Zika Virus Induced Mortality and Microcephaly in Chicken Embryos

Integrative analysis of molecular pathways and morphological anomalies associated with congenital Zika syndrome

Congenital Zika syndrome (CZS) comprises a set of clinical manifestations that can be presented by neonates born to mothers infected by the Zika virus (ZIKV). CZS-associated phenotypes include neurological, skeletal, and systemic alterations and long-term developmental sequelae. One of the most frequently reported clinical conditions is microcephaly characterized by a reduction in head circumference and cognitive complications. Nevertheless, the associations among the diverse signaling pathways underlying CZS phenotypes remain to be elucidated. To shed light on CZS, we have extensively reviewed the morphological anomalies resulting from ZIKV infection, as well as genes and proteins of interest obtained from the published literature. With this list of genes or proteins, we performed computational analyses to explore the cellular processes, molecular mechanisms, and molecular pathways related to ZIKV infection. Therefore, in this review, we comprehensively describe the morphological abnormalities caused by congenital ZIKV infection and, through the analysis noted above, propose common molecular pathways altered by ZIKV that could explain both central nervous system and craniofacial skeletal alterations.

Dynamic alternations of three-dimensional chromatin architecture contribute to phenotypic characteristics of breast muscle in chicken

Breast muscle growth rate and intramuscular fat (IMF) content show apparent differences between fast-growing broilers and slow-growing indigenous chickens. However, the underlying genetic basis of these phenotypic characteristics remains elusive. In this study, we investigate the dynamic alterations of three-dimensional genome architecture and chromatin accessibility in breast muscle across four key developmental stages from embryo to starter chick in Arbor Acres (AA) broilers and Yufen (YF) indigenous chickens. The limited breed-specifically up-regulated genes (Bup-DEGs) are embedded in breed-specific A compartment, while a majority of the Bup-DEGs involving myogenesis and adipogenesis are regulated by the breed-specific TAD reprogramming. Chromatin loops allow distal accessible regions to interact with myogenic genes, and those loops share an extremely low similarity between chicken with different growth rate. Moreover, AA-specific loop interactions promote the expression of 40 Bup-DEGs, such as IGF1, which contributes to myofiber hypertrophy. YF-specific loop interactions or distal accessible regions lead to increased expression of 5 Bup-DEGs, including PIGO, PEMT, DHCR7, TMEM38B, and DHDH, which contribute to IMF deposition. These results help elucidate the regulation of breast muscle growth and IMF deposition in chickens.

The Susceptibility of Chickens to Zika Virus: A Comprehensive Study on Age-Dependent Infection Dynamics and Host Responses

Zika virus (ZIKV) remains a public health concern, with epidemics in endemic regions and sporadic outbreaks in new areas posing significant threats. Several mosquito-borne flaviviruses that can cause human illness, including West Nile, Usutu, and St. Louis encephalitis, have associations with birds. However, the susceptibility of chickens to ZIKV and their role in viral epidemiology is not currently known. We investigated the susceptibility of chickens to experimental ZIKV infection using chickens ranging from 1-day-old chicks to 6-week-old birds. ZIKV caused no clinical signs in chickens of all age groups tested. Viral RNA was detected in the blood and tissues during the first 5 days post-inoculation in 1-day and 4-day-old chicks inoculated with a high viral dose, but ZIKV was undetectable in 6-week-old birds at all timepoints. Minimal antibody responses were observed in 6-week-old birds, and while present in younger chicks, they waned by 28 days post-infection. Innate immune responses varied significantly between age groups. Robust type I interferon and inflammasome responses were measured in older chickens, while limited innate immune activation was observed in younger chicks. Signal transducer and activator of transcription 2 (STAT2) is a major driver of host restriction to ZIKV, and chicken STAT2 is distinct from human STAT2, potentially contributing to the observed resistance to ZIKV infection. The rapid clearance of the virus in older chickens coincided with an effective innate immune response, highlighting age-dependent susceptibility. Our study indicates that chickens are not susceptible to productive ZIKV infection and are unlikely to play a role in the ZIKV epidemiology.

Hepatic damage caused by flaviviruses: A systematic review

Flaviviruses infect arthropods and mammals and their pathologies are a considerable global health problem, affecting about 400 million people per year. The symptoms of these flaviviruses range from mild manifestations such as nausea, vomiting, and headache to more serious cases such as hemorrhage, meningitis, microcephaly, kidney, and liver failure. This review aims to compile the morphological changes that occur due to infections caused by dengue, yellow fever, and Zika viruses, as well as to describe possible mechanisms of action of such flaviviruses in the liver. PRISMA guidelines were used to search for studies associating flavivirus with liver disorders. Two independent reviewers selected the studies on PubMed/Medline, Web of Science, and Scopus search platforms. The SYRCLE software was used for the evaluation of the study's quality. Eighteen experimental articles were included. The experimental animals often used in experiments were monkeys (5 %), hamsters (10 %), chicken embryos (10 %), and mice (75 %). It is evident that there is a strong hepatic interaction with flaviviruses, and the main hepatic alterations found were steatosis, apoptosis, necrosis, hemorrhage, elevation of ALT and AST levels, and total bilirubin. Flavivirus infection, in general, trigger an upregulation of pro-inflammatory cytokines, leading to structural changes in mitochondria that activate cascades of cellular death and promote insulin resistance. The majority of the studies primarily focus on dengue and yellow fever viruses, while the findings related to Zika virus exposure are still relatively limited and require further investigation.

In vivo models to study neurogenesis and associated neurodevelopmental disorders-Microcephaly and autism spectrum disorder

The genesis and functioning of the central nervous system are one of the most intricate and intriguing aspects of embryogenesis. The big lacuna in the field of human CNS development is the lack of accessibility of the human brain for direct observation during embryonic and fetal development. Thus, it is imperative to establish alternative animal models to gain deep mechanistic insights into neurodevelopment, establishment of neural circuitry, and its function. Neurodevelopmental events such as neural specification, differentiation, and generation of neuronal and non-neuronal cell types have been comprehensively studied using a variety of animal models and in vitro model systems derived from human cells. The experimentations on animal models have revealed novel, mechanistic insights into neurogenesis, formation of neural networks, and function. The models, thus serve as indispensable tools to understand the molecular basis of neurodevelopmental disorders (NDDs) arising from aberrations during embryonic development. Here, we review the spectrum of in vivo models such as fruitfly, zebrafish, frog, mice, and nonhuman primates to study neurogenesis and NDDs like microcephaly and Autism Spectrum Disorder. We also discuss nonconventional models such as ascidians and the recent technological advances in the field to study neurogenesis, disease mechanisms, and pathophysiology of human NDDs. This article is categorized under: Cancer > Stem Cells and Development Congenital Diseases > Stem Cells and Development Neurological Diseases > Stem Cells and Development Congenital Diseases > Genetics/Genomics/Epigenetics.

Exploring the Expression and Function of cTyro3, a Candidate Zika Virus Receptor, in the Embryonic Chicken Brain and Inner Ear

The transmembrane protein Axl was proposed as an entry receptor for Zika virus (ZIKV) infection in vitro, but conflicting results from in vivo studies have made it difficult to establish Axl as a physiologically relevant ZIKV receptor. Both the functional redundancy of receptors and the experimental model used can lead to variable results. Therefore, it can be informative to explore alternative animal models to analyze ZIKV receptor candidates as an aid in discovering antivirals. This study used chicken embryos to examine the role of chicken Tyro3 (cTyro3), the equivalent of human Axl. Results show that endogenous cTyro3 mRNA expression overlaps with previously described hot spots of ZIKV infectivity in the brain and inner ear. We asked if ectopic expression or knockdown of cTyro3 influenced ZIKV infection in embryos. Tol2 vectors or replication-competent avian retroviruses were used in ovo to introduce full-length or truncated (presumed dominant-negative) cTyro3, respectively, into the neural tube on embryonic day two (E2). ZIKV was delivered to the brain 24 h later. cTyro3 manipulations did not alter ZIKV infection or cell death in the E5/E6 brain. Moreover, delivery of truncated cTyro3 variants to the E3 otocyst had no effect on inner ear formation on E6 or E10.

