Zika Virus Infectious Cell Culture System and the In Vitro Prophylactic Effect of Interferons

Assessing the role of Ndel1 oligopeptidase activity in congenital Zika syndrome: Potential predictor of congenital syndrome endophenotype and treatment response

Maternal infections are among the main risk factors for cognitive impairments in the offspring. Zika virus (ZIKV) can be transmitted vertically, causing a set of heterogeneous birth defects, such as microcephaly, ventriculomegaly and corpus callosum dysgenesis. Nuclear distribution element like-1 (Ndel1) oligopeptidase controls crucial aspects of cerebral cortex development underlying cortical malformations. Here, we examine Ndel1 activity in an animal model for ZIKV infection, which was associated with deregulated corticogenesis. We observed here a reduction in Ndel1 activity in the forebrain associated with the congenital syndrome induced by ZIKV isolates, in an in utero and postnatal injections of different inoculum doses in mice models. In addition, we observed a strong correlation between Ndel1 activity and brain size of animals infected by ZIKV, suggesting the potential of this measure as a biomarker for microcephaly. More importantly, the increase of interferon (IFN)-beta signaling, which was used to rescue the ZIKV infection outcomes, also recovered Ndel1 activity to levels similar to those of uninfected healthy control mice, but with no influence on Ndel1 activity in uninfected healthy control animals. Taken together, we demonstrate for the first time here an association of corticogenesis impairments determined by ZIKV infection and the modulation of Ndel1 activity. Although further studies are still necessary to clarify the possible role(s) of Ndel1 activity in the molecular mechanism(s) underlying the congenital syndrome induced by ZIKV, we suggest here the potential of monitoring the Ndel1 activity to predict this pathological condition at early stages of embryos or offspring development, during while the currently employed methods are unable to detect impaired corticogenesis leading to microcephaly. Ndel1 activity may also be possibly used to follow up the positive response to the treatment, such as that employing the IFN-beta that is able to rescue the ZIKV-induced brain injury.

Survival and Replication of Zika Virus in Diapause Eggs of Aedes Albopictus From Beijing, China

Zika virus (ZIKV) has emerged as a globally important arbovirus. The virus is primarily transmitted to humans through the bite of an infective Aedes albopictus in temperate area. Vertical transmission of ZIKV by Ae. albopictus is determined and has been suggested to be a means by which the virus could persist in nature. Ae. albopictus undergoes a well-characterized photoperiodic diapause. Viruses are harbored by overwintering mosquitoes in diapause that contributes to the resurgence of vertebrate diseases in the following spring, yet little is known about the impact of diapause on the regulation of viral replication and survival. The purpose of this study is to determine that Ae. albopictus in Beijing are highly susceptible to ZIKV (92.3%), and viable virus is passed to their organs of progeny via vertical transmission. Moreover, diapause eggs (diapause incidence 97.8%) had significantly lower minimum infection rates and filial infection rates of the first gonotrophic cycle than those of the second gonotrophic cycle in the short-day photoperiod group. Regarding the development of diapause eggs, the minimum infection rates and ZIKV RNA copy number increased significantly, suggesting that virus RNA replication occurred in the diapause eggs. Meanwhile, eggs from the ZIKV-infected mosquitoes had a significantly lower hatching rate compared with uninfected mosquitoes, implying an intriguing interaction between diapause eggs and virus. The findings here suggest that vertical transmission of ZIKV from diapause eggs to progeny may have a critical epidemiological role in the dissemination and maintenance of ZIKV circulating in the vector.

A platform of assays for the discovery of anti-Zika small-molecules with activity in a 3D-bioprinted outer-blood-retina model

The global health emergency posed by the outbreak of Zika virus (ZIKV), an arthropod-borne flavivirus causing severe neonatal neurological conditions, has subsided, but there continues to be transmission of ZIKV in endemic regions. As such, there is still a medical need for discovering and developing therapeutical interventions against ZIKV. To identify small-molecule compounds that inhibit ZIKV disease and transmission, we screened multiple small-molecule collections, mostly derived from natural products, for their ability to inhibit wild-type ZIKV. As a primary high-throughput screen, we used a viral cytopathic effect (CPE) inhibition assay conducted in Vero cells that was optimized and miniaturized to a 1536-well format. Suitably active compounds identified from the primary screen were tested in a panel of orthogonal assays using recombinant Zika viruses, including a ZIKV Renilla luciferase reporter assay and a ZIKV mCherry reporter system. Compounds that were active in the wild-type ZIKV inhibition and ZIKV reporter assays were further evaluated for their inhibitory effects against other flaviviruses. Lastly, we demonstrated that wild-type ZIKV is able to infect a 3D-bioprinted outer-blood-retina barrier tissue model and disrupt its barrier function, as measured by electrical resistance. One of the identified compounds (3-Acetyl-13-deoxyphomenone, NCGC00380955) was able to prevent the pathological effects of the viral infection on this clinically relevant ZIKV infection model.

