Global seroprevalence of Zika virus in asymptomatic individuals: A systematic review

BACKGROUND

Zika virus (ZIKV) has spread to five of the six World Health Organization (WHO) regions. Given the substantial number of asymptomatic infections and clinical presentations resembling those of other arboviruses, estimating the true burden of ZIKV infections is both challenging and essential. Therefore, we conducted a systematic review and meta-analysis of seroprevalence studies of ZIKV IgG in asymptomatic population to estimate its global impact and distribution.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted extensive searches and compiled a collection of articles published from Jan/01/2000, to Jul/31/2023, from Embase, Pubmed, SciELO, and Scopus databases. The random effects model was used to pool prevalences, reported with their 95% confidence interval (CI), a tool to assess the risk of study bias in prevalence studies, and the I2 method for heterogeneity (PROSPERO registration No. CRD42023442227). Eighty-four studies from 49 countries/territories, with a diversity of study designs and serological tests were included. The global seroprevalence of ZIKV was 21.0% (95%CI 16.1%-26.4%). Evidence of IgG antibodies was identified in all WHO regions, except for Europe. Seroprevalence correlated with the epidemics in the Americas (39.9%, 95%CI:30.0-49.9), and in some Western Pacific countries (15.6%, 95%CI:8.2-24.9), as well as with recent and past circulation in Southeast Asia (22.8%, 95%CI:16.5-29.7), particularly in Thailand. Additionally, sustained low circulation was observed in Africa (8.4%, 95%CI:4.8-12.9), except for Gabon (43.7%), and Burkina Faso (22.8%). Although no autochthonous transmission was identified in the Eastern Mediterranean, a seroprevalence of 16.0% was recorded.

CONCLUSIONS/SIGNIFICANCE

The study highlights the high heterogeneity and gaps in the distribution of seroprevalence. The implementation of standardized protocols and the development of tests with high specificity are essential for ensuring a valid comparison between studies. Equally crucial are vector surveillance and control methods to reduce the risk of emerging and re-emerging ZIKV outbreaks, whether caused by Ae. aegypti or Ae. albopictus or by the Asian or African ZIKV.

Human muscle cells sensitivity to chikungunya virus infection relies on their glycolysis activity and differentiation stage

Changes to our environment have led to the emergence of human pathogens such as chikungunya virus. Chikungunya virus infection is today a major public health concern. It is a debilitating chronic disease impeding patients' mobility, affecting millions of people. Disease development relies on skeletal muscle infection. The importance of skeletal muscle in chikungunya virus infection led to the hypothesis that it could serve as a viral reservoir and could participate to virus persistence. Here we questioned the interconnection between skeletal muscle cells metabolism, their differentiation stage and the infectivity of the chikungunya virus. We infected human skeletal muscle stem cells at different stages of differentiation with chikungunya virus to study the impact of their metabolism on virus production and inversely the impact of virus on cell metabolism. We observed that chikungunya virus infectivity is cell differentiation and metabolism-dependent. Chikungunya virus interferes with the cellular metabolism in quiescent undifferentiated and proliferative muscle cells. Moreover, activation of chikungunya infected quiescent muscle stem cells, induces their proliferation, increases glycolysis and amplifies virus production. Therefore, our results showed that Chikungunya virus infectivity and the antiviral response of skeletal muscle cells relies on their energetic metabolism and their differentiation stage. Then, muscle stem cells could serve as viral reservoir producing virus after their activation.

Viral Components Trafficking with(in) Extracellular Vesicles

The global public health burden exerted by viruses partially stems from viruses' ability to subdue host cells into creating an environment that promotes their multiplication (i.e., pro-viral). It has been discovered that viruses alter cell physiology by transferring viral material through extracellular vesicles (EVs), which serve as vehicles for intercellular communication. Here, we aim to provide a conceptual framework of all possible EV-virus associations and their resulting functions in infection output. First, we describe the different viral materials potentially associated with EVs by reporting that EVs can harbor entire virions, viral proteins and viral nucleic acids. We also delineate the different mechanisms underlying the internalization of these viral components into EVs. Second, we describe the potential fate of EV-associated viral material cargo by detailing how EV can circulate and target a naive cell once secreted. Finally, we itemize the different pro-viral strategies resulting from EV associations as the Trojan horse strategy, an alternative mode of viral transmission, an expansion of viral cellular tropism, a pre-emptive alteration of host cell physiology and an immunity decoy. With this conceptual overview, we aim to stimulate research on EV-virus interactions.

Prevalence and public health significance of rabies virus in bats in the North Region of Cameroon

BACKGROUND

Rabies is a zoonotic disease of all warm-blooded animals including humans. There is a paucity of data on the status of rabies in wild animals in Cameroon and the disease is endemic in the country with dogs being the main source of transmission. Bat habitats are widespread in Cameroon, but there is limited information on the prevalence of rabies in bats, and their role of as potential reservoirs of rabies virus.

METHODS

A cross sectional study was carried out to estimate the prevalence and to assess risk factors of rabies virus in bats in the North Region of Cameroon. A total of 212 bats belonging to three families (Pteropodidae, Vespertilionidae and Molossidae) and 5 species were sampled in 7 localities in the North Region of Cameroon and were tested for rabies virus antigen using direct Immunofluorescence Test (IFA).

RESULTS

Overall, 26.9% (57/212) of the bats collected showed an IFA positive reaction. The prevalence was significantly higher (P<0.05) in adult bats (33.3% (36/108)) compared to young individuals (20.2%; 21/104). The main risk factors identified in the study for human exposure to bats were gender (Male), religion (Christianity), localities (Babla and Lagdo), the practice of bat hunting, bat consumption, unawareness of bat rabies and cohabitation with bats in close proximity.

CONCLUSION

The study revealed the first evidence of Lyssavirus in bats in Cameroon. This finding showed that bat rabies are real and represents a potential public health concern in communities with bat habitats in the North Region of Cameroon. Enhancing the level of public awareness and health education on the potential of bats as reservoirs of Lyssavirus in Cameroon as well as the integration of the "One Health" approach for effective management of animal and human rabies should be emphasized.

Midgut transcriptomic responses to dengue and chikungunya viruses in the vectors Aedes albopictus and Aedes malayensis

Dengue (DENV) and chikungunya (CHIKV) viruses are among the most preponderant arboviruses. Although primarily transmitted through the bite of Aedes aegypti mosquitoes, Aedes albopictus and Aedes malayensis are competent vectors and have an impact on arbovirus epidemiology. Here, to fill the gap in our understanding of the molecular interactions between secondary vectors and arboviruses, we used transcriptomics to profile the whole-genome responses of A. albopictus to CHIKV and of A. malayensis to CHIKV and DENV at 1 and 4 days post-infection (dpi) in midguts. In A. albopictus, 1793 and 339 genes were significantly regulated by CHIKV at 1 and 4 dpi, respectively. In A. malayensis, 943 and 222 genes upon CHIKV infection, and 74 and 69 genes upon DENV infection were significantly regulated at 1 and 4 dpi, respectively. We reported 81 genes that were consistently differentially regulated in all the CHIKV-infected conditions, identifying a CHIKV-induced signature. We identified expressed immune genes in both mosquito species, using a de novo assembled midgut transcriptome for A. malayensis, and described the immune architectures. We found the JNK pathway activated in all conditions, generalizing its antiviral function to Aedines. Our comprehensive study provides insight into arbovirus transmission by multiple Aedes vectors.

Identification of the Tembusu Virus in Mosquitoes in Northern Thailand

Among emerging zoonotic pathogens, mosquito-borne viruses (MBVs) circulate between vertebrate animals and mosquitoes and represent a serious threat to humans via spillover from enzootic cycles to the human community. Active surveillance of MBVs in their vectors is therefore essential to better understand and prevent spillover and emergence, especially at the human-animal interface. In this study, we assessed the presence of MBVs using molecular and phylogenetic methods in mosquitoes collected along an ecological gradient ranging from rural urbanized areas to highland forest areas in northern Thailand. We have detected the presence of insect specific flaviviruses in our samples, and the presence of the emerging zoonotic Tembusu virus (TMUV). Reported for the first time in 1955 in Malaysia, TMUV remained for a long time in the shadow of other flaviviruses such as dengue virus or the Japanese encephalitis virus. In this study, we identified two new TMUV strains belonging to cluster 3, which seems to be endemic in rural areas of Thailand and highlighted the genetic specificities of this Thai cluster. Our results show the active circulation of this emerging flavivirus in Thailand and the need for continuous investigation on this poorly known but threatening virus in Asia.

