of field-collected (Ae. aegypti and Ae. albopictus) and laboratory-reared (Ae. aegypti) mosquito larvae and adults from Sri Lanka. Data confirm that the midgut bacterial diversity in the studied mosquitoes varies according to species, developmental stage and strain (field vs laboratory).

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.

Bacillus sphaericus exposure reduced vector competence of Anopheles dirus to Plasmodium yoelii by upregulating the Imd signaling pathway

Background

Vector control with Bacillus sphaericus (Bs) is an effective way to block the transmission of malaria. However, in practical application of Bs agents, a sublethal dose effect was often caused by insufficient dosing, and it is little known whether the Bs exposure would affect the surviving mosquitoes’ vector capacity to malaria.

Methods

A sublethal dose of the Bs 2362 strain was administrated to the early fourth-instar larvae of Anopheles dirus to simulate shortage use of Bs in field circumstance. To determine vector competence, mosquitoes were dissected and the oocysts in the midguts were examined on day 9–11 post-infection with Plasmodium yoelii. Meanwhile, a SYBR quantitative PCR assay was conducted to examine the transcriptional level of the key immune molecules of mosquitoes, and RNA interference was utilized to validate the role of key immune effector molecule TEP1.

Results

The sublethal dose of Bs treatment significantly reduced susceptibility of An. dirus to P. yoelii, with the decrease of P. yoelii infection intensity and rate. Although there existed a melanization response of adult An. dirus following challenge with P. yoelii, it was not involved in the decrease of vector competence as no significant difference of melanization rates and densities between the control and Bs groups was found. Further studies showed that Bs treatment significantly increased TEP1 expression in the fourth-instar larvae (L4), pupae (Pu), 48 h post-infection (hpi) and 72 hpi (P < 0.001). Further, gene-silencing of TEP1 resulted in disappearance of the Bs impact on vector competence of An. dirus to P. yoelii. Moreover, the transcriptional level of PGRP-LC and Rel2 were significantly elevated by Bs treatment with decreased expression of the negative regulator Caspar at 48 hpi, which implied that the Imd signaling pathway was upregulated by Bs exposure.

Conclusions

Bs exposure can reduce the vector competence of An. dirus to malaria parasites through upregulating Imd signaling pathway and enhancing the expression of TEP1. The data could not only help us to understand the impact and mechanism of Bs exposure on Anopheles’ vector competence to malaria but also provide us with novel clues for wiping out malaria using vector control.

Composition and structure of the culturable gut bacterial communities in Anopheles albimanus from Colombia

The understanding of factors affecting the gut bacterial communities in malaria vectors is essential for the design of vector control interventions, such as those based on a paratransgenic approach. One of the requirements of this method is the availability of bacteria from the mosquito susceptible to culture. Thus, the aim of this study was to evaluate the composition and structure of the culturable gut bacterial communities in field mosquitoes Anopheles albimanus from Colombia, in addition to generate a bacterial collection to further analyze microbial functional activity. Gut bacteria were isolated from An. albimanus larvae and adult mosquitoes collected in localities of the Atlantic and Pacific Coasts. The bacterial isolates were grouped in 28 morphospecies that corresponded to three phyla, three classes, nine families and 14 genera. The larvae guts from San Antero (Atlantic Coast) and Buenaventura (Pacific Coast) shared the genera Bacillus and Lysinibacillus and in adults, Bacillus and Bacillus cereus Group were registered in both localities. Gut bacterial richness was higher in adults from the Pacific with respect to the Atlantic Coast, while larval richness was similar in samples of both coasts. The Shannon index indicated uniformity in morphospecies abundances in both localities. Finally, the characterization of morphospecies from the gut of Anopheles albimanus mosquitoes from Colombia by culture-dependent methods complemented with 16S rRNA gene sequencing allowed the definition, at a finer resolution, of the composition and structure of these microbial communities. In addition, the obtained bacterial culture collection will allow further evaluation of the microorganisms for their potential as biocontrol agents.

Microanatomy of the American Malaria Vector Anopheles aquasalis (Diptera: Culicidae: Anophelinae) Midgut: Ultrastructural and Histochemical Observations

The mosquito gut is divided into foregut, midgut, and hindgut. The midgut functions in storage and digestion of the bloodmeal. This study used light, scanning (SEM), and transmission (TEM) electron microscopy to analyze in detail the microanatomy and morphology of the midgut of nonblood-fed Anopheles aquasalis females. The midgut epithelium is a monolayer of columnar epithelial cells that is composed of two populations: microvillar epithelial cells and basal cells. The microvillar epithelial cells can be further subdivided into light and dark cells, based on their affinities to toluidine blue and their electron density. FITC-labeling of the anterior midgut and posterior midgut with lectins resulted in different fluorescence intensities, indicating differences in carbohydrate residues. SEM revealed a complex muscle network composed of circular and longitudinal fibers that surround the entire midgut. In summary, the use of a diverse set of morphological methods revealed the general microanatomy of the midgut and associated tissues of An. aquasalis, which is a major vector of Plasmodium spp. (Haemosporida: Plasmodiidae) in America.

Anopheles aquasalis transcriptome reveals autophagic responses to Plasmodium vivax midgut invasion

Background

Elimination of malaria depends on mastering transmission and understanding the biological basis of Plasmodium infection in the vector. The first mosquito organ to interact with the parasite is the midgut and its transcriptomic characterization during infection can reveal effective antiplasmodial responses able to limit the survival of the parasite. The vector response to Plasmodium vivax is not fully characterized, and its specificities when compared with other malaria parasites can be of fundamental interest for specific control measures.