Pathophysiology and mechanisms of hearing impairment related to neonatal infection diseases

The inner ear, the organ of equilibrium and hearing, has an extraordinarily complex and intricate arrangement. It contains highly specialized structures meticulously tailored to permit auditory processing. However, hearing also relies on both peripheral and central pathways responsible for the neuronal transmission of auditory information from the cochlea to the corresponding cortical regions. Understanding the anatomy and physiology of all components forming the auditory system is key to better comprehending the pathophysiology of each disease that causes hearing impairment. In this narrative review, the authors focus on the pathophysiology as well as on cellular and molecular mechanisms that lead to hearing loss in different neonatal infectious diseases. To accomplish this objective, the morphology and function of the main structures responsible for auditory processing and the immune response leading to hearing loss were explored. Altogether, this information permits the proper understanding of each infectious disease discussed.

Molecular survey of Zika virus in the animal-human interface in traditional farming

Backyard animal husbandry is common in rural communities in developing countries and, given the conditions in which it occurs, it can increase the risk of disease transmission, such as arboviruses. To determine the presence of the Zika virus (ZIKV) and abundance of its arthropod vectors we evaluated the socioeconomic implications involved in its transmission in two highly vulnerable Mayan communities in the state of Yucatan that practice backyard farming. An analytical cross-sectional study was carried out throughout 2016 to understand socioeconomic variables and seasonal patterns in mosquito populations. We selected 20 households from each community. Social exclusion indicators were analyzed, human and domestic animals were sampled, and mosquitoes were collected and identified. Four out of eight indicators of social exclusion were higher than the reported national averages. We captured 5,825 mosquitoes from 16 species being Culex quinquefasciatus and Aedes aegypti the most abundant. The presence of chickens and human overcrowding in dwellings were the most significant factors (P = 0.026) associated with the presence of Ae. aegypti. Septic tanks (odds ratio = 6.64) and chickens (odds ratio = 27.41) in backyards were the main risk factors associated with the presence of immature states of Ae. aegypti in both communities. Molecular analysis to detect ZIKV was performed in blood samples from 416 humans, 1,068 backyard animals and 381 mosquito pools. Eighteen humans and 10 pig pools tested positive for ZIKV. Forty-three mosquito pools tested positive for flavivirus. Ten of the 43 pools of positive mosquitoes were sequenced, corresponding 3/10 to ZIKV and 1/10 to Dengue virus type 2. The findings obtained indicate the continuous circulation of Flavivirus (including ZIKV) in backyard environments in vulnerable communities, highlighting the importance of studying their transmission and maintenance in these systems, due that backyard animal husbandry is a common practice in these vulnerable communities with limited access to health services.

Molecular Mechanisms of ZIKV-Induced Teratogenesis: A Systematic Review of Studies in Animal Models

Zika virus (ZIKV) is a teratogen that causes congenital anomalies, being linked to microcephaly in children exposed during pregnancy. Animal studies have been conducted to investigate the molecular mechanisms related to ZIKV teratogenesis. Although animal models can mimic the effects of ZIKV in human embryo development, few in vivo studies have addressed molecular changes following ZIKV infection in embryos. Moreover, few literature reviews have been conducted with these studies. The aim of this systematic review is to evaluate the molecular mechanisms of ZIKV teratogenesis determined from studies in animal models. PubMed/MEDLINE, EMBASE, Web of Science, and Scopus as well as grey literature were searched for studies that evaluated molecular alterations related to ZIKV teratogenesis which occurred during embryonic development. Nine studies were included: six with mice, one with mice and guinea pigs, one with pigs and one with chickens. In general, studies presented an unclear or high risk of bias for methodological criteria. Most of studies reported embryos exposed to ZIKV presenting microcephaly, reduced cortex thickness, and growth restriction. Different techniques were used to evaluated molecular changes in the animals following ZIKV infection: RNA sequencing, RT-qPCR, and in situ hybridization. It was found that common pathways are changed in most studies, being pathways related to immune response upregulated and those involved to neurodevelopment downregulated.

Zika Virus Infection and Development of Drug Therapeutics

Zika virus (ZIKV) is an emerging flavivirus that is associated with neurological complications, such as neuroinflammatory Guillain Barré Syndrome in adults and microcephaly in newborns, and remains a potentially significant and international public health concern. The World Health Organization is urging the development of novel antiviral therapeutic strategies against ZIKV, as there are no clinically approved vaccines or drugs against this virus. Given the public health crisis that is related to ZIKV cases in the last decade, efficient strategies should be identified rapidly to combat or treat ZIKV infection. Several promising strategies have been reported through drug repurposing studies, de novo design, and the high-throughput screening of compound libraries in only a few years. This review summarizes the genome and structure of ZIKV, viral life cycle, transmission cycle, clinical manifestations, cellular and animal models, and antiviral drug developments, with the goal of increasing our understanding of ZIKV and ultimately defeating it.

Embryonic heat conditioning in chicks induces transgenerational heat/immunological resilience via methylation on regulatory elements

The question of whether behavioral traits are heritable is under debate. An obstacle in demonstrating transgenerational inheritance in mammals originates from the maternal environment's effect on offspring phenotype. Here, we used in ovo embryonic heat conditioning (EHC) of first-generation chicks, demonstrating heredity of both heat and immunological resilience, confirmed by a reduced fibril response in their untreated offspring to either heat or LPS challenge. Concordantly, transcriptome analysis confirmed that EHC induces changes in gene expression in the anterior preoptic hypothalamus (APH) that contribute to these phenotypes in the offspring. To study the association between epigenetic mechanisms and trait heritability, DNA-methylation patterns in the APH of offspring of control versus EHC fathers were evaluated. Genome-wide analysis revealed thousands of differentially methylated sites (DMSs), which were highly enriched in enhancers and CCCTC-binding factor (CTCF) sites. Overlap analysis revealed 110 differentially expressed genes that were associated with altered methylation, predominantly on enhancers. Gene-ontology analysis shows pathways associated with immune response, chaperone-mediated protein folding, and stress response. For the proof of concept, we focused on HSP25 and SOCS3, modulators of heat and immune responses, respectively. Chromosome conformational capture (3C) assay identified interactions between their promoters and methylated enhancers, with the strongest frequency on CTCF binding sites. Furthermore, gene expression corresponded with the differential methylation patterns, and presented increased CTCF binding in both hyper- and hypomethylated DMSs. Collectively, we demonstrate that EHC induces transgenerational thermal and immunological resilience traits. We propose that one of the mechanisms underlying inheritance depends on three-dimensional (3D) chromatin reorganization.