Emerging and re-emerging zoonotic viral diseases in Southeast Asia: One Health challenge

The ongoing significant social, environmental, and economic changes in Southeast Asia (SEA) make the region highly vulnerable to the emergence and re-emergence of zoonotic viral diseases. In the last century, SEA has faced major viral outbreaks with great health and economic impact, including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), arboviruses, highly pathogenic avian influenza (H5N1), and Severe Acute Respiratory Syndrome (SARS-CoV); and so far, imported cases of Middle East Respiratory Syndrome Coronavirus (MERS-CoV). Given the recent challenging experiences in addressing emerging zoonotic diseases, it is necessary to redouble efforts to effectively implement the "One Health" initiative in the region, which aims to strengthen the human-animal-plant-environment interface to better prevent, detect and respond to health threats while promoting sustainable development. This review provides an overview of important emerging and re-emerging zoonotic viral diseases in SEA, with emphasis on the main drivers behind their emergency, the epidemiological situation from January 2000 to October 2022, and the importance of One Health to promote improved intervention strategies.

The anti-immune dengue subgenomic flaviviral RNA is present in vesicles in mosquito saliva and is associated with increased infectivity

Mosquito transmission of dengue viruses to humans starts with infection of skin resident cells at the biting site. There is great interest in identifying transmission-enhancing factors in mosquito saliva in order to counteract them. Here we report the discovery of high levels of the anti-immune subgenomic flaviviral RNA (sfRNA) in dengue virus 2-infected mosquito saliva. We established that sfRNA is present in saliva using three different methods: northern blot, RT-qPCR and RNA sequencing. We next show that salivary sfRNA is protected in detergent-sensitive compartments, likely extracellular vesicles. In support of this hypothesis, we visualized viral RNAs in vesicles in mosquito saliva and noted a marked enrichment of signal from 3'UTR sequences, which is consistent with the presence of sfRNA. Furthermore, we show that incubation with mosquito saliva containing higher sfRNA levels results in higher virus infectivity in a human hepatoma cell line and human primary dermal fibroblasts. Transfection of 3'UTR RNA prior to DENV2 infection inhibited type I and III interferon induction and signaling, and enhanced viral replication. Therefore, we posit that sfRNA present in salivary extracellular vesicles is delivered to cells at the biting site to inhibit innate immunity and enhance dengue virus transmission.

Evaluation of cutaneous immune response in a controlled human in vivo model of mosquito bites

Mosquito-borne viruses are a growing global threat. Initial viral inoculation occurs in the skin via the mosquito 'bite', eliciting immune responses that shape the establishment of infection and pathogenesis. Here we assess the cutaneous innate and adaptive immune responses to controlled Aedes aegypti feedings in humans living in Aedes-endemic areas. In this single-arm, cross-sectional interventional study (trial registration #NCT04350905), we enroll 30 healthy adult participants aged 18 to 45 years of age from Cambodia between October 2020 and January 2021. We perform 3-mm skin biopsies at baseline as well as 30 min, 4 h, and 48 h after a controlled feeding by uninfected Aedes aegypti mosquitos. The primary endpoints are measurement of changes in early and late innate responses in bitten vs unbitten skin by gene expression profiling, immunophenotyping, and cytokine profiling. The results reveal induction of neutrophil degranulation and recruitment of skin-resident dendritic cells and M2 macrophages. As the immune reaction progresses T cell priming and regulatory pathways are upregulated along with a shift to T_h2-driven responses and CD8⁺ T cell activation. Stimulation of participants' bitten skin cells with Aedes aegypti salivary gland extract results in reduced pro-inflammatory cytokine production. These results identify key immune genes, cell types, and pathways in the human response to mosquito bites and can be leveraged to inform and develop novel therapeutics and vector-targeted vaccine candidates to interfere with vector-mediated disease.

Internal RNA 2′O-methylation in the HIV-1 genome counteracts ISG20 nuclease-mediated antiviral effect

RNA 2′O-methylation is a ‘self’ epitranscriptomic modification allowing discrimination between host and pathogen. Indeed, human immunodeficiency virus 1 (HIV-1) induces 2′O-methylation of its genome by recruiting the cellular FTSJ3 methyltransferase, thereby impairing detection by RIG-like receptors. Here, we show that RNA 2′O-methylations interfere with the antiviral activity of interferon-stimulated gene 20-kDa protein (ISG20). Biochemical experiments showed that ISG20-mediated degradation of 2′O-methylated RNA pauses two nucleotides upstream of and at the methylated residue. Structure-function analysis indicated that this inhibition is due to steric clash between ISG20 R53 and D90 residues and the 2′O-methylated nucleotide. We confirmed that hypomethylated HIV-1 genomes produced in FTSJ3-KO cells were more prone to in vitro degradation by ISG20 than those produced in cells expressing FTSJ3. Finally, we found that reverse-transcription of hypomethylated HIV-1 was impaired in T cells by interferon-induced ISG20, demonstrating the direct antagonist effect of 2′O-methylation on ISG20-mediated antiviral activity.

Characterization of dengue virus 3'UTR RNA binding proteins in mosquitoes reveals that AeStaufen reduces subgenomic flaviviral RNA in saliva

Dengue viruses (DENV) are expanding global pathogens that are transmitted through the bite of mosquitoes, mostly Aedes aegypti. As RNA viruses, DENV rely on RNA-binding proteins (RBPs) to complete their life cycle. Alternatively, RBPs can act as restriction factors that prevent DENV multiplication. While the importance of RBPs is well-supported in humans, there is a dearth of information about their influence on DENV transmission by mosquitoes. Such knowledge could be harnessed to design novel, effective interventions against DENV. Here, we successfully adapted RNA-affinity chromatography coupled with mass spectrometry-a technique initially developed in mammalian cells-to identify RBPs in Ae. aegypti cells. We identified fourteen RBPs interacting with DENV serotype 2 3'UTR, which is involved in the viral multiplication and produces subgenomic flaviviral RNA (sfRNA). We validated the RNA affinity results for two RBPs by confirming that AePur binds the 3'UTR, whereas AeStaufen interacts with both 3'UTR and sfRNA. Using in vivo functional evaluation, we determined that RBPs like AeRan, AeExoRNase, and AeRNase have pro-viral functions, whereas AeGTPase, AeAtu, and AePur have anti-viral functions in mosquitoes. Furthermore, we showed that human and mosquito Pur homologs have a shared affinity to DENV2 RNA, although the anti-viral effect is specific to the mosquito protein. Importantly, we revealed that AeStaufen mediates a reduction of gRNA and sfRNA copies in several mosquito tissues, including the salivary glands and that AeStaufen-mediated sfRNA reduction diminishes the concentration of transmission-enhancing sfRNA in saliva, thereby revealing AeStaufen's role in DENV transmission. By characterizing the first RBPs that associate with DENV2 3'UTR in mosquitoes, our study unravels new pro- and anti-viral targets for the design of novel therapeutic interventions as well as provides foundation for studying the role of RBPs in virus-vector interactions.

Longitudinal Survey of Coronavirus Circulation and Diversity in Insectivorous Bat Colonies in Zimbabwe

Background: Studies have linked bats to outbreaks of viral diseases in human populations such as SARS-CoV-1 and MERS-CoV and the ongoing SARS-CoV-2 pandemic. Methods: We carried out a longitudinal survey from August 2020 to July 2021 at two sites in Zimbabwe with bat–human interactions: Magweto cave and Chirundu farm. A total of 1732 and 1866 individual bat fecal samples were collected, respectively. Coronaviruses and bat species were amplified using PCR systems. Results: Analysis of the coronavirus sequences revealed a high genetic diversity, and we identified different sub-viral groups in the Alphacoronavirus and Betacoronavirus genus. The established sub-viral groups fell within the described Alphacoronavirus sub-genera: Decacovirus, Duvinacovirus, Rhinacovirus, Setracovirus and Minunacovirus and for Betacoronavirus sub-genera: Sarbecoviruses, Merbecovirus and Hibecovirus. Our results showed an overall proportion for CoV positive PCR tests of 23.7% at Chirundu site and 16.5% and 38.9% at Magweto site for insectivorous bats and Macronycteris gigas, respectively. Conclusions: The higher risk of bat coronavirus exposure for humans was found in December to March in relation to higher viral shedding peaks of coronaviruses in the parturition, lactation and weaning months of the bat populations at both sites. We also highlight the need to further document viral infectious risk in human/domestic animal populations surrounding bat habitats in Zimbabwe.