Methods

Experimental infections were performed using a membrane-feeding device. Three groups were used: P. vivax-blood-fed, blood-fed on inactivated gametocytes, and unfed mosquitoes. Twenty-four hours after feeding, the mosquitoes were dissected and the midgut collected for transcriptomic analysis using RNAseq. Nine cDNA libraries were generated and sequenced on an Illumina HiSeq2500. Readings were checked for quality control and analysed using the Trinity platform for de novo transcriptome assembly. Transcript quantification was performed and the transcriptome was functionally annotated. Differential expression gene analysis was carried out. The role of the identified mechanisms was further explored using functional approaches.

Results

Forty-nine genes were identified as being differentially expressed with P. vivax infection: 34 were upregulated and 15 were downregulated. Half of the P. vivax-related differentially expressed genes could be related to autophagy; therefore, the effect of the known inhibitor (wortmannin) and activator (spermidine) was tested on the infection outcome. Autophagic activation significantly reduced the intensity and prevalence of infection. This was associated with transcription alterations of the autophagy regulating genes Beclin, DRAM and Apg8.

Conclusions

Our data indicate that P. vivax invasion of An. aquasalis midgut epithelium triggers an autophagic response and its activation reduces infection. This suggests a novel mechanism that mosquitoes can use to fight Plasmodium infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3506-8) contains supplementary material, which is available to authorized users.

Inhibition of JNK signaling in the Asian malaria vector Anopheles stephensi extends mosquito longevity and improves resistance to Plasmodium falciparum infection

Malaria is a global health concern caused by infection with Plasmodium parasites. With rising insecticide and drug resistance, there is a critical need to develop novel control strategies, including strategies to block parasite sporogony in key mosquito vector species. MAPK signaling pathways regulated by extracellular signal-regulated kinases (ERKs) and the stress-activated protein kinases (SAPKs) c-Jun N-terminal kinases (JNKs) and p38 MAPKs are highly conserved across eukaryotes, including mosquito vectors of the human malaria parasite Plasmodium falciparum. Some of these pathways in mosquitoes have been investigated in detail, but the mechanisms of integration of parasite development and mosquito fitness by JNK signaling have not been elucidated. To this end, we engineered midgut-specific overexpression of MAPK phosphatase 4 (MKP4), which targets the SAPKs, and used two potent and specific JNK small molecule inhibitors (SMIs) to assess the effects of JNK signaling manipulations on Anopheles stephensi fecundity, lifespan, intermediary metabolism, and P. falciparum development. MKP4 overexpression and SMI treatment reduced the proportion of P. falciparum-infected mosquitoes and decreased oocyst loads relative to controls. SMI-treated mosquitoes exhibited no difference in lifespan compared to controls, whereas genetically manipulated mosquitoes exhibited extended longevity. Metabolomics analyses of SMI-treated mosquitoes revealed insights into putative resistance mechanisms and the physiology behind lifespan extension, suggesting for the first time that P. falciparum-induced JNK signaling reduces mosquito longevity and increases susceptibility to infection, in contrast to previously published reports, likely via a critical interplay between the invertebrate host and parasite for nutrients that play essential roles during sporogonic development.

Malaria is a global health concern caused by infection with Plasmodium parasites. With rising insecticide and drug resistance, there is a critical need to develop novel control strategies. One strategy is to develop a Plasmodium-resistant mosquito through the manipulation of key signaling pathways and processes in the mosquito midgut, a critical tissue for parasite development. MAPK signaling pathways are highly conserved among eukaryotes and regulate development of the human malaria parasite Plasmodium falciparum in the mosquito vector. Here, we investigated how manipulation of Anopheles stephensi JNK signaling affects development of P. falciparum and key mosquito life history traits. We used multiple, complementary approaches to demonstrate that malaria parasite infection activates mosquito JNK signaling for its own benefit at a cost to host lifespan. Notably, these combined effects derive from networked signaling with other transduction pathways and alterations to intermediary metabolism in the mosquito host.

An Anopheles aquasalis GATA factor Serpent is required for immunity against Plasmodium and bacteria

Innate immunity is an ancient and conserved defense system that provides an early effective response against invaders. Many immune genes of Anopheles mosquitoes have been implicated in defense against a variety of pathogens, including plasmodia. Nevertheless, only recent work identified some immune genes of Anopheles aquasalis mosquitoes upon P. vivax infection. Among these was a GATA transcription factor gene, which is described here. This is an ortholog of GATA factor Serpent genes described in Drosophila melanogaster and Anopheles gambiae. Gene expression analyses showed an increase of GATA-Serpent mRNA in P. vivax-infected A. aquasalis and functional RNAi experiments identified this transcription factor as an important immune gene of A. aquasalis against both bacteria and P. vivax. Besides, we were able to identify an effect of GATA-Serpent knockdown on A. aquasalis hemocyte proliferation and differentiation. These findings expand our understanding of the poorly studied A. aquasalis-P. vivax interactions and uncover GATA-Serpent as a key player of the mosquito innate immune response.