Zika Virus and Neuropathogenesis: The Unanswered Question of Which Strain Is More Prone to Causing Microcephaly and Other Neurological Defects

Despite being perceived to be a relatively innocuous pathogen during its circulation in Africa in the 20th century, consequent outbreaks in French Polynesia and Latin America revealed the Zika virus (ZIKV) to be capable of causing severe neurological defects. Foetuses infected with the virus during pregnancy developed a range of pathologies including microcephaly, cerebral calcifications and macular scarring. These are now collectively known as Congenital Zika syndrome (CZS). It has been established that the neuropathogenesis of ZIKV results from infection of neural progenitor cells in the developing cerebral cortex. Following this, two main hypotheses have emerged: the virus causes either apoptosis or premature differentiation of neural progenitor cells, reducing the final number of mature neurons in the cerebral cortex. This review describes the cellular processes which could potentially cause virus induced apoptosis or premature differentiation, leading to speculation that a combination of the two may be responsible for the pathologies associated with ZIKV. The review also discusses which specific lineages of the ZIKV can employ these mechanisms. It has been unclear in the past whether the virus evolved its neurotropic capability following circulation in Africa, or if the virus has always caused microcephaly but public health surveillance in Africa had failed to detect it. Understanding the true neuropathogenesis of ZIKV is key to being prepared for further outbreaks in the future, and it will also provide insight into how neurotropic viruses can cause profound and life-long neurological defects.

An update on preclinical pregnancy models of Zika virus infection for drug and vaccine discovery

INTRODUCTION

Congenital Zika syndrome is caused by Zika virus (ZIKV) infection during pregnancy and can culminate in structural and neurological defects in the fetus, including a spectrum of symptoms such as brain calcifications, hydrocephalus, holoprosencephaly, lissencephaly, ventriculomegaly, and microcephaly. Using animal models to study ZIKV infection during pregnancy represents a critical tool for understanding ZIKV pathophysiology, drug testing, vaccine development, and prevention of vertical transmission.

AREAS COVERED

In this review, the authors cover state-of-the-art preclinical pregnancy models of ZIKV infection for drug discovery and vaccine development to prevent vertical transmission.

EXPERT OPINION

The discovery of drugs against ZIKV infection represents an urgent necessity, and until now, no effective drug that can prevent the effects of vertical transmission has been tested in humans. Even after six years of the ZIKV outbreak in Brazil, no drugs or vaccines have been approved for use in humans. In part, this failure could be related to the lack of translatability from available preclinical models to humans.

From the Farm to the Lab: How Chicken Embryos Contribute to the Field of Teratology

Congenital anomalies and its causes, particularly, by external factors are the aim of the field called teratology. The external factors studied by teratology are known as teratogens and can be biological or environmental factors for example, chemicals, medications, recreational drugs, environmental pollutants, physical agents (e.g., X-rays and maternal hyperthermia) and maternal metabolic conditions. Proving the teratogenicity of a factor is a difficult task requiring epidemiology studies as well as experimental teratology evidence from the use of animal models, one of which is the chicken embryo. This model in particular has the advantage of being able to follow development live and in vivo, with rapid development hatching around 21 days, is cheap and easy to manipulate and to observe development. All this allows the chicken embryo to be used in drug screening studies, teratogenic evaluation and studies of mechanisms of teratogenicity. The chicken embryo shares morphological, biochemical and genetic similarities with humans as well as mammalian species, making them ideal to ascertain the actions of teratogens, as well as screen drugs to test for their safety. Pre-clinical trials for new drugs are carried out in rodents and rabbits, however, chicken embryos have been used to screen new compounds or analogs of thalidomide as well as to investigate how some drugs can lead to congenital malformations. Indeed, the chicken embryo has proved valuable in understanding how many congenital anomalies, seen in humans, arise following teratogen exposure. The aim of this review is to highlight the role of the chicken embryo as an experimental model for studies in teratology, exploring its use in drug screening studies, phenotypic evaluation and studies of teratogenic mechanisms of action. Here, we discuss many known teratogens, that have been evaluated using the chicken embryo model including some medicines, such as, thalidomide, valproic acid; recreational drugs including alcohol; environmental influences, such as viruses, specifically ZIKV, which is a newly discovered human teratogen. In addition, we discuss how the chicken embryo has provided insight on the mechanisms of teratogenesis of many compounds and also how this impact on drug safety.

Chemerin impairs food intake and body weight in chicken: Focus on hypothalamic neuropeptides gene expression and AMPK signaling pathway

Unlike mammals, the role of adipokines and more particularly of chemerin in the regulation of food intake is totally unknown in avian species. Here we investigated the effect of chemerin on the food and water consumption and on the body weight in chicken. We studied the effects on the plasma glucose and insulin concentrations and the hypothalamic neuropeptides and AMPK signaling pathway. Female broiler chickens were intraperitoneally injected, daily for 13 days with either vehicle (saline; n = 25) or chemerin (8 μg/kg; n = 25 and 16 μg/kg; n = 25). Food and water intakes were recorded 24 h after each administration. Overnight fasted animals were sacrificed at day 13 (D13), 24 h after the last injection and hypothalamus and left cerebral hemispheres were collected. Chemerin and its receptors protein levels were determined by western-blot. Gene expression of neuropeptide Y (Npy), agouti-related peptide (Agrp), corticotrophin releasing hormone (Crh), pro-opiomelanocortin (Pomc), cocaine and amphetamine-regulated transcript (Cart) and Taste 1 Receptor Member 1 (Tas1r1) were evaluated by RT-qPCR. In chicken, we found that the protein amount of chemerin, CCRL2 and GPR1 was similar in left cerebral hemisphere and hypothalamus whereas CMKLR1 was higher in hypothalamus. Chemerin administration (8 and 16 μg/kg) decreased both food intake and body weight compared to vehicle without affecting water intake and the size or volume of different brain subdivisions as determined by magnetic resonance imaging. It also increased plasma insulin levels whereas glucose levels were decreased. These data were associated with an increase in Npy and Agrp expressions and a decrease in Crh, Tas1r1 mRNA expression within the hypothalamus. Furthermore, chemerin decreased hypothalamic CMKLR1 protein expression and AMPK activation. Taken together, these results support that chemerin could be a peripheral appetite-regulating signal through modulation of hypothalamic peptides expression in chicken.

Cas9-expressing chickens and pigs as resources for genome editing in livestock

Genetically modified animals continue to provide important insights into the molecular basis of health and disease. Research has focused mostly on genetically modified mice, although other species like pigs resemble the human physiology more closely. In addition, cross-species comparisons with phylogenetically distant species such as chickens provide powerful insights into fundamental biological and biomedical processes. One of the most versatile genetic methods applicable across species is CRISPR-Cas9. Here, we report the generation of transgenic chickens and pigs that constitutively express Cas9 in all organs. These animals are healthy and fertile. Functionality of Cas9 was confirmed in both species for a number of different target genes, for a variety of cell types and in vivo by targeted gene disruption in lymphocytes and the developing brain, and by precise excision of a 12.7-kb DNA fragment in the heart. The Cas9 transgenic animals will provide a powerful resource for in vivo genome editing for both agricultural and translational biomedical research, and will facilitate reverse genetics as well as cross-species comparisons.

A Review on the Current Knowledge on ZIKV Infection and the Interest of Organoids and Nanotechnology on Development of Effective Therapies against Zika Infection

Zika virus (ZIKV) acquired a special relevance due to the pandemic that occurred in the Americas in 2015, when an important number of fetal microcephaly cases occurred. Since then, numerous studies have tried to elucidate the pathogenic mechanisms and the potential therapeutic approaches to combat the virus. Cellular and animal models have proved to be a basic resource for this research, with the more recent addition of organoids as a more realistic and physiological 3D culture for the study of ZIKV. Nanotechnology can also offer a promising therapeutic tool, as the nanoparticles developed by this field can penetrate cells and deliver a wide array of drugs in a very specific and controlled way inside the cells. These two state-of-the-art scientific tools clearly provide a very relevant resource for the study of ZIKV, and will help researchers find an effective treatment or vaccine against the virus.