Phylogenetic relationship between the endosymbiont "Candidatus Riesia pediculicola" and its human louse host

Background

The human louse (Pediculus humanus) is a haematophagous ectoparasite that is intimately related to its host. It has been of great public health concern throughout human history. This louse has been classified into six divergent mitochondrial clades (A, D, B, F, C and E). As with all haematophagous lice, P. humanus directly depends on the presence of a bacterial symbiont, known as “Candidatus Riesia pediculicola”, to complement their unbalanced diet. In this study, we evaluated the codivergence of human lice around the world and their endosymbiotic bacteria. Using molecular approaches, we targeted lice mitochondrial genes from the six diverged clades and Candidatus Riesia pediculicola housekeeping genes.

Methods

The mitochondrial cytochrome b gene (cytb) of lice was selected for molecular analysis, with the aim to identify louse clade. In parallel, we developed four PCR primer pairs targeting three housekeeping genes of Candidatus Riesia pediculicola: ftsZ, groEL and two regions of the rpoB gene (rpoB-1 and rpoB-2).

Results

The endosymbiont phylogeny perfectly mirrored the host insect phylogeny using the ftsZ and rpoB-2 genes, in addition to showing a significant co-phylogenetic congruence, suggesting a strict vertical transmission and a host–symbiont co-speciation following the evolutionary course of the human louse.

Conclusion

Our results unequivocally indicate that louse endosymbionts have experienced a similar co-evolutionary history and that the human louse clade can be determined by their endosymbiotic bacteria.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05203-z.

Detection and genetic diversity of Mopeia virus in Mastomys natalensis from different habitats in the Limpopo National Park, Mozambique

Mammarenaviruses have been a growing concern for public health in Africa since the 1970s when Lassa virus cases in humans were first described in west Africa. In southern Africa, a single outbreak of Lujo virus was reported to date in South Africa in 2008 with a case fatality rate of 80%. The natural reservoir of Lassa virus is Mastomys natalensis while for the Lujo virus the natural host has yet to be identified. Mopeia virus was described for the first time in M. natalensis in the central Mozambique in 1977 but few studies have been conducted in the region. In this study, rodents were trapped between March and November 2019in villages, croplands fields and mopane woodland forest. The aim was to assess the potential circulation and to evaluate the genetic diversity of mammarenaviruses in M. natalensis trapped in the Limpopo National Park and its buffer zone in Massingir district, Mozambique. A total of 534 M. natalensis were screened by RT-PCR and the overall proportion of positive individuals was 16.9%. No significant differences were detected between the sampled habitats (χ2 = 0.018; DF = 1; p = 0.893). The Mopeia virus (bootstrap value 91%) was the Mammarenavirus circulating in the study area sites, forming a specific sub-clade with eight different sub-clusters. We concluded that Mopeia virus circulates in all habitats investigated and it forms a different sub-clade to the one reported in central Mozambique in 1977.

Lipid Interactions Between Flaviviruses and Mosquito Vectors

Mosquito-borne flaviviruses, such as dengue (DENV), Zika (ZIKV), yellow fever (YFV), West Nile (WNV), and Japanese encephalitis (JEV) viruses, threaten a large part of the human populations. In absence of therapeutics and effective vaccines against each flaviviruses, targeting viral metabolic requirements in mosquitoes may hold the key to new intervention strategies. Development of metabolomics in the last decade opened a new field of research: mosquito metabolomics. It is now clear that flaviviruses rely on mosquito lipids, especially phospholipids, for their cellular cycle and propagation. Here, we review the biosyntheses of, biochemical properties of and flaviviral interactions with mosquito phospholipids. Phospholipids are structural lipids with a polar headgroup and apolar acyl chains, enabling the formation of lipid bilayer that form plasma- and endomembranes. Phospholipids are mostly synthesized through the de novo pathway and remodeling cycle. Variations in headgroup and acyl chains influence phospholipid physicochemical properties and consequently the membrane behavior. Flaviviruses interact with cellular membranes at every step of their cellular cycle. Recent evidence demonstrates that flaviviruses reconfigure the phospholipidome in mosquitoes by regulating phospholipid syntheses to increase virus multiplication. Identifying the phospholipids involved and understanding how flaviviruses regulate these in mosquitoes is required to design new interventions.

High resolution proteomics of Aedes aegypti salivary glands infected with either dengue, Zika or chikungunya viruses identify new virus specific and broad antiviral factors

Arboviruses such as dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV) viruses infect close to half a billion people per year, and are primarily transmitted through Aedes aegypti bites. Infection-induced changes in mosquito salivary glands (SG) influence transmission by inducing antiviral immunity, which restricts virus replication in the vector, and by altering saliva composition, which influences skin infection. Here, we profiled SG proteome responses to DENV serotype 2 (DENV2), ZIKV and CHIKV infections by using high-resolution isobaric-tagged quantitative proteomics. We identified 218 proteins with putative functions in immunity, blood-feeding or related to the cellular machinery. We observed that 58, 27 and 29 proteins were regulated by DENV2, ZIKV and CHIKV infections, respectively. While the regulation patterns were mostly virus-specific, we separately depleted four uncharacterized proteins that were upregulated by all three viral infections to determine their effects on these viral infections. Our study suggests that gamma-interferon responsive lysosomal thiol-like (GILT-like) has an anti-ZIKV effect, adenosine deaminase (ADA) has an anti-CHIKV effect, salivary gland surface protein 1 (SGS1) has a pro-ZIKV effect and salivary gland broad-spectrum antiviral protein (SGBAP) has an antiviral effect against all three viruses. The comprehensive description of SG responses to three global pathogenic viruses and the identification of new restriction factors improves our understanding of the molecular mechanisms influencing transmission.

Favipiravir Inhibits Mayaro Virus Infection in Mice

Mayaro virus (MAYV) is an emergent alphavirus that causes MAYV fever. It is often associated with debilitating symptoms, particularly arthralgia and myalgia. MAYV infection is becoming a considerable health issue that, unfortunately, lacks a specific antiviral treatment. Favipiravir, a broad-spectrum antiviral drug, has recently been shown to exert anti-MAYV activity in vitro. In the present study, the potential of Favipiravir to inhibit MAYV replication in an in vivo model was evaluated. Immunocompetent mice were orally administrated 300 mg/kg/dose of Favipiravir at pre-, concurrent-, or post-MAYV infection. The results showed a significant reduction in infectious viral particles and viral RNA transcripts in the tissues and blood of the pre- and concurrently treated infected mice. A significant reduction in the presence of both viral RNA transcript and infectious viral particles in the tissue and blood of pre- and concurrently treated infected mice was observed. By contrast, Favipiravir treatment post-MAYV infection did not result in a reduction in viral replication. Interestingly, Favipiravir strongly decreased the blood levels of the liver disease markers aspartate- and alanine aminotransferase in the pre- and concurrently treated MAYV-infected mice. Taken together, these results suggest that Favipiravir is a potent antiviral drug when administered in a timely manner.

Human host genetics and susceptibility to ZIKV infection

Managing emerging infectious diseases is a current challenge in the fields of microbiology and epidemiology. Indeed, among other environmental and human-related factors, climate change and global warming favor the emergence of new pathogens. The recent Zika virus (ZIKV) epidemic, of which the large and rapid spread surprised the scientific community, is a reminder of the importance to study viruses currently responsible for sporadic infections. Increasing our knowledge of key factors involved in emerging infections is essential to implement specific monitoring that can be oriented according to the pathogen, targeted population, or at-risk environment. Recent technological developments, such as high-throughput sequencing, genome-wide association studies and CRISPR screenings have allowed the identification of human single nucleotide polymorphisms (SNPs) involved in infectious disease outcome. This review focuses on the human genetic host factors that have been identified and shown to be associated with the pathogenesis of ZIKV infection and candidate SNP targets.