Gene expression profiles of the Southern house mosquito Culex quinquefasciatus during exposure to permethrin

Insecticide resistance is a major obstacle to the management of disease-vectoring mosquitoes worldwide. The genetic changes and detoxification genes involved in insecticide resistance have been extensively studied in populations of insecticide-resistant mosquitoes, however few studies have focused on the resistance genes upregulated upon insecticide exposure and the possible regulation pathways involved in insecticide resistance. To characterize the changes in gene expression during insecticide exposure, and to investigate the possible connection of known regulation pathways with insecticide resistance, we conducted RNA-Seq analysis of a highly permethrin-resistant strain of Culex quinquefasciatus following permethrin exposure. Gene expression profiles revealed a total of 224 upregulated and 146 downregulated genes when compared to a blank acetone carrier treated control, respectively, suggesting that there were multiple, but specific genes involved in permethrin resistance. Functional enrichment analysis showed that the upregulated genes contained multiple detoxification genes including a glutathione S-transferase and multiple cytochrome P450 genes, as well as several immune-related genes, while the downregulated genes consisted primarily of proteases and carbohydrate metabolism and transport. Further analysis showed that permethrin exposure resulted in a decrease in the expression of serum storage proteins and likely represented a delay in the development of the fourth instar possibly due to a decrease in feeding. This effect was more pronounced in an insecticide-resistant strain than in an insecticide-susceptible strain and may represent a behavioral mechanism of insecticide resistance in Culex mosquitoes.

Diverse Host and Restriction Factors Regulate Mosquito-Pathogen Interactions

Mosquitoes transmit diseases that seriously impact global human health. Despite extensive knowledge of the life cycles of mosquito-borne parasites and viruses within their hosts, control strategies have proven insufficient to halt their spread. An understanding of the relationships established between such pathogens and the host tissues they inhabit is therefore paramount for the development of new strategies that specifically target these interactions, to prevent the pathogens' maturation and transmission. Here we present an updated account of the antagonists and host factors that affect the development of Plasmodium, the parasite causing malaria, and mosquito-borne viruses, such as dengue virus and Zika virus, within their mosquito vectors, and we discuss the similarities and differences between Plasmodium and viral systems, looking toward the elucidation of new targets for disease control.

The role of the peritrophic matrix and red blood cell concentration in Plasmodium vivax infection of Anopheles aquasalis

Background

Plasmodium vivax is predominant in the Amazon region, and enhanced knowledge of its development inside a natural vector, Anopheles aquasalis, is critical for future strategies aimed at blocking parasite development. The peritrophic matrix (PM), a chitinous layer produced by the mosquito midgut in response to blood ingestion, is a protective barrier against pathogens. Plasmodium can only complete its life-cycle, and consequently be transmitted to a new host, after successfully passing this barrier. Interestingly, fully engorged mosquitoes that had a complete blood meal form a thicker, well-developed PM than ones that feed in small amounts. The amount of red blood cells (RBC) in the blood meal directly influences the production of digestive enzymes and can protect parasites from being killed during the meal digestion. A specific study interrupting the development of the PM associated with the proteolytic activity inhibition, and distinct RBC concentrations, during the P. vivax infection of the New World malaria vector An. aquasalis is expected to clarify whether these factors affect the parasite development.

Results

Absence of PM in the vector caused a significant reduction in P. vivax infection. However, the association of chitinase with trypsin inhibitor restored infection rates to those of mosquitoes with a structured PM. Also, only the ingestion of trypsin inhibitor by non-chitinase treated mosquitoes increased the infection intensity. Moreover, the RBC concentration in the infected P. vivax blood meal directly influenced the infection rate and its intensity. A straight correlation was observed between RBC concentrations and infection intensity.

Conclusions

This study established that there is a balance between the PM role, RBC concentration and digestive enzyme activity influencing the establishment and development of P. vivax infection inside An. aquasalis. Our results indicate that the absence of PM in the midgut facilitates digestive enzyme dispersion throughout the blood meal, causing direct damage to P. vivax. On the other hand, high RBC concentrations support a better and thick, well-developed PM and protect P. vivax from being killed. Further studies of this complex system may provide insights into other details of the malaria vector response to P. vivax infection.

Inhibition of the complement system by saliva of Anopheles (Nyssorhynchus) aquasalis

Anopheline mosquitoes are vectors of malaria parasites. Their saliva contains anti-hemostatic and immune-modulator molecules that favor blood feeding and parasite transmission. In this study, we describe the inhibition of the alternative pathway of the complement system (AP) by Anopheles aquasalis salivary gland extracts (SGE). According to our results, the inhibitor present in SGE acts on the initial step of the AP blocking deposition of C3b on the activation surfaces. Properdin, which is a positive regulatory molecule of the AP, binds to SGE. When SGE was treated with an excess of properdin, it was unable to inhibit the AP. Through SDS-PAGE analysis, A. aquasalis presented a salivary protein with the same molecular weight as recombinant complement inhibitors belonging to the SG7 family described in the saliva of other anopheline species. At least some SG7 proteins bind to properdin and are AP inhibitors. Searching for SG7 proteins in the A. aquasalis genome, we retrieved a salivary protein that shared an 85% identity with albicin, which is the salivary alternative pathway inhibitor from A. albimanus. This A. aquasalis sequence was also very similar (81% ID) to the SG7 protein from A. darlingi, which is also an AP inhibitor. Our results suggest that the salivary complement inhibitor from A. aquasalis is an SG7 protein that can inhibit the AP by binding to properdin and abrogating its stabilizing activity. Albicin, which is the SG7 from A. albimanus, can directly inhibit AP convertase. Given the high similarity of SG7 proteins, the SG7 from A. aquasalis may also directly inhibit AP convertase in the absence of properdin.

