Zika virus enhances monocyte adhesion and transmigration favoring viral dissemination to neural cells

Zebrafish as a Translational Model: An Experimental Alternative to Study the Mechanisms Involved in Anosmia and Possible Neurodegenerative Aspects of COVID-19?

The Coronavirus disease-2019 (COVID-19) presents a variability of clinical symptoms, ranging from asymptomatic to severe respiratory and systemic conditions. In a cohort of patients, the Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2), beyond the classical respiratory manifestations, induces anosmia. Evidence has suggested SARS-CoV-2-induced anosmia can be the result of neurodegeneration of the olfactory pathway. Neurologic symptoms associated with COVID-19 have been reported; however, the precise mechanism and possible long-lasting effects remain poorly investigated. Preclinical models are valuable tools for describing and testing new possible treatments for neurologic disorders. In this way, the zebrafish (Danio rerio) organism model represents an attractive tool in the field of neuroscience, showing economic and logistic advantages besides genetic and physiologic similarities with mammalian, including the brain structure and functions. Besides, its external embryonic development, high availability of eggs, and fast development allows easy genetic manipulation and fast replications. In the present review, we suggest that the zebrafish model can be advantageous to investigate the neurologic features of COVID-19.

Genomic diversity contributes to the neuroinvasiveness of the Yellow fever French neurotropic vaccine

Mass vaccination with the live attenuated vaccine YF-17D is the current way to prevent infection with Yellow fever virus (YFV). However, 0.000012-0.00002% of vaccinated patients develop post-vaccination neurological syndrome (YEL-AND). Understanding the factors responsible for neuroinvasion, neurotropism, and neurovirulence of the vaccine is critical for improving its biosafety. The YF-FNV vaccine strain, known to be associated with a higher frequency of YEL-AND (0.3-0.4%) than YF-17D, is an excellent model to study vaccine neuroinvasiveness. We determined that neuroinvasiveness of YF-FNV occured both via infection and passage through human brain endothelial cells. Plaque purification and next generation sequencing (NGS) identified several neuroinvasive variants. Their neuroinvasiveness was not higher than that of YF-FNV. However, rebuilding the YF-FNV population diversity from a set of isolated YF-FNV-N variants restored the original neuroinvasive phenotype of YF-FNV. Therefore, we conclude that viral population diversity is a critical factor for YFV vaccine neuroinvasiveness.

Zika Virus Infection of Human Iris Pigment Epithelial Cells

During recent Zika epidemics, adults infected with Zika virus (ZIKV) have developed organ-specific inflammatory complications. The most serious Zika-associated inflammatory eye disease is uveitis, which is commonly anterior in type, affecting both eyes and responding to corticosteroid eye drops. Mechanisms of Zika-associated anterior uveitis are unknown, but ZIKV has been identified in the aqueous humor of affected individuals. The iris pigment epithelium is a target cell population in viral anterior uveitis, and it acts to maintain immune privilege within the anterior eye. Interactions between ZIKV and human iris pigment epithelial cells were investigated with infectivity assays and RNA-sequencing. Primary cell isolates were prepared from eyes of 20 cadaveric donors, and infected for 24 hours with PRVABC59 strain ZIKV or incubated uninfected as control. Cytoimmunofluorescence, RT-qPCR on total cellular RNA, and focus-forming assays of culture supernatant showed cell isolates were permissive to infection, and supported replication and release of infectious ZIKV. To explore molecular responses of cell isolates to ZIKV infection at the whole transcriptome level, RNA was sequenced on the Illumina NextSeq 500 platform, and results were aligned to the human GRCh38 genome. Multidimensional scaling showed clear separation between transcriptomes of infected and uninfected cell isolates. Differential expression analysis indicated a vigorous molecular response of the cell to ZIKV: 7,935 genes were differentially expressed between ZIKV-infected and uninfected cells (FDR < 0.05), and 99% of 613 genes that changed at least two-fold were up-regulated. Reactome and KEGG pathway and Gene Ontology enrichment analyses indicated strong activation of viral recognition and defense, in addition to biosynthesis processes. A CHAT network included 6275 molecular nodes and 24 contextual hubs in the cell response to ZIKV infection. Receptor-interacting serine/threonine kinase 1 (RIPK1) was the most significantly connected contextual hub. Correlation of gene expression with read counts assigned to the ZIKV genome identified a negative correlation between interferon signaling and viral load across isolates. This work represents the first investigation of mechanisms of Zika-associated anterior uveitis using an in vitro human cell model. The results suggest the iris pigment epithelium mounts a molecular response that limits intraocular pathology in most individuals.