Delineating the Role of Aedes aegypti ABC Transporter Gene Family during Mosquito Development and Arboviral Infection via Transcriptome Analyses

Aedes aegypti acts as a vector for several arboviral diseases that impose a major socio-economic burden. Moreover, the absence of a vaccine against these diseases and drug resistance in mosquitoes necessitates the development of new control strategies for vector-borne diseases. ABC transporters that play a vital role in immunity and other cellular processes in different organisms may act as non-canonical immune molecules against arboviruses, however, their role in mosquito immunity remains unexplored. This study comprehensively analyzed various genetic features of putative ABC transporters and classified them into A-H subfamilies based on their evolutionary relationships. Existing RNA-sequencing data analysis indicated higher expression of cytosolic ABC transporter genes (E & F Subfamily) throughout the mosquito development, while members of other subfamilies exhibited tissue and time-specific expression. Furthermore, comparative gene expression analysis from the microarray dataset of mosquito infected with dengue, yellow fever and West Nile viruses revealed 31 commonly expressed ABC transporters suggesting a potentially conserved transcriptomic signature of arboviral infection. Among these, only a few transporters of ABCA, ABCC and ABCF subfamily were upregulated, while most were downregulated. This indicates the possible involvement of ABC transporters in mosquito immunity.

Chikungunya and Zika Viruses: Co-Circulation and the Interplay between Viral Proteins and Host Factors

Chikungunya and Zika viruses, both transmitted by mosquito vectors, have globally re-emerged over for the last 60 years and resulted in crucial social and economic concerns. Presently, there is no specific antiviral agent or vaccine against these debilitating viruses. Understanding viral-host interactions is needed to develop targeted therapeutics. However, there is presently limited information in this area. In this review, we start with the updated virology and replication cycle of each virus. Transmission by similar mosquito vectors, frequent co-circulation, and occurrence of co-infection are summarized. Finally, the targeted host proteins/factors used by the viruses are discussed. There is an urgent need to better understand the virus-host interactions that will facilitate antiviral drug development and thus reduce the global burden of infections caused by arboviruses.

Mayaro Virus Infects Human Brain Cells and Induces a Potent Antiviral Response in Human Astrocytes

Mayaro virus (MAYV) and chikungunya virus (CHIKV) are known for their arthrotropism, but accumulating evidence shows that CHIKV infections are occasionally associated with serious neurological complications. However, little is known about the capacity of MAYV to invade the central nervous system (CNS). We show that human neural progenitors (hNPCs), pericytes and astrocytes are susceptible to MAYV infection, resulting in the production of infectious viral particles. In primary astrocytes, MAYV, and to a lesser extent CHIKV, elicited a strong antiviral response, as demonstrated by an increased expression of several interferon-stimulated genes, including ISG15, MX1 and OAS2. Infection with either virus led to an enhanced expression of inflammatory chemokines, such as CCL5, CXCL10 and CXCL11, whereas MAYV induced higher levels of IL-6, IL-12 and IL-15 in these cells. Moreover, MAYV was more susceptible than CHIKV to the antiviral effects of both type I and type II interferons. Taken together, this study shows that although MAYV and CHIKV are phylogenetically related, they induce different types of antiviral responses in astrocytes. This work is the first to evaluate the potential neurotropism of MAYV and shows that brain cells and particularly astrocytes and hNPCs are permissive to MAYV, which, consequently, could lead to MAYV-induced neuropathology.

Cancer and mosquitoes - An unsuspected close connection

Cancer is a major public health issue and represents a significant burden in countries with different levels of economic wealth. In parallel, mosquito-borne infectious diseases represent a growing problem causing significant morbidity and mortality worldwide. Acknowledging that these two concerns are both globally distributed, it is essential to investigate whether they have a reciprocal connection that can fuel their respective burdens. Unfortunately, very few studies have examined the link between these two threats. This review provides an overview of the possible links between mosquitoes, mosquito-borne infectious diseases and cancer. We first focus on the impact of mosquitoes on carcinogenesis in humans including the transmission of oncogenic pathogens through mosquitoes, the immune reactions following mosquito bites, the presence of non-oncogenic mosquito-borne pathogens, and the direct transmission of cancer cells. The second part of this review deals with the direct or indirect consequences of cancer in humans on mosquito behaviour. Thirdly, we discuss the potential impacts that natural cancers in mosquitoes can have on their life history traits and therefore on their vector capacity. Finally, we discuss the most promising research avenues on this topic and the integrative public health strategies that could be envisioned in this context.

Vector Competence for Dengue-2 Viruses Isolated from Patients with Different Disease Severity

Dynamics of dengue serotype 2 virus isolated from patients with different disease severity, namely flu-like classic dengue fever (DF) and dengue shock syndrome (DSS) were studied in its mosquito vector Aedes aegypti. We compared isolate infectivity and vector competence (VC) among thirty two A. aegypti-viral isolate pairs. Mosquito populations from high dengue incidence area exhibited overall greater VC than those from low dengue incidence area at 58.1% and 52.5%, respectively. On the other hand, the overall infection rates for the isolates ThNR2/772 (DF, 62.3%) and ThNR2/391 (DSS, 60.9%), were significantly higher than those for isolates ThNR2/406 (DF, 55.2%) and ThNR2/479 (DSS, 54.8%). These results suggest that the efficacy of dengue virus circulation was likely to vary according to the combination between the virus strains and origin of the mosquito strains, and this may have epidemiologic implications toward the incidence of flu-like classic dengue fever (DF) and dengue shock syndrome (DSS).

Mayaro Virus Pathogenesis and Transmission Mechanisms

Mayaro virus (MAYV), isolated for the first time in Trinidad and Tobago, has captured the attention of public health authorities worldwide following recent outbreaks in the Americas. It has a propensity to be exported outside its original geographical range, because of the vast distribution of its vectors. Moreover, most of the world population is immunologically naïve with respect to infection with MAYV which makes this virus a true threat. The recent invasion of several countries by Aedesalbopictus underscores the risk of potential urban transmission of MAYV in both tropical and temperate regions. In humans, the clinical manifestations of MAYV disease range from mild fever, rash, and joint pain to arthralgia. In the absence of a licensed vaccine and clinically proven therapeutics against Mayaro fever, prevention focuses mainly on household mosquito control. However, as demonstrated for other arboviruses, mosquito control is rather inefficient for outbreak management and alternative approaches to contain the spread of MAYV are therefore necessary. Despite its strong epidemic potential, little is currently known about MAYV. This review addresses various aspects of MAYV, including its epidemiology, vector biology, mode of transmission, and clinical complications, as well as the latest developments in MAYV diagnosis.

JNK pathway restricts DENV2, ZIKV and CHIKV infection by activating complement and apoptosis in mosquito salivary glands

Arbovirus infection of Aedes aegypti salivary glands (SGs) determines transmission. However, there is a dearth of knowledge on SG immunity. Here, we characterized SG immune response to dengue, Zika and chikungunya viruses using high-throughput transcriptomics. We also describe a transcriptomic response associated to apoptosis, blood-feeding and lipid metabolism. The three viruses differentially regulate components of Toll, Immune deficiency (IMD) and c-Jun N- terminal Kinase (JNK) pathways. However, silencing of the Toll and IMD pathway components showed variable effects on SG infection by each virus. In contrast, regulation of the JNK pathway produced consistent responses in both SGs and midgut. Infection by the three viruses increased with depletion of the activator Kayak and decreased with depletion of the negative regulator Puckered. Virus-induced JNK pathway regulates the complement factor, Thioester containing protein-20 (TEP20), and the apoptosis activator, Dronc, in SGs. Individual and co-silencing of these genes demonstrate their antiviral effects and that both may function together. Co-silencing either TEP20 or Dronc with Puckered annihilates JNK pathway antiviral effect. Upon infection in SGs, TEP20 induces antimicrobial peptides (AMPs), while Dronc is required for apoptosis independently of TEP20. In conclusion, we revealed the broad antiviral function of JNK pathway in SGs and showed that it is mediated by a TEP20 complement and Dronc-induced apoptosis response. These results expand our understanding of the immune arsenal that blocks arbovirus transmission.