The transcription factor Relish controls Anaplasma marginale infection in the bovine tick Rhipicephalus microplus

Rhipicephalus microplus is an important biological vector of Anaplasma marginale, the etiological agent of bovine anaplasmosis. The knowledge of tick immune responses to control bacterial infections remains limited. In this study, we demonstrate that transcription factor Relish from the IMD signaling pathway has an important role in the control of A. marginale infection in ticks. We found that RNA-mediated silencing of Relish caused a significant increase in the number of A. marginale in the midgut and salivary glands of R. microplus. In addition, the IMD pathway regulates the expression of the gene that encodes the antimicrobial peptide (AMP) microplusin. Moreover, microplusin expression was up-regulated in the midgut (2×) and salivary glands (8×) of A. marginale infected R. microplus. Therefore, it is plausible to hypothesize that microplusin may be involved in the A. marginale control. This study provides the first evidence of IMD signaling pathway participation on the A. marginale control in R. microplus.

Quantitative real-time PCR analysis of Anopheles dirus TEP1 and NOS during Plasmodium berghei infection, using three reference genes

Quantitative reverse transcription PCR (qRT-PCR) has been an integral part of characterizing the immunity of Anopheles mosquitoes towards Plasmodium invasion. Two anti-Plasmodium factors of Anopheles, thioester-containing protein 1 (TEP1) and nitric oxide synthase (NOS), play a role in the refractoriness of Anopheles towards Plasmodium infection and are generally expressed during infection. However, these are less studied in Anopheles dirus, a dominant malaria vector in Southeast Asia. Furthermore, most studies used a single reference gene for normalization during gene expression analysis without proper validation. This may lead to erroneous quantification of expression levels. Therefore, the present study characterized and investigated the expression profiles of TEP1 and NOS of Anopheles dirus during P. berghei infection. Prior to that, the elongation factor 1-alpha (EF1), actin 1 (Act) and ribosomal protein S7 (S7) genes were validated for their suitability as a set of reference genes. TEP1 and NOS expressions in An. dirus were found to be significantly induced after P. berghei infection.

Apolipophorin-III Acts as a Positive Regulator of Plasmodium Development in Anopheles stephensi

Apolipophorin III (ApoLp-III) is a well-known hemolymph protein having a functional role in lipid transport and immune responses of insects. Here we report the molecular and functional characterization of Anopheles stephensi Apolipophorin-III (AsApoLp-III) gene. This gene consists of 679 nucleotides arranged into two exons of 45 and 540 bp that give an ORF encoding 194 amino acid residues. Excluding a putative signal peptide of the first 19 amino acid residues, the 175-residues in mature AsApoLp-III protein has a calculated molecular mass of 22 kDa. Phylogenetic analysis revealed the divergence of mosquitoes (Order Diptera) ApoLp-III from their counterparts in moths (Order: Lepidoptera). Also, it revealed a close relatedness of AsApoLp-III to ApoLp-III of An. gambiae. AsApoLp-III mRNA expression is strongly induced in Plasmodium berghei infected mosquito midguts suggesting its crucial role in parasite development. AsApoLp-III silencing decreased P. berghei oocysts numbers by 7.7 fold against controls. These effects might be due to the interruption of AsApoLp-III mediated lipid delivery to the developing oocysts. In addition, nitric oxide synthase (NOS), an antiplasmodial gene, is also highly induced in AsApoLp-III silenced midguts suggesting that this gene acts like an agonist and protects Plasmodium against the mosquito immunity.

Anopheles stephensi Heme Peroxidase HPX15 Suppresses Midgut Immunity to Support Plasmodium Development

The heme peroxidase HPX15 is an evolutionary conserved anopheline lineage-specific gene. Previously, we found that this gene is present in the genome of 19 worldwide distributed different species of Anopheles mosquito and its orthologs are absent in other mosquitoes, insects, or human. In addition, 65–99% amino acid identity among these 19 orthologs permitted us to hypothesize that the functional aspects of this gene might be also conserved in different anophelines. In this study, we found that Anopheles stephensi AsHPX15 gene is mainly expressed in the midgut and highly induced after uninfected or Plasmodium berghei-infected blood feeding. RNA interference-mediated silencing of midgut AsHPX15 gene drastically reduced the number of developing P. berghei oocysts. An antiplasmodial gene nitric oxide synthase was induced 13-fold in silenced midguts when compared to the unsilenced controls. Interestingly, the induction of antiplasmodial immunity in AsHPX15-silenced midguts is in absolute agreement with Anopheles gambiae. In A. gambiae, AgHPX15 catalyzes the formation of a dityrosine network at luminal side of the midgut that suppresses the activation of mosquito immunity against the bolus bacteria. Thus, a low-immunity zone created by this mechanism indirectly supports Plasmodium development inside the midgut lumen. These indistinguishable functional behaviors and conserved homology indicates that HPX15 might be a potent target to manipulate the antiplasmodial immunity of the anopheline midgut, and it will open new frontiers in the field of malaria control.