Immune cells enhance Zika virus-mediated neurologic dysfunction in brain of mice with humanized immune systems

Zika virus (ZIKV) can generate a number of neurological dysfunctions in infected humans. Here, we tested the potential of human immune cells to protect against ZIKV infection in genetically humanized MISTRG mice. FACS analysis showed robust reconstitution of the mouse spleen with human T cells. Peripheral ZIKV inoculation resulted in infection within the brains of MISTRG mice. Mice that were reconstituted with human peripheral blood mononuclear cells (PBMC) showed a more rapid lethal response to ZIKV than the control mice lacking these immune cells. Immunocytochemical analysis of T cell markers CD3, CD45, or CD8 showed strong T cell presence in the brain, together with robust infection by ZIKV particularly in the excitatory pyramidal and granule neurons of the hippocampus. Infection was also found in cortex, striatum, the dopamine neurons of the substantia nigra, and other brain loci. Infection was considerably less in other regions such as the septum and hypothalamus. These data support the perspective that, rather than exerting a protective function, T cells may underlie some ZIKV-mediated neuropathology in the brain.

Tembusu Virus entering the central nervous system caused nonsuppurative encephalitis without disrupting the blood-brain barrier

Tembusu Virus (TMUV) is an emerging and re-emerging zoonotic pathogen that adversely affects poultry industry in recent years. TMUV disease is characterized by nonsuppurative encephalitis in ducklings. The duckling infection model was established to study the mechanism of TMUV crossing the blood-brain barrier (BBB) into the central nervous system (CNS). Here, we showed that no obvious clinical symptoms and enhancement of BBB permeability occurred at the early stage of infection (3∼5 dpi). While simultaneously virus particles were observed by transmission electron microscopy in the brain, inducing the accumulation of inflammatory cytokines. Neurological symptoms and disruption of BBB appeared at the intermediate stage of infection (7∼9 dpi). It was confirmed that TMUV could survive and propagate in brain microvascular endothelial cells (BMECs), but did not affect the permeability of BBB in vivo and in vitro at an early date. In conclusion, TMUV enters the CNS then causes encephalitis, and finally destruct the BBB, which may be due to the direct effect of TMUV on BMECs and the subsequent response of "inflammatory storm".IMPORTANCE The TMUV disease has caused huge losses to the poultry industry in Asia, which is potentially harmful to public health. Neurological symptoms and their sequelae are the main characters of this disease. However, the mechanism of how this virus enters the brain and causes encephalitis is unclear. In this study, we confirmed that the virus entered the CNS and then massively destroyed BBB and the BBB damage was closely associated with the subsequent outbreak of inflammation. TMUV may enter the CNS through the transcellular and "Trojan horse" pathways. These findings can fill the knowledge gap in the pathogenesis of TMUV-infected poultry and be benefit for the treatment of TMUV disease. What's more, TMUV is a representative to study the infection of avian flavivirus. Therefore, our studies have significances both for understanding of the full scope of mechanisms of TMUV and other flavivirus infection, and conceivably, for therapeutics.

Severe acute respiratory syndrome coronavirus 2 infection reaches the human nervous system: How?