Arboviral diseases caused by dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV) viruses are responsible for large number of death and debilitation around the world. These viruses are transmitted to humans by the mosquito vector, Aedes aegypti. During the bites, infected salivary glands (SGs) release saliva containing viruses, which initiate human infection. As the tissue where transmitted viruses are produced, SG infection is a key determinant of transmission. To bridge the knowledge gap in vector-virus molecular interactions in SGs, we describe the transcriptome after DENV, ZIKV and CHIKV infection using RNA-sequencing and characterized the immune response in this tissue. Our study reveals the broad antiviral function of c-Jun N-terminal kinase (JNK) pathway against DENV, ZIKV and CHIKV in SGs. We further show that it is mediated by the complement system and apoptosis, identifying the mechanism. Our study adds the JNK pathway to the immune arsenal that can be harnessed to engineer refractory vectors.

Aedes Mosquito Salivary Components and Their Effect on the Immune Response to Arboviruses

Vector-borne diseases are responsible for over a billion infections each year and nearly one million deaths. Mosquito-borne dengue virus, West Nile, Japanese encephalitis, Zika, Chikungunya, and Rift Valley Fever viruses constitute major public health problems in regions with high densities of arthropod vectors. During the initial step of the transmission cycle, vector, host, and virus converge at the bite site, where local immune cells interact with the vector's saliva. Hematophagous mosquito saliva is a mixture of bioactive components known to modulate vertebrate hemostasis, immunity, and inflammation during the insect's feeding process. The capacity of mosquito saliva to modulate the host immune response has been well-studied over the last few decades and has led to the consensus that the presence of saliva is linked to the enhancement of virus transmission, host susceptibility, disease progression, viremia levels, and mortality. We review some of the major aspects of the interactions between mosquito saliva and the host immune response that may be useful for future studies on the control of arboviruses.

The role of innate immunity in the protection conferred by a bacterial infection against cancer: study of an invertebrate model

All multicellular organisms are exposed to a diversity of infectious agents and to the emergence and proliferation of malignant cells. The protection conferred by some infections against cancer has been recently linked to the production of acquired immunity effectors such as antibodies. However, the evolution of innate immunity as a mechanism to prevent cancer and how it is jeopardized by infections remain poorly investigated. Here, we explored this question by performing experimental infections in two genetically modified invertebrate models (Drosophila melanogaster) that develop invasive or non-invasive neoplastic brain tumors. After quantifying tumor size and antimicrobial peptide gene expression, we found that Drosophila larvae infected with a naturally occurring bacterium had smaller tumors compared to controls and to fungus-infected larvae. This was associated with the upregulation of genes encoding two antimicrobial peptides-diptericin and drosomycin-that are known to be important mediators of tumor cell death. We further confirmed that tumor regression upon infection was associated with an increase in tumor cell death. Thus, our study suggests that infection could have a protective role through the production of antimicrobial peptides that increase tumor cell death. Finally, our study highlights the need to understand the role of innate immune effectors in the complex interactions between infections and cancer cell communities in order to develop innovative cancer treatment strategies.

Highly Efficient Vertical Transmission for Zika Virus in Aedes aegypti after Long Extrinsic Incubation Time

While the Zika virus (ZIKV) 2014-2017 pandemic has subsided, there remains active transmission. Apart from horizontal transmission to humans, the main vector Aedes aegypti can transmit the virus vertically from mother to offspring. Large variation in vertical transmission (VT) efficiency between studies indicates the influence of parameters, which remain to be characterized. To determine the roles of extrinsic incubation time and gonotrophic cycle, we deployed an experimental design that quantifies ZIKV in individual progeny and larvae. We observed an early infection of ovaries that exponentially progressed. We quantified VT rate, filial infection rate, and viral load per infected larvae at 10 days post oral infection (d.p.i.) on the second gonotrophic cycle and at 17 d.p.i. on the second and third gonotrophic cycle. As compared to previous reports that studied pooled samples, we detected a relatively high VT efficiency from 1.79% at 10 d.p.i. and second gonotrophic cycle to 66% at 17 d.p.i. and second gonotrophic cycle. At 17 d.p.i., viral load largely varied and averaged around 800 genomic RNA (gRNA) copies. Longer incubation time and fewer gonotrophic cycles promoted VT. These results shed light on the mechanism of VT, how environmental conditions favor VT, and whether VT can maintain ZIKV circulation.

Dengue virus reduces AGPAT1 expression to alter phospholipids and enhance infection in Aedes aegypti

More than half of the world population is at risk of dengue virus (DENV) infection because of the global distribution of its mosquito vectors. DENV is an envelope virus that relies on host lipid membranes for its life-cycle. Here, we characterized how DENV hijacks the mosquito lipidome to identify targets for novel transmission-blocking interventions. To describe metabolic changes throughout the mosquito DENV cycle, we deployed a Liquid chromatography-high resolution mass spectrometry (LC-HRMS) workflow including spectral similarity annotation in cells, midguts and whole mosquitoes at different times post infection. We revealed a major aminophospholipid reconfiguration with an overall early increase, followed by a reduction later in the cycle. We phylogenetically characterized acylglycerolphosphate acyltransferase (AGPAT) enzyme isoforms to identify those that catalyze a rate-limiting step in phospholipid biogenesis, the acylation of lysophosphatidate to phosphatidate. We showed that DENV infection decreased AGPAT1, but did not alter AGPAT2 expression in cells, midguts and mosquitoes. Depletion of either AGPAT1 or AGPAT2 increased aminophospholipids and partially recapitulated DENV-induced reconfiguration before infection in vitro. However, only AGPAT1 depletion promoted infection by maintaining high aminophospholipid concentrations. In mosquitoes, AGPAT1 depletion also partially recapitulated DENV-induced aminophospholipid increase before infection and enhanced infection by maintaining high aminophospholipid concentrations. These results indicate that DENV inhibition of AGPAT1 expression promotes infection by increasing aminophospholipids, as observed in the mosquito's early DENV cycle. Furthermore, in AGPAT1-depleted mosquitoes, we showed that enhanced infection was associated with increased consumption/redirection of aminophospholipids. Our study suggests that DENV regulates aminophospholipids, especially phosphatidylcholine and phosphatidylethanolamine, by inhibiting AGPAT1 expression to increase aminophospholipid availability for virus multiplication.

Next-Generation Sequencing on Insectivorous Bat Guano: An Accurate Tool to Identify Arthropod Viruses of Potential Agricultural Concern

Viruses belonging to the Dicistroviridae family have attracted a great deal of attention from scientists owing to their negative impact on agricultural economics, as well as their recent identification as potential aetiological agents of febrile illness in human patients. On the other hand, some Dicistroviruses are also studied for their potential biopesticide properties. To date, Dicistrovirus characterized in African mainland remain scarce. By using High-Throughput Sequencing technology on insectivorous bat faeces (Hipposideros Caffer) sampled in a cave used by humans to collect bat guano (bat manure) as fertilizer in Zimbabwe, we characterized the full-length sequences of three Dicistrovirus belonging to the Cripavirus and Aparavirus genus: Big Sioux River Virus-Like (BSRV-Like), Acute Bee Paralysis Virus (ABPV), and Aphid Lethal Paralysis Virus (ALPV). Phylogenetic analyses of ORF-1 and ORF-2 genes showed a complex evolutionary history between BSRV and close viruses, as well as for the Aparavirus genus. Herewith, we provide the first evidence of the presence of Dicistrovirus in Zimbabwe and highlight the need to further document the impact of such viruses on crops, as well as in beekeeping activities in Zimbabwe which represent a crucial source of income for Zimbabwean people.

Increased Mosquito Midgut Infection by Dengue Virus Recruitment of Plasmin Is Blocked by an Endogenous Kazal-type Inhibitor

Dengue symptoms include alteration of blood coagulation and fibrinolysis, causing severe hemorrhage and death. Here, we demonstrate that higher concentration of plasmin, the human fibrinolytic factor, in blood meal enhances dengue virus (DENV) infection in mosquito midgut and dissemination in mosquitoes. We also show that mosquitoes express a plasmin-selective Kazal-type inhibitor (AaTI) in the midgut to inhibit plasmin proteolysis and revert the enhanced infection. Using bio-layer interferometry, we show that DENV, plasmin, and AaTI interact to form a tripartite complex. Eventually, plasmin increases midgut internalization of dextran molecules and this is reverted by AaTI. Our study demonstrates that (1) DENV recruits plasmin to increase local proteolytic activity in the midgut, thus degrading the glycocalyx and enhancing DENV internalization and (2) AaTI can act as a transmission-blocking agent by inhibiting plasmin proteolysis. Our results indicate that dengue pathogenesis enhances DENV fitness by increasing its infectivity to mosquitoes.