Zika virus baculovirus-expressed envelope protein elicited humoral and cellular immunity in immunocompetent mice

Zika virus (ZIKV) is a mosquito-borne virus that has a high risk of inducing Guillain-Barré syndrome and microcephaly in newborns. Because vaccination is considered the most effective strategy against ZIKV infection, we designed a recombinant vaccine utilizing the baculovirus expression system with two strains of ZIKV envelope protein (MR766, Env_M; ZBRX6, Env_Z). Animals inoculated with Env_M and Env_Z produced ZIKV-specific antibodies and secreted effector cytokines such as interferon-γ, tumor necrosis factor-α, and interleukin-12. Moreover, the progeny of immunized females had detectable maternal antibodies that protected them against two ZIKV strains (MR766 and PRVABC59) and a Dengue virus strain. We propose that the baculovirus expression system ZIKV envelope protein recombinant provides a safe and effective vaccine strategy.

Organoid modeling of Zika and herpes simplex virus 1 infections reveals virus-specific responses leading to microcephaly

Viral infection in early pregnancy is a major cause of microcephaly. However, how distinct viruses impair human brain development remains poorly understood. Here we use human brain organoids to study the mechanisms underlying microcephaly caused by Zika virus (ZIKV) and herpes simplex virus (HSV-1). We find that both viruses efficiently replicate in brain organoids and attenuate their growth by causing cell death. However, transcriptional profiling reveals that ZIKV and HSV-1 elicit distinct cellular responses and that HSV-1 uniquely impairs neuroepithelial identity. Furthermore, we demonstrate that, although both viruses fail to potently induce the type I interferon system, the organoid defects caused by their infection can be rescued by distinct type I interferons. These phenotypes are not seen in 2D cultures, highlighting the superiority of brain organoids in modeling viral infections. These results uncover virus-specific mechanisms and complex cellular immune defenses associated with virus-induced microcephaly.

Histopathological lesions of congenital Zika syndrome in newborn squirrel monkeys

The absence of an adequate animal model for studies has limited the understanding of congenital Zika syndrome (CZS) in humans during the outbreak in America. In this study, we used squirrel monkeys (Saimiri collinsi), a neotropical primate (which mimics the stages of human pregnancy), as a model of Zika virus (ZIKV) infection. Seven pregnant female squirrel monkeys were experimentally infected at three different gestational stages, and we were able reproduce a broad range of clinical manifestations of ZIKV lesions observed in newborn humans. Histopathological and immunohistochemical analyses of early-infected newborns (2/4) revealed damage to various areas of the brain and ZIKV antigens in the cytoplasm of neurons and glial cells, indicative of CZS. The changes caused by ZIKV infection were intrauterine developmental delay, ventriculomegaly, simplified brain gyri, vascular impairment and neuroprogenitor cell dysfunction. Our data show that the ZIKV infection outcome in squirrel monkeys is similar to that in humans, indicating that this model can be used to help answer questions about the effect of ZIKV infection on neuroembryonic development and the morphological changes induced by CZS.

Prenatal disorders and congenital Zika syndrome in squirrel monkeys

During the Zika virus (ZIKV) outbreak in Brazil (2015–2016), the clinical manifestations associated with its infection were complex and included miscarriage and congenital malformations, not previously described. In this study, we evaluated the prenatal conditions of pregnant female squirrel monkeys (Saimiri collinsi) infected during different gestational thirds (GTs) and assessed all clinical aspects, diagnostic imaging, viremia and the immune response. In our study, 75% of the infected animals in the 1st GT group had significant clinical manifestations, such as miscarriage and prolonged viremia associated with a late immune response. Consequently, their neonates showed fetal neuropathology, such as cerebral hemorrhage, lissencephaly or malformations of the brain grooves, ventriculomegaly, and craniofacial malformations. Thus, our study demonstrated the relevance of pregnant squirrel monkeys as a model for the study of ZIKV infection in neonates due to the broad clinical manifestations presented, including the typical congenital Zika syndrome manifestations described in humans.