Animal models of congenital zika syndrome provide mechanistic insight into viral pathogenesis during pregnancy

In utero Zika virus (ZIKV; family Flaviviridae) infection causes a distinct pattern of birth defects and disabilities in the developing fetus and neonate that has been termed congenital zika syndrome (CZS). Over 8,000 children were affected by the 2016 to 2017 ZIKV outbreak in the Americas, many of whom developed CZS as a result of in utero exposure. To date, there is no consensus about how ZIKV causes CZS; animal models, however, are providing mechanistic insights. Using nonhuman primates, immunocompromised mice, immunocompetent mice, and other animal models (e.g., pigs, sheep, guinea pigs, and hamsters), studies are showing that maternal immunological responses, placental infection and inflammation, as well as viral genetic factors play significant roles in predicting the downstream consequences of in utero ZIKV infection on the development of CZS in offspring. There are thousands of children suffering from adverse consequences of CZS. Therefore, the animal models developed to study ZIKV-induced adverse outcomes in offspring could provide mechanistic insights into how other viruses, including influenza and hepatitis C viruses, impact placental viability and fetal growth to cause long-term adverse outcomes in an effort to identify therapeutic treatments.

Zika virus-induced brain malformations in chicken embryos

BACKGROUND

Zika virus (ZIKV) was confirmed to be related to microcephaly in 2016. However, there is still a need for understanding the embryonic morphological changes induced by ZIKV and when they occur. Here, chicken embryos were chosen as experimental model of ZIKV to evaluate virus-associated morphological alterations that might take place during embryonic development.

METHODS

A screening with different viral doses was conducted in embryos at HH Stage 10-12 (E1.5) as well as a follow up of the first 5 days postinfection (dpi) was performed to observe the main morphologic changes post ZIKV infection.

RESULTS

ZIKV exposed embryos presented a higher prevalence of mortality and defects such as brain malformation when compared to controls. Moreover, we observed that the phenotypes become more evident at 4dpi, when the viral load quantification reaches a peak.

CONCLUSIONS

We found that ZIKV exposed embryos presented a high prevalence of mortality and central nervous system (CNS) abnormalities in a dose-dependent manner. The phenotype was more evident 4 days postinfection, when the viral load quantification reached a peak.

Embryonic Heat Conditioning Induces TET-Dependent Cross-Tolerance to Hypothalamic Inflammation Later in Life

Early life encounters with stress can lead to long-lasting beneficial alterations in the response to various stressors, known as cross-tolerance. Embryonic heat conditioning (EHC) of chicks was previously shown to mediate resilience to heat stress later in life. Here we demonstrate that EHC can induce cross-tolerance with the immune system, attenuating hypothalamic inflammation. Inflammation in EHC chicks was manifested, following lipopolysaccharide (LPS) challenge on day 10 post-hatch, by reduced febrile response and reduced expression of LITAF and NFκB compared to controls, as well as nuclear localization and activation of NFκB in the hypothalamus. Since the cross-tolerance effect was long-lasting, we assumed that epigenetic mechanisms are involved. We focused on the role of ten-eleven translocation (TET) family enzymes, which are the mediators of active CpG demethylation. Here, TET transcription during early life stress was found to be necessary for stress resilience later in life. The expression of the TET family enzymes in the midbrain during conditioning increased in parallel to an elevation in concentration of their cofactor α-ketoglutarate. In-ovo inhibition of TET activity during EHC, by the α-ketoglutarate inhibitor bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl) ethyl sulfide (BPTES), resulted in reduced total and locus specific CpG demethylation in 10-day-old chicks and reversed both thermal and inflammatory resilience. In addition, EHC attenuated the elevation in expression of the stress markers HSP70, CRHR1, and CRHR2, during heat challenge on day 10 post-hatch. This reduction in expression was reversed by BPTES. Similarly, the EHC-dependent reduction of inflammatory gene expression during LPS challenge was eliminated in BPTES-treated chicks. Thus, TET family enzymes and CpG demethylation are essential for the embryonic induction of stress cross-tolerance in the hypothalamus.

Cross-tolerance: embryonic heat conditioning induces inflammatory resilience by affecting different layers of epigenetic mechanisms regulating IL6 expression later in life

A stressor can induce resilience in another, different stressor, a phenomenon known as cross-tolerance. To learn if cross-tolerance is governed by epigenetic regulation, we used embryonic heat conditioning (EHC) in chicks, during the development of the hypothalamus, to increase the immunization response. Indeed, EHC induced a lifelong systemic antibody response to immunization, in addition to reduced hypothalamic IL6 inflammatory expression following LPS challenge. Since the outcome of EHC was long-term cross-tolerance with the immune system, we studied possible epigenetic mechanisms. We first analysed the methylation and hydroxymethylation patterns of IL6. We found reduced hydroxymethylation on IL6 intron 1 in the EHC group, a segment enriched with CpGs and NFkB-binding sites. Luciferase assay in cell lines expressing NFkB showed that IL6 intron 1 is indeed an enhancer. ChiP in the same segment against NFkB in the hypothalamus presented reduced binding to IL6 intron 1 in the EHC group, before and during LPS challenge. In parallel, EHC chicks' IL6 intron 1 presented increased H3K27me3, a repressive translational modification mediated by EZH2. This histone modification occurred during embryonic conditioning and persisted later in life. Moreover, we showed reduced expression of miR-26a, which inhibits EZH2 transcription, during conditioning along with increased EZH2 expression. We demonstrate that stress cross-tolerance, which was indicated by EHC-induced inflammatory resilience and displayed by attenuated inflammatory expression of IL6, is regulated by different epigenetic layers.

Zika virus NS1 affects the junctional integrity of human brain microvascular endothelial cells

Zika virus (ZIKV) infection leads to microcephaly in newborns. Flaviviruses are known to secrete NS1 protein extracellularly and its concentration in serum directly co-relate to disease severity. The presence of ZIKV-NS1 near the brain microvascular endothelial cells (BMVECs) affects blood-brain-barrier, which is composed of tight junctions (TJs) and adherens junctions (AJs). Viruses utilize different strategies to circumvent this barrier to enter in brain. The present study demonstrated the mechanism of junctional integrity disruption in BMVECs by ZIKV-NS1 protein exposure. The Transendothelial Electrical Resistance and sodium fluorescein migration assays revealed the endothelial barrier disruption in BMVECs exposed to ZIKV-NS1 at different time (12hr and 24hr) and doses (500 ng/mL, 1000 ng/mL and 1500 ng/mL). The exposure of ZIKV-NS1 on BMVECs led to the phosphorylation of AJs and suppression of TJs through secreted ZIKV-NS1 in a bystander fashion. The activation of NADPH dependent reactive oxygen species activity and redox sensitive tyrosine kinase further increased the phosphorylation of AJs. The reduced expression of the phosphatase led to the increased phosphorylation of the AJs. The treatment with Diphenyleneiodonium chloride rescued the phosphatase and TJs expression and suppressed the expression of kinase and AJs in BMVECs exposed to ZIKV-NS1.