Differential Susceptibility and Innate Immune Response of Aedes aegypti and Aedes albopictus to the Haitian Strain of the Mayaro Virus

Mayaro (MAYV) is an emerging arthropod-borne virus belonging to the Alphavirus genus of the Togaviridae family. Although forest-dwelling Haemagogus mosquitoes have been considered as its main vector, the virus has also been detected in circulating Aedes ssp mosquitoes. Here we assess the susceptibility of Aedes aegypti and Aedes albopictus to infection with MAYV and their innate immune response at an early stage of infection. Aedes albopictus was more susceptible to infection with MAYV than Ae. aegypti. Analysis of transcript levels of twenty immunity-related genes by real-time PCR in the midgut of both mosquitoes infected with MAYV revealed increased expression of several immune genes, including CLIP-domain serine proteases, the anti-microbial peptides defensin A, E, cecropin E, and the virus inducible gene. The regulation of certain genes appeared to be Aedes species-dependent. Infection of Ae. aegypti with MAYV resulted in increased levels of myeloid differentiation2-related lipid recognition protein (ML26A) transcripts, as compared to Ae. albopictus. Increased expression levels of thio-ester-containing protein 22 (TEP22) and Niemann–Pick type C1 (NPC1) gene transcripts were observed in infected Ae. albopictus, but not Ae. aegypti. The differences in these gene expression levels during MAYV infection could explain the variation in susceptibility observed in both mosquito species.

Mayaro Virus Infects Human Chondrocytes and Induces the Expression of Arthritis-Related Genes Associated with Joint Degradation

Mayaro virus (MAYV) is an emerging arthritogenic alphavirus belonging to the Togaviridae family. Infection leads to a dengue-like illness accompanied by severe polyarthralgia. However, the molecular and cellular mechanisms of arthritis as a result of MAYV infection remain poorly understood. In the present study, we assess the susceptibility of human chondrocytes (HC), fibroblast-like synoviocytes and osteoblasts that are the major cell types involved in osteoarthritis, to infection with MAYV. We show that these cells are highly permissive to MAYV infection and that viral RNA copy number and viral titers increase over time in infected cells. Knowing that HC are the primary cells in articular cartilage and are essential for maintaining the cartilaginous matrix, gene expression studies were conducted in MAYV-infected primary HC using polymerase chain reaction (PCR) arrays. The infection of the latter cells resulted in an induction in the expression of several matrix metalloproteinases (MMP) including MMP1, MMP7, MMP8, MMP10, MMP13, MMP14 and MMP15 which could be involved in the destruction of articular cartilage. Infected HC were also found to express significantly increased levels of various IFN-stimulated genes and arthritogenic mediators such as TNF-α and IL-6. In conclusion, MAYV-infected primary HC overexpress arthritis-related genes, which may contribute to joint degradation and pathogenesis.

Phylogenetic analysis revealed the co-circulation of four dengue virus serotypes in Southern Thailand

Dengue fever is caused by dengue viruses (DENV) from the Flavivirus genus and is the most prevalent arboviral disease. DENV exists in four immunogenically distinct and genetically-related serotypes (DENV-1 to 4), each subdivided in genotypes. Despite the endemicity of all four DENV serotypes in Thailand, no prior study has characterized the circulation of DENV in the southern provinces of the country. To determine the genetic diversity of DENV circulating in Southern Thailand in 2015 and 2016, we investigated 46 viruses from 182 patients' sera confirmed positive for DENV by serological and Nested RT-PCR tests. Our dataset included 2 DENV-1, 20 DENV-2, 9 DENV-3 and 15 DENV-4. Phylogenetic analysis was performed on viral envelop sequences. This revealed that part of the identified genotypes from DENV-1 and DENV-4 had been predominant in Asia (genotype I for both serotypes), while genotype II for DENV-4 and the Cosmopolitan genotype DENV-2 were also circulating. Whereas DENV-3 genotype II had been predominantly detected in South East Asia during the previous decades, we found genotype III and genotype I in Southern Thailand. All DENV genotype identified in this study were closely related to contemporary strains circulating in Southeast Asian countries, emphasizing the regional circulation of DENV. These results provide new insights into the co-circulation of all four DENV serotypes in Southern Thailand, confirming the hyperendemicity of DENV in the region. These findings also suggest a new trend of dissemination for some DENV serotypes with a possible shift in genotype distribution; as recently observed in other Asian countries.

Interferon-inducible protein (IFI) 16 regulates Chikungunya and Zika virus infection in human skin fibroblasts

Chikungunya virus (CHIKV), a re-emerging infectious arbovirus, causes Chikungunya fever that is characterized by fever, skin rash, joint pain, arthralgia and occasionally death. Despite it has been described for 66 years already, neither potential vaccine nor a specific drug is available yet. During CHIKV infection, interferon type I signaling pathway is stimulated and releases hundreds of interferon stimulated genes (ISGs). Our previous study reported that IFI16, a member of ISGs, is up-regulated during CHIKV virus infection and the suppression of the gene resulted in increased virus replication. Furthermore, our group also found that inflammasome activation can inhibit CHIKV infection in human foreskin cells (HFF1). Concomitantly, it has been reported that IFI16 activates the inflammasome to suppress virus infection. Therefore, we have hypothesized that IFI16 could be involved in CHIKV infection. In this study, we confirmed the expression level of IFI16 by Western blotting analysis and found that IFI16 was up-regulated following CHIKV infection in both HFF1 and human embryonic kidney cells. We next investigated its antiviral activity and found that forced expression of IFI16 completely restricted CHIKV infection while endogenous silencing of the gene markedly increased virus replication. Furthermore, we have discovered that IFI16 inhibited CHIKV replication, at least, in cell-to-cell transmission as well as the diffusion step. Interestingly, IFI16 also exerted its antiviral activity against Zika virus (ZIKV) infection, the global threat re-emerging virus can cause microcephaly in humans. Taken together, this study provides the first evidence of an antivirus activity of IFI16 during in vitro arbovirus infection, thus expanding its antiviral spectrum that paves the way to further development of antiviral drugs and vaccines.

Inhibition of N-myristoyltransferase1 affects dengue virus replication

Dengue virus (DENV) causes dengue fever, a self‐limiting disease that could be fatal due to serious complications. No specific treatment is currently available and the preventative vaccine is only partially protective. To develop a potential drug target for dengue fever, we need to understand its biology and pathogenesis thoroughly. N‐myristoyltransferase (NMT) is an N‐terminal protein lipidation enzyme that catalyzes the covalent cotranslational attachment of fatty acids to the amino‐terminal glycine residue of a number of proteins, leading to the modulation of various signaling molecules. In this study, we investigated the interaction of dengue viral proteins with host NMT and its subsequent effect on DENV. Our bioinformatics, molecular docking, and far‐western blotting analyses demonstrated the interaction of viral envelope protein (E) with NMT. The gene expression of NMT was strongly elevated in a dependent manner during the viral replication phase in dendritic cells. Moreover, NMT gene silencing significantly inhibited DENV replication in dendritic cells. Further studies investigating the target cell types of other host factors are suggested.

Zika virus differentially infects human neural progenitor cells according to their state of differentiation and dysregulates neurogenesis through the Notch pathway

Zika virus (ZIKV) is a mosquito-borne Flavivirus that causes Zika disease with particular neurological complications, including Guillain-Barré Syndrome and congenital microcephaly. Although ZIKV has been shown to directly infect human neural progenitor cells (hNPCs), thereby decreasing their viability and growth, it is as yet unknown which of the cellular pathways involved in the disruption of neurogenesis are affected following ZIKV infection. By comparing the effect of two ZIKV strains in vitro on hNPCs, the differentiation process of the latter cells was found to lead to a decreased susceptibility to infection and cell death induced by each of the ZIKV strains, which was associated with an earlier and stronger antiviral innate immune response in infected, differentiated hNPCs, as compared to undifferentiated cells. Moreover, ZIKV modulated, both in hNPCs and in vivo in fetal brain in an experimental mouse model, the expression of the Notch pathway which is involved in cellular proliferation, apoptosis and differentiation during neurogenesis. These results show that the differentiation state of hNPCs is a significant factor contributing to the outcome of ZIKV infection and furthermore suggest that ZIKV infection might initiate early activation of the Notch pathway resulting in an abnormal differentiation process, implicated in ZIKV-induced brain injury.