Without protective and/or therapeutic agents the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection known as coronavirus disease 2019 is quickly spreading worldwide. It has surprising transmissibility potential, since it could infect all ages, gender, and human sectors. It attacks respiratory, gastrointestinal, urinary, hepatic, and endovascular systems and can reach the peripheral nervous system (PNS) and central nervous system (CNS) through known and unknown mechanisms. The reports on the neurological manifestations and complications of the SARS-CoV-2 infection are increasing exponentially. Herein, we enumerate seven candidate routes, which the mature or immature SARS-CoV-2 components could use to reach the CNS and PNS, utilizing the within-body cross talk between organs. The majority of SARS-CoV-2-infected patients suffer from some neurological manifestations (e.g., confusion, anosmia, and ageusia). It seems that although the mature virus did not reach the CNS or PNS of the majority of patients, its unassembled components and/or the accompanying immune-mediated responses may be responsible for the observed neurological symptoms. The viral particles and/or its components have been specifically documented in endothelial cells of lung, kidney, skin, and CNS. This means that the blood-endothelial barrier may be considered as the main route for SARS-CoV-2 entry into the nervous system, with the barrier disruption being more logical than barrier permeability, as evidenced by postmortem analyses.

COVID-19: Molecular and Cellular Response

In late December 2019, a vtiral pneumonia with an unknown agent was reported in Wuhan, China. A novel coronavirus was identified as the causative agent. Because of the human-to-human transmission and rapid spread; coronavirus disease 2019 (COVID-19) has rapidly increased to an epidemic scale and poses a severe threat to human health; it has been declared a public health emergency of international concern (PHEIC) by the World Health Organization (WHO). This review aims to summarize the recent research progress of COVID-19 molecular features and immunopathogenesis to provide a reference for further research in prevention and treatment of SARS coronavirus2 (SARS-CoV-2) infection based on the knowledge from researches on SARS-CoV and Middle East respiratory syndrome-related coronavirus (MERS-CoV).

Micro-Meta App: an interactive tool for collecting microscopy metadata based on community specifications

For quality, interpretation, reproducibility and sharing value, microscopy images should be accompanied by detailed descriptions of the conditions that were used to produce them. Micro-Meta App is an intuitive, highly interoperable, open-source software tool that was developed in the context of the 4D Nucleome (4DN) consortium and is designed to facilitate the extraction and collection of relevant microscopy metadata as specified by the recent 4DN-BINA-OME tiered-system of Microscopy Metadata specifications. In addition to substantially lowering the burden of quality assurance, the visual nature of Micro-Meta App makes it particularly suited for training purposes.

Modeling SARS-CoV-2 infection in individuals with opioid use disorder with brain organoids

The COVID-19 pandemic has aggravated a preexisting epidemic: the opioid crisis. Much literature has shown that the circumstances imposed by COVID-19, such as social distancing regulations, medical and financial instability, and increased mental health issues, have been detrimental to those with opioid use disorder (OUD). In addition, unexpected neurological sequelae in COVID-19 patients suggest that COVID-19 compromises neuroimmunity, induces hypoxia, and causes respiratory depression, provoking similar effects as those caused by opioid exposure. Combined conditions of COVID-19 and OUD could lead to exacerbated complications. With limited human in vivo options to study these complications, we suggest that iPSC-derived brain organoid models may serve as a useful platform to investigate the physiological connection between COVID-19 and OUD. This mini-review highlights the advances of brain organoids in other neuropsychiatric and infectious diseases and suggests their potential utility for investigating OUD and COVID-19, respectively.

S100A4+ macrophages facilitate zika virus invasion and persistence in the seminiferous tubules via interferon-gamma mediation

Testicular invasion and persistence are features of Zika virus (ZIKV), but their mechanisms are still unknown. Here, we showed that S100A4+ macrophages, a myeloid macrophage subpopulation with susceptibility to ZIKV infection, facilitated ZIKV invasion and persistence in the seminiferous tubules. In ZIKV-infected mice, S100A4+ macrophages were specifically recruited into the interstitial space of testes and differentiated into interferon-γ-expressing M1 macrophages. With interferon-γ mediation, S100A4+ macrophages down-regulated Claudin-1 expression and induced its redistribution from the cytosol to nucleus, thus increasing the permeability of the blood-testis barrier which facilitated S100A4+ macrophages invasion into the seminiferous tubules. Intraluminal S100A4+ macrophages were segregated from CD8+ T cells and consequently helped ZIKV evade cellular immunity. As a result, ZIKV continued to replicate in intraluminal S100A4+ macrophages even when the spermatogenic cells disappeared. Deficiencies in S100A4 or interferon-γ signaling both reduced ZIKV infection in the seminiferous tubules. These results demonstrated crucial roles of S100A4+ macrophages in ZIKV infection in testes.