Usutu Virus Infection of Embryonated Chicken Eggs and a Chicken Embryo-Derived Primary Cell Line

Usutu virus (USUV) is a mosquito-borne flavivirus, closely related to the West Nile virus (WNV). Similar to WNV, USUV may cause infections in humans, with occasional, but sometimes severe, neurological complications. Further, USUV can be highly pathogenic in wild and captive birds and its circulation in Europe has given rise to substantial avian death. Adequate study models of this virus are still lacking but are critically needed to understand its pathogenesis and virulence spectrum. The chicken embryo is a low-cost, easy-to-manipulate and ethically acceptable model that closely reflects mammalian fetal development and allows immune response investigations, drug screening, and high-throughput virus production for vaccine development. While former studies suggested that this model was refractory to USUV infection, we unexpectedly found that high doses of four phylogenetically distinct USUV strains caused embryonic lethality. By employing immunohistochemistry and quantitative reverse transcriptase-polymerase chain reaction, we demonstrated that USUV was widely distributed in embryonic tissues, including the brain, retina, and feather follicles. We then successfully developed a primary cell line from the chorioallantoic membrane that was permissive to the virus without the need for viral adaptation. We believe the future use of these models would foster a significant understanding of USUV-induced neuropathogenesis and immune response and allow the future development of drugs and vaccines against USUV.

Zika virus can directly infect and damage the auditory and vestibular components of the embryonic chicken inner ear

BACKGROUND

Sensorineural hearing loss is an understudied consequence of congenital Zika syndrome, and balance disorders are essentially unreported to date. Also lacking is information about the susceptibility and the pathogenesis of the developing inner ear following Zika virus (ZIKV) exposure. To address this, ZIKV was delivered directly into the otic cup/otocyst of chicken embryos and infection of inner ear tissues was evaluated using immunohistochemistry.

RESULTS

After injections on embryonic days 2 to 5, ZIKV infection was observed in 90% of the samples harvested 2 to 8 days later; however, the degree of infection was highly variable across individuals. ZIKV was detected in all regions of the inner ear, associated ganglia, and in the surrounding periotic mesenchyme. Detection of virus peaked earlier in the ganglion and vestibular compartments, and later in the cochlea. ZIKV infection increased cell death robustly in the auditory ganglion, and modestly in the auditory sensory organ. Macrophage accumulation was found to overlap with dense viral infection in some tissues. Additionally, dysmorphogenesis of the semicircular canals and ganglion was observed for a subset of injection conditions.

CONCLUSIONS

This article presents evidence of direct ZIKV infection of developing inner ear epithelium and shows previously unknown inner ear dysmorphogenesis phenotypes.

Susceptibility of Chicken Embryos, Sheep, Cattle, Pigs, and Chickens to Zika Virus Infection

The susceptibility of sheep, cattle, pigs, chickens and chicken embryos to Zika virus infection was evaluated by experimental inoculation with Zika virus Thailand strain isolated from a Canadian traveler in 2013. The inoculated animals did not develop any clinical signs of disease nor evidence of Zika virus replication in peripheral blood, cerebrospinal fluid and tissues including brain and spinal cord assessed by real-time RT-PCR. Sera were also negative for Zika virus antibodies by Zika virus neutralization assays as well as Zika virus immunoperoxidase staining of Zika infected Vero cells. Chicken embryos were inoculated by different routes including yolk sac (4 day old embryos), chorioallantoic membrane (8 day old embryos), amniotic fluid (8 day old embryos) and intravenous routes (12 day old embryos). Virus replication in chicken embryos was observed in the brain and body tissues following intravenous (IV), yolk sac (YS), chorioallantoic membrane (CAM), and amniotic fluid (AF) inoculation routes. The highest mortality was observed in embryos inoculated via yolk sac. The dead embryos showed diffuse muscular hemorrhages. The yolk sac inoculated chicken embryos showed delayed hatching and displayed neurological signs immediately after hatching. These studies demonstrate that 8 week old sheep, 6 month old cattle, 4 week old pigs, and 4 week old chickens are not susceptible to Zika virus infection when inoculated experimentally and therefore unlikely to pose a risk as Zika virus reservoirs. However, chicken embryos are highly susceptible to Zika virus resulting in clinical disease of chicks after hatching. This study demonstrates that Zika virus has a tropism for embryonic tissue and that chicken embryos can be used as a model to study Zika virus replication and pathogenesis.

Zika Vaccine Development: Current Status

Zika virus outbreaks have been explosive and unpredictable and have led to significant adverse health effects-as well as considerable public anxiety. Significant scientific work has resulted in multiple candidate vaccines that are now undergoing further clinical development, with several vaccines now in phase 2 clinical trials. In this review, we survey current vaccine efforts, preclinical and clinical results, and ethical and other concerns that directly bear on vaccine development. It is clear that the world needs safe and effective vaccines to protect against Zika virus infection. Whether such vaccines can be developed through to licensure and public availability absent significant financial investment by countries, and other barriers discussed within this article, remains uncertain.

Zika virus and microcephaly in Southeast Asia: A cause for concern?

Zika virus (ZIKV), a mosquito transmitted virus in the family Flaviviridae, genus Flavivirus, recently emerged to cause infections in more than 70 countries and territories around the world. While human infection is normally asymptomatic, it can also result in a mild febrile disease similar to dengue fever. However, when a pregnant woman is infected, ZIKV can cause fetal abnormalities including microcephaly. Evidence has suggested that ZIKV has circulated in Southeast Asia for more than a decade and yet cases of ZIKV associated microcephaly remain sparsely documented. This review seeks to collate the information currently existing on ZIKV associated microcephaly in Southeast Asia, and assess the potential future risk posed by this virus.

Zika Virus Can Strongly Infect and Disrupt Secondary Organizers in the Ventricular Zone of the Embryonic Chicken Brain

Zika virus (ZIKV) is associated with severe neurodevelopmental impairments in human fetuses, including microencephaly. Previous reports examining neural progenitor tropism of ZIKV in organoid and animal models did not address whether the virus infects all neural progenitors uniformly. To explore this, ZIKV was injected into the neural tube of 2-day-old chicken embryos, resulting in nonuniform periventricular infection 3 days later. Recurrent foci of intense infection were present at specific signaling centers that influence neuroepithelial patterning at a distance through secretion of morphogens. ZIKV infection reduced transcript levels for 3 morphogens, SHH, BMP7, and FGF8 expressed at the midbrain basal plate, hypothalamic floor plate, and isthmus, respectively. Levels of Patched1, a SHH-pathway downstream gene, were also reduced, and a SHH-dependent cell population in the ventral midbrain was shifted in position. Thus, the diminishment of signaling centers through ZIKV-mediated apoptosis may yield broader, non-cell-autonomous changes in brain patterning.

Role of adherens junctions and apical-basal polarity of neural stem/progenitor cells in the pathogenesis of neurodevelopmental disorders: a novel perspective on congenital Zika syndrome

Radial glial cells (RGCs) are the neural stem/progenitor cells (NSPCs) that give rise to most of neurons and glial cells that constitute the adult central nervous system. A hallmark of RGCs is their polarization along the apical-basal axis. They extend a long basal process that contacts the pial surface and a short apical process to the ventricular surface. Adherens junctions (AJs) are organized as belt-like structures at the most-apical lateral plasma membrane of the apical processes. These junctional complexes anchor RGCs to each other and allow the recruitment of cytoplasmic proteins that act as apical-basal determinants. It has been proposed that disruption of AJs underlies the onset of different neurodevelopmental disorders. In fact, studies performed in different animal models indicate that loss of function of AJs-related proteins in NSPCs can disrupt cell polarity, imbalance proliferation and/or differentiation rates and increase cell death, which, in turn, lead to disruption of the cytoarchitecture of the ventricular zone, protrusion of non-polarized cells into the ventricles, cortical thinning, and ventriculomegaly/hydrocephalus, among other neuropathological findings. Recent Zika virus (ZIKV) outbreaks and the high comorbidity of ZIKV infection with congenital neurodevelopmental defects have led to the World Health Organization to declare a public emergency of international concern. Thus, noteworthy advances have been made in clinical and experimental ZIKV research. This review summarizes the current knowledge regarding the function of AJs in normal and pathological corticogenesis and focuses on the neuropathological and cellular mechanisms involved in congenital ZIKV syndrome, highlighting the potential role of cell-to-cell junctions between NSPCs in the etiopathogenesis of such syndrome.