Proteases of haematophagous arthropod vectors are involved in blood-feeding, yolk formation and immunity - a review

Ticks, triatomines, mosquitoes and sand flies comprise a large number of haematophagous arthropods considered vectors of human infectious diseases. While consuming blood to obtain the nutrients necessary to carry on life functions, these insects can transmit pathogenic microorganisms to the vertebrate host. Among the molecules related to the blood-feeding habit, proteases play an essential role. In this review, we provide a panorama of proteases from arthropod vectors involved in haematophagy, in digestion, in egg development and in immunity. As these molecules act in central biological processes, proteases from haematophagous vectors of infectious diseases may influence vector competence to transmit pathogens to their prey, and thus could be valuable targets for vectorial control.

The transcriptome of the mosquito Aedes fluviatilis (Diptera: Culicidae), and transcriptional changes associated with its native Wolbachia infection

Background

Wolbachia is a bacterial endosymbiont that naturally infects a wide range of insect species, and causes drastic changes to host biology. Stable infections of Wolbachia in mosquitoes can inhibit infection with medically important pathogens such as dengue virus and malaria-causing Plasmodium parasites. However, some native Wolbachia strains can enhance infection with certain pathogens, as is the case for the mosquito Aedes fluviatilis, where infection with Plasmodium gallinaceum is enhanced by the native wFlu Wolbachia strain. To better understand the biological interactions between mosquitoes and native Wolbachia infections, and to investigate the process of pathogen enhancement, we used RNA-Seq to generate the transcriptome of Ae. fluviatilis with and without Wolbachia infection.

Results

In total, we generated 22,280,160 Illumina paired-end reads from Wolbachia-infected and uninfected mosquitoes, and used these to make a de novo transcriptome assembly, resulting in 58,013 contigs with a median sequence length of 443 bp and an N50 of 2454 bp. Contigs were annotated through local alignments using BlastX, and associated with both gene ontology and KEGG orthology terms. Through baySeq, we identified 159 contigs that were significantly upregulated due to Wolbachia infection, and 98 that were downregulated. Critically, we saw no changes to Toll or IMD immune gene transcription, but did see evidence that wFlu infection altered the expression of several bacterial recognition genes, and immune-related genes that could influence Plasmodium infection. wFlu infection also had a widespread effect on a number of host physiological processes including protein, carbohydrate and lipid metabolism, and oxidative stress. We then compared our data set with transcriptomic data for other Wolbachia infections in Aedes aegypti, and identified a core set of 15 gene groups associated with Wolbachia infection in mosquitoes.

Conclusions

While the scale of transcriptional changes associated with wFlu infection might be small, the scope is rather large, which confirms that native Wolbachia infections maintain intricate molecular relationships with their mosquito hosts even after lengthy periods of co-evolution. We have also identified several potential means through which wFlu infection might influence Plasmodium infection in Ae. fluviatilis, and these genes should form the basis of future investigation into the enhancement of Plasmodium by Wolbachia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3441-4) contains supplementary material, which is available to authorized users.

Plasmodium yoelii nigeriensis (N67) Is a Robust Animal Model to Study Malaria Transmission by South American Anopheline Mosquitoes

Malaria is endemic in the American continent and the Amazonian rainforest is the region with the highest risk of transmission. However, the lack of suitable experimental models to infect malaria vectors from the Americas has limited the progress to understand the biology of transmission in this region. Anopheles aquasalis, a major vector in coastal areas of South America, was found to be highly refractory to infection with two strains of Plasmodium falciparum (NF54 and 7G8) and with Plasmodium berghei (mouse malaria), even when the microbiota was eliminated with antibiotics and oxidative stress was reduced with uric acid. In contrast, An. aquasalis females treated with antibiotics and uric acid are susceptible to infection with a second murine parasite, Plasmodium yoelii nigeriensis N67 (PyN67). Anopheles albimanus, one of the main malaria vectors in Central America, Southern Mexico and the Caribbean, was more susceptible to infection with PyN67 than An. aquasalis, even in the absence of any pre-treatment, but was still less susceptible than Anopheles stephensi. Disruption of the complement-like system in An. albimanus significantly enhanced PyN67 infection, indicating that the mosquito immune system is mounting effective antiplasmodial responses. PyN67 has the ability to infect a broad range of anophelines and is an excellent model to study malaria transmission by South American vectors.

Diet-Induced Nutritional Stress and Pathogen Interference in Wolbachia-Infected Aedes aegypti

The pathogen interference phenotype greatly restricts infection with dengue virus (DENV) and other pathogens in Wolbachia-infected Aedes aegypti, and is a vital component of Wolbachia-based mosquito control. Critically, the phenotype's causal mechanism is complex and poorly understood, with recent evidence suggesting that the cause may be species specific. To better understand this important phenotype, we investigated the role of diet-induced nutritional stress on interference against DENV and the avian malarial parasite Plasmodium gallinaceum in Wolbachia-infected Ae. aegypti, and on physiological processes linked to the phenotype. Wolbachia-infected mosquitoes were fed one of four different concentrations of sucrose, and then challenged with either P. gallinaceum or DENV. Interference against P. gallinaceum was significantly weakened by the change in diet however there was no effect on DENV interference. Immune gene expression and H2O2 levels have previously been linked to pathogen interference. These traits were assayed for mosquitoes on each diet using RT-qPCR and the Amplex Red Hydrogen Peroxide/Peroxidase Assay Kit, and it was observed that the change in diet did not significantly affect immune expression, but low carbohydrate levels led to a loss of ROS induction in Wolbachia-infected mosquitoes. Our data suggest that host nutrition may not influence DENV interference for Wolbachia-infected mosquitoes, but Plasmodium interference may be linked to both nutrition and oxidative stress. This pathogen-specific response to nutritional change highlights the complex nature of interactions between Wolbachia and pathogens in mosquitoes.