Monitoring arbovirus in Thailand: Surveillance of dengue, chikungunya and zika virus, with a focus on coinfections

Infections caused by arboviruses such as dengue virus (DENV), chikungunya virus (CHIKV), and Zika virus (ZIKV) frequently occur in tropical and subtropical regions. These three viruses are transmitted by Aedes (Ae.) aegypti and Ae. albopictus. In Thailand, the highest incidence of arbovirus infection and the high circulation of Aedes mosquito mainly occurs in the Southern provinces of the country. Few studies have focused on the incidence of co-infection of arboviruses in this region. In the present study, a cross-sectional study was conducted on a cohort of 182 febrile patients from three hospitals located in Southern Thailand. Surveillance of DENV, CHIKV and ZIKV was conducted from May to October 2016 during the rainy season. The serological analysis and molecular detection of arboviruses were performed by ELISA and multiplex RT-PCR respectively. The results demonstrated that 163 cases out of 182 patients (89.56%) were infected with DENV, with a predominance of DENV-2. Among these DENV positive cases, a co-infection with CHIKV for 6 patients (3.68%) and with ZIKV for 1 patient (0.61%) were found. 19 patients out of 182 were negative for arboviruses. This study provides evidence of co-infection of arboviruses in Southern Thailand and highlight the importance of testing DENV and other medically important arboviruses, such as CHIKV and ZIKV simultaneously.

Innate Immune Response of Primary Human Keratinocytes to West Nile Virus Infection and Its Modulation by Mosquito Saliva

West Nile Virus (WNV) is a flavivirus involved in many human infections worldwide. This arthropod-borne virus is directly co-inoculated with mosquito saliva through the epidermis and the dermis during blood meal. WNV starts replicating in the skin before migrating to the draining lymph node, leading to widespread viremia and in some cases to neurological symptoms. Skin is a complex organ composed of different cell types that together perform essential functions such as pathogen sensing, barrier maintenance and immunity. Keratinocytes, which represent 90% of the cells of the epidermis, are the organism's first line of defense, initiating innate immune response by recognizing pathogens through their pattern recognition receptors. Although WNV was previously known to replicate in human primary keratinocytes, the induced inflammatory response remains unknown. The aim of this study was first to characterize the inflammatory response of human primary keratinocytes to WNV infection and then, to assess the potential role of co-inoculated mosquito saliva on the keratinocyte immune response and viral replication. A type I and III interferon inflammatory response associated with an increase of IRF7 but not IRF3 mRNA expression, and dependent on infectious dose, was observed during keratinocyte infection with WNV. Expression of several interferon-stimulated gene mRNA was also increased at 24 h post-infection (p.i.); they included CXCL10 and interferon-induced proteins with tetratricopeptide repeats (IFIT)-2 sustained up until 48 h p.i. Moreover, WNV infection of keratinocyte resulted in a significant increase of pro-inflammatory cytokines (TNFα, IL-6) and various chemokines (CXCL1, CXCL2, CXCL8 and CCL20) expression. The addition of Aedes aegypti or Culex quinquefasciatus mosquito saliva, two vectors of WNV infection, to infected keratinocytes led to a decrease of inflammatory response at 24 h p.i. However, only Ae. Aegypti saliva adjunction induced modulation of viral replication. In conclusion, this work describes for the first time the inflammatory response of human primary keratinocytes to WNV infection and its modulation in presence of vector mosquito saliva. The effects of mosquito saliva assessed in this work could be involved in the early steps of WNV replication in skin promoting viral spread through the body.

Zika virus infection modulates the metabolomic profile of microglial cells

Zika virus (ZIKV) is an emerging arbovirus of the Flaviviridae family. Although infection with ZIKV generally leads to mild disease, its recent emergence in the Americas has been associated with an increase in the development of the Guillain-Barré syndrome in adults, as well as with neurological complications, in particular congenital microcephaly, in new-borns. To date, little information is available on neuroinflammation induced by ZIKV, notably in microglial cells in the context of their metabolic activity, a series of chemical transformations that are essential for their growth, reproduction, structural maintenance and environmental responses. Therefore, in the present study we investigated the metabolomic profile of ZIKV-infected microglia. Microglial cells were exposed to ZIKV at different time points and were analyzed by a Liquid Chromatography-High Resolution mass spectrometry-based metabolomic approach. The results show that ZIKV infection in microglia leads to modulation of the expression of numerous metabolites, including lysophospholipids, particulary Lysophosphatidylcholine, and phospholipids such as Phosphatidylcholine, Phosphatidylserine, Ceramide and Sphingomyelin, and carboxylicic acids as Undecanedioic and Dodecanedioic acid. Some of these metabolites are involved in neuronal differentiation, regulation of apoptosis, virion architecture and viral replication. ZIKV infection was associated with concomitant secretion of inflammatory mediators linked with central nervous system inflammation such as IL-6, TNF-α, IL-1β, iNOS and NO. It also resulted in the upregulation of the expression of the gene encoding CX3CR1, a chemokine receptor known to regulate functional synapse plasticity and signaling between microglial cells. These findings highlight an important role for microglia and their metabolites in the process of neuroinflammation that occurs during ZIKV pathogenesis.

Zika virus causes supernumerary foci with centriolar proteins and impaired spindle positioning

Zika virus (ZIKV) causes congenital microcephaly. Although ZIKV can impair cell cycle progression and provoke apoptosis, which probably contributes to disease aetiology through depletion of neural progenitor cells, additional cellular mechanisms may be important. Here, we investigated whether ZIKV infection alters centrosome number and spindle positioning, because such defects are thought to be at the root of inherited primary autosomal recessive microcephaly (MCPH). In addition to HeLa cells, in which centrosome number and spindle positioning can be well monitored, we analysed retinal epithelial cells (RPE-1), as well as brain-derived microglial (CHME-5) and neural progenitor (ReN) cells, using immunofluorescence. We established that ZIKV infection leads to supernumerary foci containing centriolar proteins that in some cases drive multipolar spindle assembly, as well as spindle positioning defects in HeLa, RPE-1 and CHME-5 cells, but not in ReN cells. We uncovered similar phenotypes in HeLa cells upon infection with dengue virus (DENV-2), another flavivirus that does not target brain cells and does not cause microcephaly. We conclude that infection with Flaviviridae can increase centrosome numbers and impair spindle positioning, thus potentially contributing to microcephaly in the case of Zika.

Axl Mediates ZIKA Virus Entry in Human Glial Cells and Modulates Innate Immune Responses

ZIKA virus (ZIKV) is an emerging pathogen responsible for neurological disorders and congenital microcephaly. However, the molecular basis for ZIKV neurotropism remains poorly understood. Here, we show that Axl is expressed in human microglia and astrocytes in the developing brain and that it mediates ZIKV infection of glial cells. Axl-mediated ZIKV entry requires the Axl ligand Gas6, which bridges ZIKV particles to glial cells. Following binding, ZIKV is internalized through clathrin-mediated endocytosis and traffics to Rab5+ endosomes to establish productive infection. During entry, the ZIKV/Gas6 complex activates Axl kinase activity, which downmodulates interferon signaling and facilitates infection. ZIKV infection of human glial cells is inhibited by MYD1, an engineered Axl decoy receptor, and by the Axl kinase inhibitor R428. Our results highlight the dual role of Axl during ZIKV infection of glial cells: promoting viral entry and modulating innate immune responses. Therefore, inhibiting Axl function may represent a potential target for future antiviral therapies.

Infection of a French Population of Aedes albopictus and of Aedes aegypti (Paea Strain) with Zika Virus Reveals Low Transmission Rates to These Vectors' Saliva

Disease caused by the Zika virus (ZIKV) is a public health emergency of international concern. Recent epidemics have emerged in different regions of the world and attest to the ability of the virus to spread wherever its vector, Aedes species mosquitoes, can be found. We have compared the transmission of ZIKV by Ae. aegypti (PAEA strain originating from Tahiti) and by a French population of Ae. albopictus to better assess their competence and the potential risk of the emergence of ZIKV in Europe. We assessed the transmission of ZIKV by Ae. albopictus in temperatures similar to those in Southern France during the summer. Our study shows that the extrinsic incubation period of Ae. aegypti for transmission was shorter than that of Ae. albopictus. Both vectors were able to transmit ZIKV from 10 to 14 days post-infection. Ae. aegypti, however, had a longer transmission period than the French population of Ae. albopictus. Although the salivary glands of both vectors are highly infected, transmission rates of ZIKV to saliva remain relatively low. These observations may suggest that the risk of emergence of ZIKV in Europe could be low.