CNS implications of COVID-19: a comprehensive review

COVID-19 was first reported in December 2019 in the Wuhan city of China, and since then it has spread worldwide taking a heavy toll on human life and economy. COVID-19 infection is commonly associated with symptoms like coughing, fever, and shortness of breath, besides, the reports of muscle pain, anosmia, hyposmia, and loss of taste are becoming evident. Recent reports suggest the pathogenic invasion of the SARS-CoV-2 into the CNS, that could thereby result in devastating long term complications, primarily because some of these complications may go unnoticed for a long time. Evidence suggest that the virus could enter the CNS through angiotensin-converting enzyme-2 (ACE-2) receptor, neuronal transport, haematogenous route, and nasal route via olfactory bulb, cribriform plate, and propagates through trans-synaptic signalling, and shows retrograde movement into the CNS along nerve fiber. COVID-19 induces CNS inflammation and neurological degenerative damage through a diverse mechanism which includes ACE-2 receptor damage, cytokine-associated injury or cytokine storm syndrome, secondary hypoxia, demyelination, blood-brain barrier disruption, neurodegeneration, and neuroinflammation. Viral invasion into the CNS has been reported to show association with complications like Parkinsonism, Alzheimer's disorder, meningitis, encephalopathy, anosmia, hyposmia, anxiety, depression, psychiatric symptoms, seizures, stroke, etc. This review provides a detailed discussion of the CNS pathogenesis of COVID-19. Authors conclude that the COVID-19 cannot just be considered as a disorder of the pulmonary or peripheral system, rather it has a significant CNS involvement. Therefore, CNS aspects of the COVID-19 should be monitored very closely to prevent long term CNS complications, even after the patient has recovered from COVID-19.

Evidence That Zika Virus Is Transmitted by Breastfeeding to Newborn A129 (Ifnar1 Knock-Out) Mice and Is Able to Infect and Cross a Tight Monolayer of Human Intestinal Epithelial Cells

Zika virus (ZIKV) belongs to the Flavivirus genus in the Flaviviridae family. Mainly transmitted via mosquito bites (Aedes aegypti, Aedes albopictus), ZIKV has been classified in the large category of arthropod-borne viruses, or arboviruses. However, during the past two outbreaks in French Polynesia (2013–2014) and Latin America (2015–2016), several cases of ZIKV human-to-human transmission were reported, either vertically via transplacental route but also horizontally after sexual intercourse. Interestingly, high viral burdens were detected in the colostrum and breast milk of infected women and mother-to-child transmission of ZIKV during breastfeeding was recently highlighted. In a previous study, we highlighted the implication of the mammary epithelium (blood–milk barrier) in ZIKV infectious particles excretion in breast milk. However, mechanisms of their further transmissibility to the newborn via oral route through contaminated breast milk remain unknown. In this study, we provide the first experimental proof-of-concept of the existence of the breastfeeding as a route for mother-to-child transmission of ZIKV and characterized the neonatal oral transmission in a well-established mouse model of ZIKV infection. From a mechanistical point-of-view, we demonstrated for the first time that ZIKV was able to infect and cross an in vitro model of tight human intestinal epithelium without altering its barrier integrity, permitting us to consider the gut as an entry site for ZIKV after oral exposure. By combining in vitro and in vivo experiments, this study strengthens the plausibility of mother-to-child transmission of ZIKV during breastfeeding and helps to better characterize underlying mechanisms, such as the crossing of the newborn intestinal epithelium by ZIKV. As a consequence, these data could serve as a basis for a reflection about the implementation of measures to prevent ZIKV transmission, while keeping in mind breastfeeding-associated benefits.