Mosquito gut antiparasitic and antiviral immunity

Mosquitoes are responsible for the transmission of diseases with a serious impact on global human health, such as malaria and dengue. All mosquito-transmitted pathogens complete part of their life cycle in the insect gut, where they are exposed to mosquito-encoded barriers and active factors that can limit their development. Here we present the current understanding of mosquito gut immunity against malaria parasites, filarial worms, and viruses such as dengue, Chikungunya, and West Nile. The most recently proposed immune mediators involved in intestinal defenses are discussed, as well as the synergies identified between the recognition of gut microbiota and the mounting of the immune response.

The evolutionary divergence of STAT transcription factor in different Anopheles species

Anopheles mosquito transmits Plasmodium, the malaria causing parasite. Different species of Anopheles mosquito dominate in a particular geographical location and are capable of transmitting specific strains of Plasmodium. It is important to understand the biology of different anophelines to control the parasite transmission. STAT is an evolutionary conserved transcription factor that regulates the parasite development in African malaria vector Anopheles gambiae. Unlike Drosophila and Aedes aegypti, where a single STAT gene plays an important role in immunity, An. gambiae contains one evolutionary conserved STAT-A and another retro-duplicated, introns-less STAT-B gene. To find out whether other species of Anopheles also have two STATs, the available genomic data of different anophelines were used to annotate their STATs through in silico analyses. Our results revealed that Indian malaria vector An. stephensi genome contains two STATs, AsSTAT-A and AsSTAT-B genes. These genes were cloned and confirmed by sequencing. Both AsSTATs were found to be expressed in different development stages of mosquito. However, the relative mRNA levels of evolutionary conserved AsSTAT-A gene were always higher than the retroduplicated AsSTAT-B gene. STAT pathway was activated upon Plasmodium berghei infection, indicated its role in immunity. Furthermore, comparative in silico analysis of eighteen Anopheles species revealed that five species: An. sinensis, An. albimanus, An. darlingi, An. dirus andAn. farauti do not contain STAT-B gene in their genome. Interestingly, thirteen species of the subgenus Anopheles and Cellia that contain both STATs were also mutually diverged. This consequence leads to sequence variability in some significant protein motifs within the STAT-B genes. Phylogenetic analyses indicated that an independent, lineage-specific duplication occurred in the subgenus Cellia after the diversification of series Neomyzomyia from its last common ancestor. In An. atroparvus (subgenus Anopheles), STAT gene underwent recent lineage-specific duplication and give rise to a highly similar STAT-B gene. This suggested that the genetic divergence in various Anopheles species might appeared due to their adaptations to the altered environmental conditions or pathogen encounters.

Role of NF-kβ factor Rel2 during Plasmodium falciparum and bacterial infection in Anopheles dirus

BACKGROUND

Anopheles mosquitoes transmit malaria which is one of the world's most threatening diseases. Anopheles dirus (sensu stricto) is among the main vectors of malaria in South East Asia. The mosquito innate immune response is the first line of defence against malaria parasites during its development. The immune deficiency (IMD) pathway, a conserved immune signaling pathway, influences anti-Plasmodium falciparum activity in Anopheles gambiae, An. stephensi and An. albimanus. The aim of the study was to determine the role of Rel2, an IMD pathway-controlled NF-kappaβ transcription factor, in An. dirus.

METHODS

RACE (Rapid amplification of cDNA ends) was performed on the Rel2 gene. Double-stranded Rel2 was constructed and injected into the thorax of female mosquitoes. The injected mosquitoes were fed on a P. falciparum gametocyte culture and dissected on day 7-9 post-feeding in order to count the oocysts. A survival analysis was conducted by exposing the dsRNA injected mosquitoes to Gram-positive and Gram-negative bacteria.

RESULTS

This study demonstrated that the Rel2 gene in An. dirus has two isoforms, short length and full length. RNA interference-mediated gene silencing of Rel2 showed that the latter is involved in protection against P. falciparum, Gram-positive bacteria (Micrococcus luteus) with Lys-type peptidoglycan and Gram-negative bacteria (Escherichia coli) with DAP-type peptidoglycan.

CONCLUSION

This study suggested that there are similarities in the splicing events and functionality of the Rel2 gene, between the Anopheles species. Among all the important anophelines, the immunity of only a few has been thoroughly investigated. In order to develop novel vector-based control strategies and restrict malaria transmission, the immune pathways of these important vectors should be thoroughly investigated.

