Exposure of Anopheles mosquitoes to trypanosomes reduces reproductive fitness and enhances susceptibility to Plasmodium

Aedes aegypti Beta-1,3-Glucan-Binding Protein Inhibits Dengue and ZIKA Virus Replication

GNBPB6, a beta-1,3-glucan-binding protein, was identified in the transcriptome of Aedes aegypti (A. aegypti) with dengue (DENV), Zika (ZIKV), and chikungunya viruses (CHIKV). In this study, we not only clarified that DENV2 and ZIKV regulate the changes in GNBPB6 expression but also identified the relationship of this gene with viral infections. The changes in GNBPB6 expression were quantified and showed a decrease in A. aegypti cells (Aag2 cells) at 2 dpi and 3 dpi and an increase at 4 dpi and 5 dpi (p < 0.05). A significant increase was observed only at 5 dpi after DENV2 infection. Subsequently, a GNBPB6 knockout (KO) cell line was constructed using the CRISPR/Cas9 system, and the DENV2 and ZIKV RNA copies, along with cell densities, were quantified and compared between the KO and wild type (WT) cells at different dpi. The result showed that DENV2 and ZIKV RNA copies were significantly increased in the KO cell line with no significant change in cell growth. Finally, DENV2 copies decreased after GNBPB6 was complemented in the KO. In conclusion, GNBPB6 knockout and complementation in Aag2 cells revealed that GNBPB6 can inhibit the replication of both DENV2 and ZIKV. These results contribute to subsequent research on mosquito-virus interactions.

The voltage-gated sodium channel, para, limits Anopheles coluzzii vector competence in a microbiota dependent manner

The voltage-gated sodium channel, para, is a target of DDT and pyrethroid class insecticides. Single nucleotide mutations in para, called knockdown resistant or kdr, which contribute to resistance against DDT and pyrethroid insecticides, have been correlated with increased susceptibility of Anopheles to the human malaria parasite Plasmodium falciparum. However, a direct role of para activity on Plasmodium infection has not yet been established. Here, using RNA-mediated silencing, we provide in vivo direct evidence for the requirement of wild-type (wt) para function for insecticide activity of deltamethrin. Depletion of wt para, which is susceptible to insecticide, causes deltamethrin tolerance, indicating that insecticide-resistant kdr alleles are likely phenocopies of loss of para function. We then show that normal para activity in An. coluzzii limits Plasmodium infection prevalence for both P. falciparum and P. berghei. A transcriptomic analysis revealed that para activity does not modulate the expression of immune genes. However, loss of para function led to enteric dysbiosis with a significant increase in the total bacterial abundance, and we show that para function limiting Plasmodium infection is microbiota dependent. In the context of the bidirectional "enteric microbiota-brain" axis studied in mammals, these results pave the way for studying whether the activity of the nervous system could control Anopheles vector competence.

Vector competence of Anopheles stephensi for O'nyong-nyong virus: a risk for global virus spread

BACKGROUND

O'nyong-nyong virus (ONNV) is a mosquito-borne alphavirus causing sporadic outbreaks of febrile illness with rash and polyarthralgia. Up to now, ONNV has been restricted to Africa and only two competent vectors have been found, Anopheles gambiae and An. funestus, which are also known malaria vectors. With globalization and invasive mosquito species migrating to ONNV endemic areas, there is a possible risk of introduction of the virus to other countries and continents. Anopheles stephensi, is closely related to An. gambiae and one of the invasive mosquito species of Asian origin that is now present in the Horn of Africa and spreading further east. We hypothesize that An. stephensi, a known primary urban malaria vector, may also serve as a new possible vector for ONNV.

METHODS

One-week-old female adult An. stephensi were exposed to ONNV-infected blood, and the vector competence for ONNV, i.e. infection rates (IRs), dissemination rates (DRs), transmission rates (TRs), dissemination efficiency (DEs) and transmission efficiency (TEs), were evaluated. Infection (IRs), dissemination efficiency (DEs) and transmission efficiency (TEs) were determined. Detection of ONNV RNA was analysed by RT-qPCR in the thorax and abdomen, head, wings, legs and saliva of the infected mosquitoes at four different time points, day 7, 14, 21 and 28 after blood meal. Infectious virus in saliva was assessed by infection of Vero B4 cells.