Zika Virus Replication in Myeloid Cells during Acute Infection Is Vital to Viral Dissemination and Pathogenesis in a Mouse Model

Zika virus (ZIKV) can establish infection in immune privileged sites such as the testes, eye, and placenta. Whether ZIKV infection of white blood cells is required for dissemination of the virus to immune privileged sites has not been definitively shown. To assess whether initial ZIKV replication in myeloid cell populations is critical for dissemination during acute infection, recombinant ZIKVs were generated that could not replicate in these specific cells. ZIKV was cell restricted by insertion of a complementary sequence to a myeloid-specific microRNA in the 3' untranslated region. Following inoculation of a highly sensitive immunodeficient mouse model, crucial immune parameters, such as quantification of leukocyte cell subsets, cytokine and chemokine secretion, and viremia, were assessed. Decreased neutrophil numbers in the spleen were observed during acute infection with myeloid-restricted ZIKV that precluded the generation of viremia and viral dissemination to peripheral organs. Mice inoculated with a nontarget microRNA control ZIKV demonstrated increased expression of key cytokines and chemokines critical for neutrophil and monocyte recruitment and increased neutrophil influx in the spleen. In addition, ZIKV-infected Ly6Chi monocytes were identified in vivo in the spleen. Mice inoculated with myeloid-restricted ZIKV had a decrease in Ly6Chi ZIKV RNA-positive monocytes and a lack of inflammatory cytokine production compared to mice inoculated with control ZIKV.IMPORTANCE Myeloid cells, including monocytes, play a crucial role in immune responses to pathogens. Monocytes have also been implicated as "Trojan horses" during viral infections, carrying infectious virus particles to immune privileged sites and/or to sites protected by physical blood-tissue barriers, such as the blood-testis barrier and the blood-brain barrier. In this study, we found that myeloid cells are crucial to Zika virus (ZIKV) pathogenesis. By engineering ZIKV clones to encode myeloid-specific microRNA target sequences, viral replication was inhibited in myeloid cells by harnessing the RNA interference pathway. Severely immunodeficient mice inoculated with myeloid-restricted ZIKV did not demonstrate clinical signs of disease and survived infection. Furthermore, viral dissemination to peripheral organs was not observed in these mice. Lastly, we identified Ly6Cmid/hi murine monocytes as the major myeloid cell population that disseminates ZIKV.

Modelling of pathogen-host systems using deeper ORF annotations and transcriptomics to inform proteomics analyses

The Zika virus is a flavivirus that can cause fulminant outbreaks and lead to Guillain-Barré syndrome, microcephaly and fetal demise. Like other flaviviruses, the Zika virus is transmitted by mosquitoes and provokes neurological disorders. Despite its risk to public health, no antiviral nor vaccine are currently available. In the recent years, several studies have set to identify human host proteins interacting with Zika viral proteins to better understand its pathogenicity. Yet these studies used standard human protein sequence databases. Such databases rely on genome annotations, which enforce a minimal open reading frame (ORF) length criterion. An ever-increasing number of studies have demonstrated the shortcomings of such annotation, which overlooks thousands of functional ORFs. Here we show that the use of a customized database including currently non-annotated proteins led to the identification of 4 alternative proteins as interactors of the viral capsid and NS4A proteins. Furthermore, 12 alternative proteins were identified in the proteome profiling of Zika infected monocytes, one of which was significantly up-regulated. This study presents a computational framework for the re-analysis of proteomics datasets to better investigate the viral-host protein interplays upon infection with the Zika virus.