Silencing of Anopheles stephensi Heme Peroxidase HPX15 Activates Diverse Immune Pathways to Regulate the Growth of Midgut Bacteria

Anopheles mosquito midgut harbors a diverse group of endogenous bacteria that grow extensively after the blood feeding and help in food digestion and nutrition in many ways. Although, the growth of endogenous bacteria is regulated by various factors, however, the robust antibacterial immune reactions are generally suppressed in this body compartment by a heme peroxidase HPX15 crosslinked mucins barrier. This barrier is formed on the luminal side of the midgut and blocks the direct interactions and recognition of bacteria or their elicitors by the immune reactive midgut epithelium. We hypothesized that in the absence of HPX15, an increased load of exogenous bacteria will enormously induce the mosquito midgut immunity and this situation in turn, can easily regulate mosquito-pathogen interactions. In this study, we found that the blood feeding induced AsHPX15 gene in Anopheles stephensi midgut and promoted the growth of endogenous as well as exogenous fed bacteria. In addition, the mosquito midgut also efficiently regulated the number of these bacteria through the induction of classical Toll and Imd immune pathways. In case of AsHPX15 silenced midguts, the growth of midgut bacteria was largely reduced through the induction of nitric oxide synthase (NOS) gene, a downstream effector molecule of the JAK/STAT pathway. Interestingly, no significant induction of the classical immune pathways was observed in these midguts. Importantly, the NOS is a well known negative regulator of Plasmodium development, thus, we proposed that the induction of diverged immune pathways in the absence of HPX15 mediated midgut barrier might be one of the strategies to manipulate the vectorial capacity of Anopheles mosquito.

Infection of laboratory colonies of Anopheles mosquitoes with Plasmodium vivax from cryopreserved clinical isolates

Plasmodium vivax is the most geographically widespread malaria parasite. Unique features of transmission biology complicate P. vivax control. Interventions targeting transmission are required for malaria eradication. In the absence of an in vitro culture, transmission studies rely on live isolates from non-human primates or endemic regions. Here, we demonstrate P. vivax gametocytes from both India and Brazil are stable during cryopreservation. Importantly, cryopreserved gametocytes from Brazil were capable of infecting three anopheline mosquito species in feedings done in the United States. These findings create new opportunities for transmission studies in diverse locales.

Exploring the immune signalling pathway-related genes of the cattle tick Rhipicephalus microplus: From molecular characterization to transcriptional profile upon microbial challenge

In dipteran insects, invading pathogens are selectively recognized by four major pathways, namely Toll, IMD, JNK, and JAK/STAT, and trigger the activation of several immune effectors. Although substantial advances have been made in understanding the immunity of model insects such as Drosophila melanogaster, knowledge on the activation of immune responses in other arthropods such as ticks remains limited. Herein, we have deepened our understanding of the intracellular signalling pathways likely to be involved in tick immunity by combining a large-scale in silico approach with high-throughput gene expression analysis. Data from in silico analysis revealed that although both the Toll and JAK/STAT signalling pathways are evolutionarily conserved across arthropods, ticks lack central components of the D. melanogaster IMD pathway. Moreover, we show that tick immune signalling-associated genes are constitutively transcribed in BME26 cells (a cell lineage derived from embryos of the cattle tick Rhipicephalus microplus) and exhibit different transcriptional patterns in response to microbial challenge. Interestingly, Anaplasma marginale, a pathogen that is naturally transmitted by R. microplus, causes downregulation of immune-related genes, suggesting that this pathogen may manipulate the tick immune system, favouring its survival and vector colonization.

Remote Control of Intestinal Stem Cell Activity by Haemocytes in Drosophila

The JAK/STAT pathway is a key signaling pathway in the regulation of development and immunity in metazoans. In contrast to the multiple combinatorial JAK/STAT pathways in mammals, only one canonical JAK/STAT pathway exists in Drosophila. It is activated by three secreted proteins of the Unpaired family (Upd): Upd1, Upd2 and Upd3. Although many studies have established a link between JAK/STAT activation and tissue damage, the mode of activation and the precise function of this pathway in the Drosophila systemic immune response remain unclear. In this study, we used mutations in upd2 and upd3 to investigate the role of the JAK/STAT pathway in the systemic immune response. Our study shows that haemocytes express the three upd genes and that injury markedly induces the expression of upd3 by the JNK pathway in haemocytes, which in turn activates the JAK/STAT pathway in the fat body and the gut. Surprisingly, release of Upd3 from haemocytes upon injury can remotely stimulate stem cell proliferation and the expression of Drosomycin-like genes in the intestine. Our results also suggest that a certain level of intestinal epithelium renewal is required for optimal survival to septic injury. While haemocyte-derived Upd promotes intestinal stem cell activation and survival upon septic injury, haemocytes are dispensable for epithelium renewal upon oral bacterial infection. Our study also indicates that intestinal epithelium renewal is sensitive to insults from both the lumen and the haemocoel. It also reveals that release of Upds by haemocytes coordinates the wound-healing program in multiple tissues, including the gut, an organ whose integrity is critical to fly survival.

Molecular characterization of SOCS gene and its expression analysis on Plasmodium berghei infection in Anopheles culicifacies

Anopheles culicifacies mosquitoes are able to transmit both falciparum and vivax malaria in India. More than 65% of malaria cases reported annually spread through this vector. Despite the fact that it poses major vectorial burden in India, the molecular basis of its immune role against Plasmodium development has not been explored intensively. Here, we characterized An. culicifacies SOCS (suppressor of cytokine signaling) gene, a regulator of STAT pathway and its expression analysis upon Plasmodium infection. Our analysis has demonstrated that An. culicifacies SOCS gene shares strikingly high level of sequence similarity in SH2 domain and SOCS box region with other mosquito species. However, its N-terminal identity is limited to Anophelines mosquito only, suggesting its genus specific role. SOCS mRNA is expressed in all developmental stages of mosquito and its expression is higher in male than female adults. SOCS mRNA is significantly induced after Plasmodium infection in midgut tissue indicating its involvement in the immune defense responses. This is the first evidence of involvement of SOCS as an immune gene in Indian malaria vector An. culicifacies.