First detection of dengue and chikungunya viruses in natural populations of Aedes aegypti in Martinique during the 2013 - 2015 concomitant outbreak

Dengue and chikungunya viruses are transmitted by Aedes mosquitoes. In Martinique, an island of the French West Indies, Aedes aegypti is the suspected vector of both arboviruses; there is no Aedes albopictus on the island. During the concomitant outbreak of 2013 - 2015, the authors collected wild A. aegypti populations, and for the first time, detected dengue and chikungunya viruses in field-collected females. This paper demonstrates the mosquito's role in transmission of both dengue and chikungunya on the island, and also highlights a tool that public health authorities can use for preventing outbreaks.

Co-Infection of Mosquitoes with Chikungunya and Dengue Viruses Reveals Modulation of the Replication of Both Viruses in Midguts and Salivary Glands of Aedes aegypti Mosquitoes

Arthropod-borne virus (arbovirus) infections cause several emerging and resurgent infectious diseases in humans and animals. Chikungunya-affected areas often overlap with dengue-endemic areas. Concurrent dengue virus (DENV) and chikungunya virus (CHIKV) infections have been detected in travelers returning from regions of endemicity. CHIKV and DENV co-infected Aedes albopictus have also been collected in the vicinity of co-infected human cases, emphasizing the need to study co-infections in mosquitoes. We thus aimed to study the pathogen-pathogen interaction involved in these co-infections in DENV/CHIKV co-infected Aedes aegypti mosquitoes. In mono-infections, we detected CHIKV antigens as early as 4 days post-virus exposure in both the midgut (MG) and salivary gland (SG), whereas we detected DENV serotype 2 (DENV-2) antigens from day 5 post-virus exposure in MG and day 10 post-virus exposure in SG. Identical infection rates were observed for singly and co-infected mosquitoes, and facilitation of the replication of both viruses at various times post-viral exposure. We observed a higher replication for DENV-2 in SG of co-infected mosquitoes. We showed that mixed CHIKV and DENV infection facilitated viral replication in Ae. aegypti. The outcome of these mixed infections must be further studied to increase our understanding of pathogen-pathogen interactions in host cells.

Dengue subgenomic flaviviral RNA disrupts immunity in mosquito salivary glands to increase virus transmission

Globally re-emerging dengue viruses are transmitted from human-to-human by Aedes mosquitoes. While viral determinants of human pathogenicity have been defined, there is a lack of knowledge of how dengue viruses influence mosquito transmission. Identification of viral determinants of transmission can help identify isolates with high epidemiological potential. Additionally, mechanistic understanding of transmission will lead to better understanding of how dengue viruses harness evolution to cycle between the two hosts. Here, we identified viral determinants of transmission and characterized mechanisms that enhance production of infectious saliva by inhibiting immunity specifically in salivary glands. Combining oral infection of Aedes aegypti mosquitoes and reverse genetics, we identified two 3’ UTR substitutions in epidemic isolates that increased subgenomic flaviviral RNA (sfRNA) quantity, infectious particles in salivary glands and infection rate of saliva, which represents a measure of transmission. We also demonstrated that various 3’UTR modifications similarly affect sfRNA quantity in both whole mosquitoes and human cells, suggesting a shared determinism of sfRNA quantity. Furthermore, higher relative quantity of sfRNA in salivary glands compared to midgut and carcass pointed to sfRNA function in salivary glands. We showed that the Toll innate immune response was preferentially inhibited in salivary glands by viruses with the 3’UTR substitutions associated to high epidemiological fitness and high sfRNA quantity, pointing to a mechanism for higher saliva infection rate. By determining that sfRNA is an immune suppressor in a tissue relevant to mosquito transmission, we propose that 3’UTR/sfRNA sequence evolution shapes dengue epidemiology not only by influencing human pathogenicity but also by increasing mosquito transmission, thereby revealing a viral determinant of epidemiological fitness that is shared between the two hosts.

Dengue is a re-emerging global disease transmitted from human-to-human by mosquitoes. While environmental and host immune factors are important, viral determinants of mosquito transmission also shape the epidemiology of dengue. Understanding how dengue viruses influence transmission will help identify isolates with high epidemic potential and untangle the evolutionary pressures at play in the dual-host cycle. Here, we identified 2 substitutions in the 3’UTR of epidemic isolates that increase transmission through immune suppression in the salivary glands. Using oral infection of Aedes aegypti mosquitoes, we reported that epidemic isolates produced more subgenomic flaviviral RNA (sfRNA) in salivary glands. SfRNA is generated from the 3’UTR sequence remaining after partial genome degradation by a host nuclease. Using reverse genetics, we identified the two 3’UTR substitutions responsible for the higher sfRNA quantity in salivary glands. We further showed that these substitutions increased dengue virus titer in salivary glands and rate of saliva infection, and suppressed the Toll immune response in salivary glands. Our study identifies the substitutions that determine virus epidemiological fitness and provides a mechanism for sfRNA-mediated enhancement of transmission. Together with previous work demonstrating that sfRNA sequence modification influences dengue virus pathogenicity in human, and that shows variation in sfRNA sequence when the viruses transition from one host to vector and vice versa, our study supports that sfRNA evolution is constrained in the two hosts.

Peridomestic Aedes malayensis and Aedes albopictus are capable vectors of arboviruses in cities

BACKGROUND

Dengue and chikungunya are global re-emerging mosquito-borne diseases. In Singapore, sustained vector control coupled with household improvements reduced domestic mosquito populations for the past 45 years, particularly the primary vector Aedes aegypti. However, while disease incidence was low for the first 30 years following vector control implementation, outbreaks have re-emerged in the past 15 years. Epidemiological observations point to the importance of peridomestic infection in areas not targeted by control programs. We investigated the role of vectors in peri-domestic areas.

METHODS

We carried out entomological surveys to identify the Aedes species present in vegetated sites in highly populated areas and determine whether mosquitoes were present in open-air areas frequented by people. We compared vector competence of Aedes albopictus and Aedes malayensis with Ae. aegypti after oral infection with sympatric dengue serotype 2 and chikungunya viruses. Mosquito saliva was tested for the presence of infectious virus particles as a surrogate for transmission following oral infection.

RESULTS

We identified Aedes albopictus and Aedes malayensis throughout Singapore and quantified their presence in forested and opened grassy areas. Both Ae. albopictus and Ae. malayensis can occupy sylvatic niches and were highly susceptible to both arboviruses. A majority of saliva of infected Ae. malayensis contained infectious particles for both viruses.

CONCLUSIONS

Our study reveals the prevalence of competent vectors in peri-domestic areas, including Ae. malayensis for which we established the vector status. Epidemics can be driven by infection foci, which are epidemiologically enhanced in the context of low herd immunity, selective pressure on arbovirus transmission and the presence of infectious asymptomatic persons, all these conditions being present in Singapore. Learning from Singapore's vector control success that reduced domestic vector populations, but has not sustainably reduced arboviral incidence, we suggest including peri-domestic vectors in the scope of vector management.

Infections and cancer: the "fifty shades of immunity" hypothesis

BACKGROUND

Since the beginning of the twentieth century, infection has emerged as a fundamental aspect of cancer causation with a growing number of pathogens recognized as oncogenic. Meanwhile, oncolytic viruses have also attracted considerable interest as possible agents of tumor destruction.

DISCUSSION

Lost in the dichotomy between oncogenic and oncolytic agents, the indirect influence of infectious organisms on carcinogenesis has been largely unexplored. We describe the various ways - from functional aspects to evolutionary considerations such as modernity mismatches - by which infectious organisms could interfere with oncogenic processes through immunity. Finally, we discuss how acknowledging these interactions might impact public health approaches and suggest new guidelines for therapeutic and preventive strategies both at individual and population levels. Infectious organisms, that are not oncogenic neither oncolytic, may play a significant role in carcinogenesis, suggesting the need to increase our knowledge about immune interactions between infections and cancer.