RESULTS

The mean mortality across all sampling times was 27.3% (95 confidence interval [CI] 14.7-44.2%). The mean rate of infection across all sampling periods was 89.5% (95% CI 70.6-95.9). The mean dissemination rate across sampling intervals was 43.4% (95% CI 24.3-64.2%). The mean TR and TE across all mosquito sampling time intervals were 65.3 (95% CI 28.6-93.5) and 74.6 (95% CI 52.1-89.4). The IR was 100%, 79.3%, 78.6% and 100% respectively at 7, 14, 21 and 28 dpi. The DR was the highest at 7 dpi with 76.0%, followed by 28 dpi at 57.1%, 21 dpi at 27.3% and 14 dpi at the lowest DR of 13.04%. DE was 76%, 13.8%, 25%, 57.1% and TR was 79%, 50%, 57.1% and 75% at 7, 14, 21 and 28 dpi respectively. The TE was the highest at 28 dpi, with a proportion of 85.7%. For 7, 14 and 21 dpi the transmission efficiency was 72.0%, 65.5% and 75.0% respectively.

CONCLUSION

Anopheles stephensi is a competent vector for ONNV and being an invasive species spreading to different parts of the world will likely spread the virus to other regions.

Determinants of Chikungunya and O'nyong-Nyong Virus Specificity for Infection of Aedes and Anopheles Mosquito Vectors

Mosquito-borne diseases caused by viruses and parasites are responsible for more than 700 million infections each year. Anopheles and Aedes are the two major vectors for, respectively, malaria and arboviruses. Anopheles mosquitoes are the primary vector of just one known arbovirus, the alphavirus o'nyong-nyong virus (ONNV), which is closely related to the chikungunya virus (CHIKV), vectored by Aedes mosquitoes. However, Anopheles harbor a complex natural virome of RNA viruses, and a number of pathogenic arboviruses have been isolated from Anopheles mosquitoes in nature. CHIKV and ONNV are in the same antigenic group, the Semliki Forest virus complex, are difficult to distinguish via immunodiagnostic assay, and symptomatically cause essentially the same human disease. The major difference between the arboviruses appears to be their differential use of mosquito vectors. The mechanisms governing this vector specificity are poorly understood. Here, we summarize intrinsic and extrinsic factors that could be associated with vector specificity by these viruses. We highlight the complexity and multifactorial aspect of vectorial specificity of the two alphaviruses, and evaluate the level of risk of vector shift by ONNV or CHIKV.

Meta-Analysis of Immune Induced Gene Expression Changes in Diverse Drosophila melanogaster Innate Immune Responses

Simple Summary

Organisms can be infected by a wide range of pathogens, including bacteria, viruses, and parasites. Following infection, the host mounts an immune response to attempt to eliminate the pathogen. These responses are often specific to the type of pathogen and mediated by the expression of specialized genes. We have characterized the expression changes induced in host Drosophila fruit flies following infection by multiple types of pathogens, and identified a small number of genes that show expression changes in each infection. This includes genes that are known to be involved in pathogen resistance, and others that have not been previously studied as immune response genes. These findings provide new insight into transcriptional changes that accompany Drosophila immunity. They may suggest possible roles for the differentially expressed genes in innate immune responses to diverse classes of pathogens, and serve to identify candidate genes for further empirical study of these processes.

Abstract

Organisms are commonly infected by a diverse array of pathogens and mount functionally distinct responses to each of these varied immune challenges. Host immune responses are characterized by the induction of gene expression, however, the extent to which expression changes are shared among responses to distinct pathogens is largely unknown. To examine this, we performed meta-analysis of gene expression data collected from Drosophila melanogaster following infection with a wide array of pathogens. We identified 62 genes that are significantly induced by infection. While many of these infection-induced genes encode known immune response factors, we also identified 21 genes that have not been previously associated with host immunity. Examination of the upstream flanking sequences of the infection-induced genes lead to the identification of two conserved enhancer sites. These sites correspond to conserved binding sites for GATA and nuclear factor κB (NFκB) family transcription factors and are associated with higher levels of transcript induction. We further identified 31 genes with predicted functions in metabolism and organismal development that are significantly downregulated following infection by diverse pathogens. Our study identifies conserved gene expression changes in Drosophila melanogaster following infection with varied pathogens, and transcription factor families that may regulate this immune induction.

Vector microbiota and immunity: modulating arthropod susceptibility to vertebrate pathogens

Arthropods, including mosquitoes, sand flies, tsetse flies, and ticks are vectors of many bacterial, parasitic, and viral pathogens that cause serious disease in humans and animals. Their microbiota, that is, all microorganisms that dwell within their tissues, can impact vector immunity and susceptibility to pathogen infection. Historically, host-pathogen-microbiota interactions have not been well described, with little known about mechanism. In this review, we highlight recent advances in understanding how individual microorganisms and microbial communities interact with vectors and human pathogens, the mechanisms they utilize to achieve these effects, and the potential for exploiting these interactions to control pathogen transmission. These studies fill important knowledge gaps and further our understanding of the roles that the vector microbiota plays in pathogen transmission.