In vitro and in silico Models to Study Mosquito-Borne Flavivirus Neuropathogenesis, Prevention, and Treatment

Mosquito-borne flaviviruses can cause disease in the nervous system, resulting in a significant burden of morbidity and mortality. Disease models are necessary to understand neuropathogenesis and identify potential therapeutics and vaccines. Non-human primates have been used extensively but present major challenges. Advances have also been made toward the development of humanized mouse models, but these models still do not fully represent human pathophysiology. Recent developments in stem cell technology and cell culture techniques have allowed the development of more physiologically relevant human cell-based models. In silico modeling has also allowed researchers to identify and predict transmission patterns and discover potential vaccine and therapeutic candidates. This review summarizes the research on in vitro and in silico models used to study three mosquito-borne flaviviruses that cause neurological disease in humans: West Nile, Dengue, and Zika. We also propose a roadmap for 21st century research on mosquito-borne flavivirus neuropathogenesis, prevention, and treatment.

Pathophysiology and Mechanisms of Zika Virus Infection in the Nervous System

In 2015, public awareness of Zika virus (ZIKV) rose in response to alarming statistics of infants with microcephaly being born to women who were infected with the virus during pregnancy, triggering global concern over these potentially devastating consequences. Although we have discovered a great deal about the genome and pathogenesis of this reemergent flavivirus since this recent outbreak, we still have much more to learn, including the nature of the virus-host interactions and mechanisms that determine its tropism and pathogenicity in the nervous system, which are in turn shaped by the continual evolution of the virus. Inevitably, we will find out more about the potential long-term effects of ZIKV exposure on the nervous system from ongoing longitudinal studies. Integrating clinical and epidemiological data with a wider range of animal and human cell culture models will be critical to understanding the pathogenetic mechanisms and developing more specific antiviral compounds and vaccines.

Update on the Animal Models and Underlying Mechanisms for ZIKV-Induced Microcephaly

The circulation of Zika virus (ZIKV) in nearly 80 countries and territories poses a significant global threat to public health. ZIKV is causally linked to severe developmental defects in the brain, recognized as congenital Zika syndrome (CZS), which includes microcephaly and other serious congenital neurological complications. Since the World Health Organization declared the ZIKV outbreak a public health emergency of international concern, remarkable progress has been made in the generation of different ZIKV infection animal models to gain insight into cellular targets and pathogenesis and to explore the associated underlying mechanisms. Here we focus on summarizing our current understanding of the effects of ZIKV on mammalian brain development in different developmental stages and discuss the potential underlying mechanisms of ZIKV-induced CZS, as well as future perspectives.

Zika Virus Induced More Severe Inflammatory Response Than Dengue Virus in Chicken Embryonic Livers

Dengue (DENV) and Zika virus (ZIKV) are important flaviviruses in tropical and subtropical regions, causing severe Dengue Hemorrhagic Fever (DHF)/Dengue Shock Syndrome (DSS) and microcephaly, respectively. The infection of both viruses during pregnancy were reported with adverse fetal outcomes. To investigate the effects of ZIKV and DENV infections on fetal development, we established an infection model in chicken embryos. Compared with DENV-2, the infection of ZIKV significantly retarded the development of chicken embryos. High viral loads of both DENV-2 and ZIKV was detected in brain, eye and heart 7 and 11 days post-infection, respectively. Interestingly, only ZIKV but not DENV-2 was detected in the liver. Even both of them induced apparent liver inflammation, ZIKV infection showed a more severe inflammatory response than DENV-2 infection based on the inflammation scores and the gene expression levels of IL-1β, TNF, IL-6, and TGFβ-2 in liver. Our results demonstrated that ZIKV induced more severe inflammatory response in chicken embryo liver compared to DENV-2, which might partially attribute to viral replication in liver cells. Clinicians should be aware of the potential liver injury associated with ZIKV infection in patients, especially in perinatal fetuses.

Zika virus: Molecular responses and tissue tropism in the mammalian host

Zika virus (ZIKV) outbreaks have raised alarm because of reports of congenital Zika virus syndrome in infants. The virus is also known to cause the debilitating Guillain-Barré syndrome in adults. As a result, extensive research has been carried out on the virus over the past few years. To study the molecular responses of viral infectivity in mammals, in vitro two-dimensional and three-dimensional cellular models have been employed. The in vivo models of mouse, pig, chicken, and nonhuman primates are primarily used to investigate the teratogenicity of the virus, to study effects of the virus on specific tissues, and to study the systemic effects of a proposed antiviral agent. The virus exhibits wide tissue tropism in the mammalian host. The major host tissues of viral persistence and propagation are neural tissue, ocular tissue, testicular tissue and placental tissue. An understanding of the function of viral components, viral replication cycle, and the molecular responses elicited in the host tissues is imperative for designing antiviral treatment strategies and for development of vaccines. This review provides an update on ZIKV research models and mammalian host responses with respect to ZIKV tissue infection.

Developing animal models of Zika virus infection for novel drug discovery

INTRODUCTION

Just before the Brazilian outbreak, Zika virus was related to a mild infection, causing fever and skin rash. Congenital Zika Syndrome was first described in Brazil, causing microcephaly and malformations in newborns. Three years after the outbreak, the mechanisms of Zika pathogenesis are still not completely elucidated. Moreover, as of today, there is still no approved vaccine that can be administered to the susceptible population. Considering the unmet clinical need, animal models represent an unprecedented opportunity to study Zika pathophysiology and test drugs for the treatment and prevention of vertical transmission. Areas covered: The authors explore the current knowledge about Zika through animal models and advancements in drug discovery by highlighting drugs with the greatest potential to treat ZIKV infection and block vertical transmission. Expert opinion: Some drugs used to treat other infections have been repurposed to treat Zika infection, reducing the cost and time for clinical application. One promising example is Sofosbuvir, which protected mice models against Zika pathogenesis by preventing vertical transmission. Importantly, there is a lack on exploration on the long-term effects of Zika Congenital Syndrome, as well as the possible ways to treat its sequelae.

Small-Animal Models of Zika Virus

Zika virus (ZIKV) infection can result in serious consequences, including severe congenital manifestations, persistent infection in the testes, and neurologic sequelae. After a pandemic emergence, the virus has spread to much of North and South America and has been introduced to many countries outside of ZIKV-endemic areas as infected travelers return to their home countries. Rodent models have been important in gaining a better understanding of the wide range of disease etiologies associated with ZIKV infection and for the initial phase of developing countermeasures to prevent or treat viral infections. We discuss herein the advantages and disadvantages of small-animal models that have been developed to replicate various aspects of disease associated with ZIKV infection.