Tracking Mechanisms of Viral Dissemination In Vivo

Dissemination and replication of viruses into hosts is a multistep process where viral particles infect, navigate, and indoctrinate various cell types. Viruses can reach tissues that are distant from their infection site by subverting subcellular mechanisms in ways that are, sometimes, disruptive. Modeling these steps, at appropriate resolution and within animal models, is cumbersome. Yet, mimicking these strategies in vitro fails to recapitulate the complexity of the cellular ecosystem. Here, we will discuss relevant in vivo platforms to dissect the cellular and molecular programs governing viral dissemination and briefly discuss organoid and ex vivo alternatives. We will focus on the zebrafish model and will describe how it provides a transparent window to unravel new cellular mechanisms of viral dissemination in vivo.

The zebrafish model allows in vivo investigations of virus-induced molecular processes at subcellular resolution.

Viruses have evolved multiple strategies for disseminating over long distance, including by indoctrinating host cell types with high migration potential.

Organoids derived from stem cells emerge as powerful alternatives to unravel new molecular mechanisms of viral dissemination.

Zika Virus Infection Promotes Local Inflammation, Cell Adhesion Molecule Upregulation, and Leukocyte Recruitment at the Blood-Brain Barrier

The blood-brain barrier (BBB) largely prevents toxins and pathogens from accessing the brain. Some viruses have the ability to cross this barrier and replicate in the central nervous system (CNS). Zika virus (ZIKV) was responsible in 2015 to 2016 for a major epidemic in South America and was associated in some cases with neurological impairments. Here, we characterized some of the mechanisms behind its neuroinvasion using an innovative in vitro human BBB model. ZIKV efficiently replicated, was released on the BBB parenchyma side, and triggered subtle modulation of BBB integrity as well as an upregulation of inflammatory and cell adhesion molecules (CAMs), which in turn favored leukocyte recruitment. Finally, we showed that ZIKV-infected mouse models displayed similar CAM upregulation and that soluble CAMs were increased in plasma samples from ZIKV-infected patients. Our observations suggest a complex interplay between ZIKV and the BBB, which may trigger local inflammation, leukocyte recruitment, and possible cerebral vasculature impairment.IMPORTANCE Zika virus (ZIKV) can be associated with neurological impairment in children and adults. To reach the central nervous system, viruses have to cross the blood-brain barrier (BBB), a multicellular system allowing a tight separation between the bloodstream and the brain. Here, we show that ZIKV infects cells of the BBB and triggers a subtle change in its permeability. Moreover, ZIKV infection leads to the production of inflammatory molecules known to modulate BBB integrity and participate in immune cell attraction. The virus also led to the upregulation of cellular adhesion molecules (CAMs), which in turn favored immune cell binding to the BBB and potentially increased infiltration into the brain. These results were also observed in a mouse model of ZIKV infection. Furthermore, plasma samples from ZIKV-infected patients displayed an increase in CAMs, suggesting that this mechanism could be involved in neuroinflammation triggered by ZIKV.

Identification of a DNA Aptamer That Binds to Human Monocytes and Macrophages

As cancer strategies shift toward immunotherapy, the need for new binding ligands to target and isolate specific immune cell populations has soared. Based on prior work identifying a peptide specific for murine M2-like macrophages, we sought to identify an aptamer that could bind human M2-like macrophages. Tumor-associated macrophages (TAMs) adopt an M2-like phenotype and support tumor progression and dissemination. Here, we employed cell-SELEX to identify an aptamer ligand that targets this cell population over tissue resident (M0-like) or tumoricidal (M1-like) macrophages. Instead, we identified an aptamer that binds both human M0- and M2-like macrophages and monocytes, with highest binding affinity to M2-like macrophage (K_d ∼ 20 nM) and monocytes (K_d ∼ 45 nM) and minimal binding to other leukocytes. The aptamer binds to CD14⁺ but not CD16⁺ monocytes, and is rapidly internalized by these cells. We also demonstrate that this aptamer is able to bind human monocytes when both are administered in vivo to mice. Thus, binding to these cell populations (monocytes, M0-like and M2-like macrophages), this aptamer lends itself toward monocyte-specific applications, such as monocyte-targeted drug delivery or column selection.