Microbiomes of Blood-Feeding Arthropods: Genes Coding for Essential Nutrients and Relation to Vector Fitness and Pathogenic Infections. A Review

BACKGROUND

Blood-feeding arthropods support a diverse array of symbiotic microbes, some of which facilitate host growth and development whereas others are detrimental to vector-borne pathogens. We found a common core constituency among the microbiota of 16 different arthropod blood-sucking disease vectors, including Bacillaceae, Rickettsiaceae, Anaplasmataceae, Sphingomonadaceae, Enterobacteriaceae, Pseudomonadaceae, Moraxellaceae and Staphylococcaceae. By comparing 21 genomes of common bacterial symbionts in blood-feeding vectors versus non-blooding insects, we found that certain enteric bacteria benefit their hosts by upregulating numerous genes coding for essential nutrients. Bacteria of blood-sucking vectors expressed significantly more genes (p < 0.001) coding for these essential nutrients than those of non-blooding insects. Moreover, compared to endosymbionts, the genomes of enteric bacteria also contained significantly more genes (p < 0.001) that code for the synthesis of essential amino acids and proteins that detoxify reactive oxygen species. In contrast, microbes in non-blood-feeding insects expressed few gene families coding for these nutrient categories. We also discuss specific midgut bacteria essential for the normal development of pathogens (e.g., Leishmania) versus others that were detrimental (e.g., bacterial toxins in mosquitoes lethal to Plasmodium spp.).

Malaria-Resistant Mosquitoes (Diptera: Culicidae); The Principle is Proven, But Will the Effectors Be Effective?

Over the last few decades, a substantial number of anti-malarial effector genes have been evaluated for their ability to block parasite infection in the mosquito vector. While many of these approaches have yielded significant effects on either parasite intensity or prevalence of infection, just a few have been able to completely block transmission. Additionally, many approaches, while effective against the parasite, also disrupt or alter important aspects of mosquito physiology, leading to corresponding changes in lifespan, reproduction, and immunity. As the most promising approaches move towards field-based evaluation, questions of effector gene robustness and durability move to the forefront. In this forum piece, we critically evaluate past effector gene approaches with an eye towards developing a deeper pipeline to augment the current best candidates.

The Axenic and Gnotobiotic Mosquito: Emerging Models for Microbiome Host Interactions

The increasing availability of modern research tools has enabled a revolution in studies of non-model organisms. Yet, one aspect that remains difficult or impossible to control in many model and most non-model organisms is the presence and composition of the host-associated microbiota or the microbiome. In this review, we explore the development of axenic (microbe-free) mosquito models and what these systems reveal about the role of the microbiome in mosquito biology. Additionally, the axenic host is a blank template on which a microbiome of known composition can be introduced, also known as a gnotobiotic organism. Finally, we identify a "most wanted" list of common mosquito microbiome members that show the greatest potential to influence host phenotypes. We propose that these are high-value targets to be employed in future gnotobiotic studies. The use of axenic and gnotobiotic organisms will transition the microbiome into another experimental variable that can be manipulated and controlled. Through these efforts, the mosquito will be a true model for examining host microbiome interactions.

Possible influence of Plasmodium/Trypanosoma co-infections on the vectorial capacity of Anopheles mosquitoes

Objective

In tropical Africa, trypanosomiasis is present in endemic areas with many other diseases including malaria. Because malaria vectors become more anthropo-zoophilic under the current insecticide pressure, they may be exposed to trypanosome parasites. By collecting mosquitoes in six study sites with distinct malaria infection prevalence and blood sample from cattle, we tried to assess the influence of malaria-trypanosomiasis co-endemicity on the vectorial capacity of Anopheles.

Results

Overall, all animal infections were due to Trypanosoma vivax (infection rates from 2.6 to 10.5%) in villages where the lowest Plasmodium prevalence were observed at the beginning of the study. An. gambiae s.l. displayed trophic preferences for human-animal hosts. Over 84 mosquitoes, only one was infected by Plasmodium falciparum (infection rate: 4.5%) in a site that displayed the highest prevalence at the beginning of the study. Thus, Anopheles could be exposed to Trypanosoma when they feed on infected animals. No Plasmodium infection was observed in the Trypanosoma-infected animals sites. This can be due to an interaction between both parasites as observed in mice and highlights the need of further studies considering Trypanosoma/Plasmodium mixed infections to better characterize the role of these infections in the dynamic of malaria transmission and the mechanisms involved.