Proteolytic cleavage of host proteins by the Group IV viral proteases of Venezuelan equine encephalitis virus and Zika virus

The alphaviral nonstructural protein 2 (nsP2) cysteine proteases (EC 3.4.22.-) are essential for the proteolytic processing of the nonstructural (ns) polyprotein and are validated drug targets. A common secondary role of these proteases is to antagonize the effects of interferon (IFN). After delineating the cleavage site motif of the Venezuelan equine encephalitis virus (VEEV) nsP2 cysteine protease, we searched the human genome to identify host protein substrates. Here we identify a new host substrate of the VEEV nsP2 protease, human TRIM14, a component of the mitochondrial antiviral-signaling protein (MAVS) signalosome. Short stretches of homologous host-pathogen protein sequences (SSHHPS) are present in the nonstructural polyprotein and TRIM14. A 25-residue cyan-yellow fluorescent protein TRIM14 substrate was cleaved in vitro by the VEEV nsP2 protease and the cleavage site was confirmed by tandem mass spectrometry. A TRIM14 cleavage product also was found in VEEV-infected cell lysates. At least ten other Group IV (+)ssRNA viral proteases have been shown to cleave host proteins involved in generating the innate immune responses against viruses, suggesting that the integration of these short host protein sequences into the viral protease cleavage sites may represent an embedded mechanism of IFN antagonism. This interference mechanism shows several parallels with those of CRISPR/Cas9 and RNAi/RISC, but with a protease recognizing a protein sequence common to both the host and pathogen. The short host sequences embedded within the viral genome appear to be analogous to the short phage sequences found in a host's CRISPR spacer sequences. To test this algorithm, we applied it to another Group IV virus, Zika virus (ZIKV), and identified cleavage sites within human SFRP1 (secreted frizzled related protein 1), a retinal G_s alpha subunit, NT5M, and Forkhead box protein G1 (FOXG1) in vitro. Proteolytic cleavage of these proteins suggests a possible link between the protease and the virus-induced phenotype of ZIKV. The algorithm may have value for selecting cell lines and animal models that recapitulate virus-induced phenotypes, predicting host-range and susceptibility, selecting oncolytic viruses, identifying biomarkers, and de-risking live virus vaccines. Inhibitors of the proteases that utilize this mechanism may both inhibit viral replication and alleviate suppression of the innate immune responses.

Demonstrating vaccine effectiveness during a waning epidemic: A WHO/NIH meeting report on approaches to development and licensure of Zika vaccine candidates

Since its peak in early 2016, the incidence of Zika virus (ZIKV) cases has declined to such low levels that Phase 3 field efficacy trials may be infeasible. While great progress was made to rapidly advance several vaccine candidates into Phase 1 and 2 clinical trials, in the absence of sustained viral transmission it may be difficult to evaluate the effectiveness of ZIKV vaccine candidates by conducting traditional clinical disease endpoint efficacy studies. However, ZIKV is still circulating at low levels in some areas and is likely to re-emerge in naïve populations or in sites of prior epidemics once population immunity wanes. Therefore, the public health need for a ZIKV vaccine remains. To facilitate continued ZIKV vaccine development efforts, the World Health Organization's Initiative for Vaccine Research and the National Institutes of Health's National Institute of Allergy and Infectious Diseases co-hosted a meeting of experts in March 2018 to identify strategies to demonstrate vaccine effectiveness in view of waning ZIKV disease incidence. This paper outlines points for consideration for developers, regulators, and other stakeholders working towards a licensed ZIKV vaccine. These deliberations may also be applicable to development of vaccines for other emerging infections where the size, unpredictability, and ephemeral nature of outbreaks makes clinical disease endpoint efficacy trials to demonstrate vaccine effectiveness infeasible.

A 'Furry-Tale' of Zika Virus Infection: What Have We Learned from Animal Models?

The worldwide attention that the Zika virus (ZIKV) attracted, following its declaration as a Public Health Emergency of International concern by WHO in 2016, has led to a large collective effort by the international scientific community to understand its biology. Despite the mild symptoms caused by ZIKV in most infected people, the virus displays a number of worrying features, such as its ability to cause transplacental infection, fetal abnormalities and vector independent transmission through body fluids. In addition, the virus has been associated with the induction of Guillain-Barre syndrome in a number of infected individuals. With travelling, the virus has spread outside the original ZIKV endemic areas making it imperative to find ways to control it. Thus far, the large number of animal models developed to study ZIKV pathogenesis have proven to be valuable tools in understanding how the virus replicates and manifests itself in the host, its tissue tropism and the type of immune responses it induces. Still, vital questions, such as the molecular mechanisms of ZIKV persistence and the long-term consequences of ZIKV infection in the developing brain, remain unanswered. Here, we reviewed and discussed the major and most recent findings coming from animal studies and their implications for a ZIKV vaccine design.

Animal Models of Zika Virus Infection during Pregnancy

Zika virus (ZIKV) emerged suddenly in the Americas in 2015 and was associated with a widespread outbreak of microcephaly and other severe congenital abnormalities in infants born to mothers infected during pregnancy. Vertical transmission of ZIKV in humans was confirmed when viral RNA was detected in fetal and placental tissues, and this outcome has been recapitulated experimentally in animals. Unlike other flaviviruses, ZIKV is both arthropod- and sexually-transmitted, and has a broad tissue tropism in humans, including multiple tissues of the reproductive tract. The threats posed by ZIKV have prompted the development of multiple in vivo models to better understand the pathogenesis of ZIKV, particularly during pregnancy. Here, we review the progress on animal models of ZIKV infection during pregnancy. These studies have generated a foundation of insights into the biology of ZIKV, and provide a means for evaluating vaccines and therapeutics.

Estimating the effects of variation in viremia on mosquito susceptibility, infectiousness, and R0 of Zika in Aedes aegypti

Zika virus (ZIKV) is an arbovirus primarily transmitted by Aedes mosquitoes. Like most viral infections, ZIKV viremia varies over several orders of magnitude, with unknown consequences for transmission. To determine the effect of viral concentration on ZIKV transmission risk, we exposed field-derived Ae. aegypti mosquitoes to four doses (10³, 10⁴, 10⁵, 10⁶ PFU/mL) representative of potential variation in the field. We demonstrate that increasing ZIKV dose in the blood-meal significantly increases the probability of mosquitoes becoming infected, and consequently disseminating virus and becoming infectious. Additionally, we observed significant interactions between dose and days post-infection on dissemination and overall transmission efficiency, suggesting that variation in ZIKV dose affects the rates of midgut escape and salivary gland invasion. We did not find significant effects of dose on mosquito mortality. We also demonstrate that detecting virus using RT-qPCR approaches rather than plaque assays potentially over-estimates key transmission parameters, including the time at which mosquitoes become infectious and viral burden. Finally, using these data to parameterize an R₀ model, we showed that increasing viremia from 10⁴ to 10⁶ PFU/mL increased relative R₀ 3.8-fold, demonstrating that variation in viremia substantially affects transmission risk.

The number of people at risk for contracting Zika virus (ZIKV) is difficult to estimate accurately because most infected hosts are asymptomatic and the relationship between variation in host viremia and transmission to local mosquitoes is unclear. Controlling ZIKV transmission remains a major challenge due to lack of basic information on transmission mechanisms and gaps in mechanistic models. Therefore, our study highlights the importance of variation in viral concentration that current modeling efforts ignore, which will enhance our ability to predict the number of people at risk for arbovirus infection, overall disease transmission, and the efficacy of current and future intervention strategies. We demonstrated that increased concentration of ZIKV in the blood significantly increases the probability and the rate at which mosquitoes become infectious, which increases the risk of ZIKV transmission.