Plasmodium berghei induced priming in Anopheles albimanus independently of bacterial co-infection

Priming in invertebrates is the acquired capacity to better combat a pathogen due to a previous exposure to sub-lethal doses of the same organism. It is proposed to be functionally analogous to immune memory in vertebrates. Previous studies with Anopheles gambiae mosquitoes provide evidence that the inhibitory response to a second challenge by the malaria parasite Plasmodium berghei resulted from a sustained activation of hemocytes by midgut bacteria. These bacteria probably accessed the hemolymph during a first aborted infection through lesions produced by parasites invading the midgut. Since the mosquito immune responses to midgut bacteria and Plasmodium overlap, it is difficult to determine the priming responses of each. We herein document priming induced in the aseptic An. albimanus midgut by P. berghei, probably independent of the immune response induced by midgut bacteria. This idea is further evidenced by experiments with Pbs 25-28 knock out parasites (having an impaired capacity for invading the mosquito midgut) and dead ookinetes. Priming protection against a homologous challenge with P. berghei lasted up to 12 days. There was greater incorporation of 5-bromo-2'-deoxyuridine into midgut cell nuclei (indicative of DNA synthesis without mitosis) and increased transcription of hnt (a gene required for the endocycle of midgut cells) in primed versus unprimed mosquitoes, suggesting that endoreplication was the underlying mechanism of priming. Moreover, the transcription of hnt and antimicrobial peptides related to an anti-Plasmodium response (attacin, cecropin and gambicin) was enhanced in a biphasic rather than sustained response after priming An. albimanus with P. berghei.

The Plasmodium bottleneck: malaria parasite losses in the mosquito vector

Nearly one million people are killed every year by the malaria parasite Plasmodium. Although the disease-causing forms of the parasite exist only in the human blood, mosquitoes of the genus Anopheles are the obligate vector for transmission. Here, we review the parasite life cycle in the vector and highlight the human and mosquito contributions that limit malaria parasite development in the mosquito host. We address parasite killing in its mosquito host and bottlenecks in parasite numbers that might guide intervention strategies to prevent transmission.

Hemocyte differentiation mediates the mosquito late-phase immune response against Plasmodium in Anopheles gambiae

Plasmodium parasites must complete development in the mosquito vector for transmission to occur. The mosquito innate immune response is remarkably efficient in limiting parasite numbers. Previous work has identified a LPS-induced TNFα transcription factor (LITAF)-like transcription factor, LITAF-like 3 (LL3), which significantly influences parasite numbers. Here, we demonstrate that LL3 does not influence invasion of the mosquito midgut epithelium or ookinete-to-oocyst differentiation but mediates a late-phase immune response that decreases oocyst survival. LL3 expression in the midgut and hemocytes is activated by ookinete midgut invasion and is independent of the mosquito microbiota, suggesting that LL3 may be a component of a wound-healing response. LL3 silencing abrogates the ability of mosquito hemocytes to differentiate and respond to parasite infection, implicating hemocytes as critical modulators of the late-phase immune response.

Transcriptome analysis of BmN cells following over-expression of BmSTAT

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway are involved in immune response, cell proliferation, differentiation, cell migration and apoptosis. In order to better understand the role of the JAK/STAT pathway in insects we chose Bombyx mori as an experimental model system. Over-expression of BmSTAT in a BmN cell line increased the number of cells in the G2 phase of the cell cycle. Genome-wide transcriptome analysis was performed to identify genes that were differentially expressed following BmSTAT overexpression. Transcriptome data showed that 10,853 and 10,129 expressed genes were obtained from the normal BmN cells and transformed cells, respectively. A total of 800 differentially expressed genes (DEGs) were detected, of which 787 were up-regulated and 13 were down-regulated with T test. In case of FC-test, 252 DEGs were detected, and 123 were expressed in the transformed cells and remaining were in the normal cells. Gene ontology (GO) annotation predicted a functional role for DEGs in catalytic activity, binding, transport, biological regulation, cellular and metabolic processes and pigmentation, while Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed the affected genes to be involved in a multitude of cell signaling pathways. Our findings implicate JAK/STAT signaling in regulating the cell cycle in Bombyx mori, probably in combination with other pathways. These findings justify further investigation into the functional role of the BmSTAT gene.

An overview of malaria transmission from the perspective of Amazon Anopheles vectors

In the Americas, areas with a high risk of malaria transmission are mainly located in the Amazon Forest, which extends across nine countries. One keystone step to understanding the Plasmodium life cycle in Anopheles species from the Amazon Region is to obtain experimentally infected mosquito vectors. Several attempts to colonise Anopheles species have been conducted, but with only short-lived success or no success at all. In this review, we review the literature on malaria transmission from the perspective of its Amazon vectors. Currently, it is possible to develop experimental Plasmodium vivax infection of the colonised and field-captured vectors in laboratories located close to Amazonian endemic areas. We are also reviewing studies related to the immune response to P. vivax infection of Anopheles aquasalis, a coastal mosquito species. Finally, we discuss the importance of the modulation of Plasmodium infection by the vector microbiota and also consider the anopheline genomes. The establishment of experimental mosquito infections with Plasmodium falciparum, Plasmodium yoelii and Plasmodium berghei parasites that could provide interesting models for studying malaria in the Amazonian scenario is important. Understanding the molecular mechanisms involved in the development of the parasites in New World vectors is crucial in order to better determine the interaction process and vectorial competence.