Potential of SARS-CoV-2 to Cause CNS Infection: Biologic Fundamental and Clinical Experience

SARS-CoV-2 is a novel coronavirus leading to serious respiratory disease and is spreading around the world at a raging speed. Recently there is emerging speculations that the central nervous system (CNS) may be involved during SARS-CoV-2 infection, contributing to the respiratory failure. However, the existence of viral replication in CNS has not been confirmed due to the lack of evidence from autopsy specimens. Considering the tropism of SARS-CoV-2, ACE2, is prevailing in CNS, and the neuro-invasive property of human coronavirus was widely reported, there is a need to identified the possible complications during COVID-19 for CNS. In this review, we conduct a detailed summary for the potential of SARS-CoV-2 to infect central nervous system from latest biological fundamental of SARS-CoV-2 to the clinical experience of other human coronaviruses. To confirm the neuro-invasive property of SARS-CoV-2 and the subsequent influence on patients will require further exploration by both virologist and neurologist.

Modeling neurological disorders using brain organoids

Neurological disorders are challenging to study given the complexity and species-specific features of the organ system. Brain organoids are three dimensional structured aggregates of neural tissue that are generated by self-organization and differentiation from pluripotent stem cells under optimized culture conditions. These brain organoids exhibit similar features of structural organization and cell type diversity as the developing human brain, creating opportunities to recapitulate disease phenotypes that are not otherwise accessible. Here we review the initial attempt in the field to apply brain organoid models for the study of many different types of human neurological disorders across a wide range of etiologies and pathophysiologies. Forthcoming advancements in both brain organoid technology as well as analytical methods have significant potentials to advance the understanding of neurological disorders and to uncover opportunities for meaningful therapeutic intervention.

The journey of Zika to the developing brain

Zika virus is a mosquito-borne Flavivirus originally isolated from humans in 1952. Following its re-emergence in Brazil in 2015, an increase in the number of babies born with microcephaly to infected mothers was observed. Microcephaly is a neurodevelopmental disorder, characterised phenotypically by a smaller than average head size, and is usually developed in utero. The 2015 outbreak in the Americas led to the World Health Organisation declaring Zika a Public Health Emergency of International Concern. Since then, much research into the effects of Zika has been carried out. Studies have investigated the structure of the virus, its effects on and evasion of the immune response, cellular entry including target receptors, its transmission from infected mother to foetus and its cellular targets. This review discusses current knowledge and novel research into these areas, in hope of developing a further understanding of how exposure of pregnant women to the Zika virus can lead to impaired brain development of their foetus. Although no longer considered an epidemic in the Americas, the mechanism by which Zika acts is still not comprehensively and wholly understood, and this understanding will be crucial in developing effective vaccines and treatments.

The Differentiation of Human Cytomegalovirus Infected-Monocytes Is Required for Viral Replication

Viral dissemination is a key mechanism responsible for persistence and disease following human cytomegalovirus (HCMV) infection. Monocytes play a pivotal role in viral dissemination to organ tissue during primary infection and following reactivation from latency. For example, during primary infection, infected monocytes migrate into tissues and differentiate into macrophages, which then become a source of viral replication. In addition, because differentiated macrophages can survive for months to years, they provide a potential persistent infection source in various organ systems. We broadly note that there are three phases to infection and differentiation of HCMV-infected monocytes: (1) Virus enters and traffics to the nucleus through a virus receptor ligand engagement event that activates a unique signalsome that initiates the monocyte-to-macrophage differentiation process. (2) Following initial infection, HCMV undergoes a "quiescence-like state" in monocytes lasting for several weeks and promotes monocyte differentiation into macrophages. While, the initial event is triggered by the receptor-ligand engagement, the long-term cellular activation is maintained by chronic viral-mediated signaling events. (3) Once HCMV infected monocytes differentiate into macrophages, the expression of immediate early viral (IE) genes is detectable, followed by viral replication and long term infectious viral particles release. Herein, we review the detailed mechanisms of each phase during infection and differentiation into macrophages and discuss the biological significance of the differentiation of monocytes in the pathogenesis of HCMV.