Studying the effects of emerging infections on the fetus: Experience with West Nile and Zika viruses

Emerging infections have the potential to produce adverse effects on the pregnant woman or her fetus; however, studying these effects is often challenging. We review our experiences with investigating the prenatal effects of two mosquito‐borne infections that emerged in the past 2 decades, West Nile virus (WNV) and Zika virus. Concerns regarding teratogenicity were raised about both viruses; Zika virus has been confirmed to be teratogenic, while WNV appears not to increase the risk for adverse outcomes, although teratogenicity has not been excluded. Study designs used to examine the effects of both viruses include case reports and series, pregnancy registries, and cohort studies. Case–control studies and birth defects surveillance systems are being used to study the effects during pregnancy of Zika virus, but not the effects of WNV, because a specific phenotype was observed among infants with congenital Zika infection, but not among infants with congenital WNV infection. Experimental data that demonstrated that Zika virus was neurotropic have also been useful because they provided biologic plausibility for Zika virus's teratogenic effects: these findings were consistent with observations in congenitally infected infants. Challenges encountered with studies to evaluate the effects of these infections include the broad range of possible adverse outcomes, the inability to include all infected pregnant women in studies because many infections are asymptomatic, and the difficulty with interpretation of diagnostic testing of infants (WNV and Zika) and pregnant women (Zika). This review might be helpful to guide future studies of the effects of emerging infections during pregnancy. Birth Defects Research 109:363–371, 2017. © 2017 Wiley Periodicals, Inc.

Establishing Mouse Models for Zika Virus-induced Neurological Disorders Using Intracerebral Injection Strategies: Embryonic, Neonatal, and Adult

The Zika virus (ZIKV) is a flavivirus currently endemic in North, Central, and South America. It is now established that the ZIKV can cause microcephaly and additional brain abnormalities. However, the mechanism underlying the pathogenesis of ZIKV in the developing brain remains unclear. Intracerebral surgical methods are frequently used in neuroscience research to address questions about both normal and abnormal brain development and brain function. This protocol utilizes classical surgical techniques and describes methods that allow one to model ZIKV-associated human neurological disease in the mouse nervous system. While direct brain inoculation does not model the normal mode of virus transmission, the method allows investigators to ask targeted questions concerning the consequence after ZIKV infection of the developing brain. This protocol describes embryonic, neonatal, and adult stages of intraventricular inoculation of ZIKV. Once mastered, this method can become a straightforward and reproducible technique that only takes a few hours to perform.

Recent Advances in Animal Models of Zika Virus Infection

An infection by Zika virus (ZIKV), a mosquito-borne flavivirus, broke out in South American regions in 2015, and recently showed a tendency of spreading to North America and even worldwide. ZIKV was first detected in 1947 and only 14 human infection cases were reported until 2007. This virus was previously observed to cause only mild flu-like symptoms. However, recent ZIKV infections might be responsible for the increasing cases of neurological disorders such as Guillain-Barré syndrome and congenital defects, including newborn microcephaly. Therefore, researchers have established several animal models to study ZIKV transmission and pathogenesis, and test therapeutic candidates. This review mainly summarizes the reported animal models of ZIKV infection, including mice and non-human primates.

Zika virus infection as a cause of congenital brain abnormalities and Guillain-Barré syndrome: From systematic review to living systematic review

Background. The Zika virus (ZIKV) outbreak in the Americas has caused international concern due to neurological sequelae linked to the infection, such as microcephaly and Guillain-Barré syndrome (GBS). The World Health Organization stated that there is “sufficient evidence to conclude that Zika virus is a cause of congenital abnormalities and is a trigger of GBS”. This conclusion was based on a systematic review of the evidence published until 30.05.2016. Since then, the body of evidence has grown substantially, leading to this update of that systematic review with new evidence published from 30.05.2016 – 18.01.2017, update 1.

Methods. We review evidence on the causal link between ZIKV infection and adverse congenital outcomes and the causal link between ZIKV infection and GBS or immune-mediated thrombocytopaenia purpura. We also describe the transition of the review into a living systematic review, a review that is continually updated.

Results. Between 30.05.2016 and 18.01.2017, we identified 2413 publications, of which 101 publications were included. The evidence added in this update confirms the conclusion of a causal association between ZIKV and adverse congenital outcomes. New findings expand the evidence base in the dimensions of biological plausibility, strength of association, animal experiments and specificity. For GBS, the body of evidence has grown during the search period for update 1, but only for dimensions that were already populated in the previous version. There is still a limited understanding of the biological pathways that potentially cause the occurrence of autoimmune disease following ZIKV infection.

Conclusions. This systematic review confirms previous conclusions that ZIKV is a cause of congenital abnormalities, including microcephaly, and is a trigger of GBS. The transition to living systematic review techniques and methodology provides a proof of concept for the use of these methods to synthesise evidence about an emerging pathogen such as ZIKV.

Niclosamide rescues microcephaly in a humanized in vivo model of Zika infection using human induced neural stem cells

Zika virus (ZIKV) is a mosquito-transmitted flavivirus with a causative link to microcephaly, a condition resulting in reduced cranial size and brain abnormalities. Despite recent progress, there is a current lack of in vivo models that permit the study of systemic virus on human neurons in a developing organism that replicates the pathophysiology of human disease. Furthermore, no treatment to date has been reported to reduce ZIKV-induced microcephaly. We tested the effects of ZIKV on human induced neural stem cells (hiNSCs) in vitro and found that infected hiNSCs secrete inflammatory cytokines, display altered differentiation, and become apoptotic. We also utilized this in vitro system to assess the therapeutic effects of niclosamide, an FDA-approved anthelminthic, and found that it decreases ZIKV production, partially restores differentiation, and prevents apoptosis in hiNSCs. We intracranially injected hiNSCs into developing chicks, subjected them to systemic ZIKV infection via the chorioallantoic membrane (CAM), a tissue similar in structure and function to the mammalian placenta, and found that humanized ZIKV-infected embryos developed severe microcephaly including smaller crania, decreased forebrain volume and enlarged ventricles. Lastly, we utilized this humanized model to show that CAM-delivery of niclosamide can partially rescue ZIKV-induced microcephaly and attenuate infection of hiNSCs in vivoThis article has an associated First Person interview with the first author of the paper.

Auditory brainstem function in microcephaly related to Zika virus infection

OBJECTIVE

To study the effect of prenatal Zika virus (ZV) infection on brainstem function reflected in brainstem auditory evoked potentials (BAEPs).

METHODS

In a cross-sectional study in 19 children (12 girls) with microcephaly related to ZV infection, aged between 12 and 62 weeks, the brainstem function was examined through BAEPs. The latencies of wave peaks I, III, and V of the left and right ears (n = 37) were standardized according to normative data, and compared between them by 2-tailed t test. The confounding variables (cephalic perimeter at the born and chronological age) were correlated with the normalized latencies using Pearson test.

RESULTS

All patients showed, in general, clear waveforms, with latencies within 3 SDs of the normative values. However, statistically increased latencies of waves I and III (I > III, p = 0.031) were observed, relative to wave V (p < 0.001), the latter being closer to respective normative value. The latency of wave I was observed to increase with age (r = 0.45, p = 0.005). The waves, in turn, did not depend on cephalic perimeter.

CONCLUSIONS

These results are consistent with the functional normality of the brainstem structure and its lack of correlation with microcephaly, suggesting that the disruption produced by the ZV infection does not act in the cell proliferation phase, but mostly in the processes of neuronal migration and differentiation in the telencephalon.