Dengue and Zika Viruses: Epidemiological History, Potential Therapies, and Promising Vaccines

Dengue virus (DENV), which can lead to fatal hemorrhagic fever, affects 390 million people worldwide. The closely related Zika virus (ZIKV) causes microcephaly in newborns and Guillain-Barré syndrome in adults. Both viruses are mostly transmitted by Aedes albopictus and Aedes aegypti mosquitoes, which, due to globalization of trade and travel alongside climate change, are spreading worldwide, paving the way to DENV and ZIKV transmission and the occurrence of new epidemics. Local outbreaks have already occurred in temperate climates, even in Europe. As there are no specific treatments, these viruses are an international public health concern. Here, we analyze and discuss DENV and ZIKV outbreaks history, clinical and pathogenesis features, and modes of transmission, supplementing with information on advances on potential therapies and restraining measures. Taking advantage of the knowledge of the structure and biological function of the capsid (C) protein, a relatively conserved protein among flaviviruses, within a genus that includes DENV and ZIKV, we designed and patented a new drug lead, pep14-23 (WO2008/028939A1). It was demonstrated that it inhibits the interaction of DENV C protein with the host lipid system, a process essential for viral replication. Such an approach can be used to develop new therapies for related viruses, such as ZIKV.

The Robust Restriction of Zika Virus by Type-I Interferon in A549 Cells Varies by Viral Lineage and Is Not Determined by IFITM3

Type-I interferon (IFN-I) is a major antiviral host response but its impact on Zika virus (ZIKV) replication is not well defined, particularly as it relates to different circulating strains. Interferon stimulated genes (ISGs) that inhibit ZIKV, such as IFITM3, have been identified largely using overexpression studies. Here, we tested whether diverse ZIKV strains differed in their susceptibility to IFN-I-mediated restriction and the contribution of IFITM3 to this restriction. We identified a robust IFN-I-mediated antiviral effect on ZIKV replication (>100-fold reduction) in A549 cells, a commonly used cell line to study ZIKV replication. The extent of inhibition depended on the IFN-I type and the virus strain tested. Viruses from the American pathogenic outbreak were more sensitive to IFNα (p = 0.049) and IFNβ (p = 0.09) than African-lineage strains, which have not been linked to severe pathogenesis. Knocking out IFITM3 expression did not dampen the IFN-I antiviral effect and only high overexpression of IFITM3 led to ZIKV inhibition. Moreover, IFITM3 expression levels in different cells were not associated with IFN-mediated ZIKV inhibition. Taken together, our findings indicate that there is a robust IFN-I-mediated antiviral effect on ZIKV infection, particularly for American viruses, that is not due to IFITM3. A549 cells, which are a commonly used cell line to study ZIKV replication, present an opportunity for the discovery of novel antiviral ISGs against ZIKV.

Zika Virus Mucosal Infection Provides Protective Immunity

Zika virus (ZIKV) is a major human pathogen. ZIKV can replicate in female and male reproductive organs, thus facilitating the human-human transmission cycle. Viral shedding in the semen can increase the risk of ZIKV transmission through sexual mode. Therefore, the vaginal and anorectal mucosa are relevant sites for ZIKV infection. However, the pathobiology of ZIKV transmission through the rectal route is not well understood. Here, we utilize a mouse model system to investigate the immunopathological consequences following ZIKV infection of the rectal mucosa compared to a subcutaneous route of infection. We show that ZIKV-rectal inoculation results in viremia with subclinical infection. ZIKV infects the mucosal epithelium and submucosal dendritic cells, inducing immune and inflammatory cell infiltration. Rectal transmission of ZIKV resulted in the generation of serum-neutralizing antibody responses. Mass cytometry analyses of splenocytes showed a significantly reduced level of inflammatory monocyte and neutrophil cellular responses in the rectal route group. Furthermore, immunological priming through the rectal mucosa with an attenuated ZIKV strain resulted in significant protection from lethal subcutaneous ZIKV challenge, further eliciting robust memory CD4-positive (CD4+) and CD8+ T-cell and ZIKV-specific serum-neutralizing antibody responses. Thus, our study provides deeper immunopathobiological insights on rectal transmission and highlights a rational strategy for mucosal immunization. This model system recapitulates clinical aspects of human ZIKV disease outcome, where most infections are well controlled and result in subclinical and asymptomatic outcomes.IMPORTANCE Zika virus is a clinically significant human pathogen that is primarily transmitted and spread by Aedes species mosquitoes but is also sexually transmissible. The recent pandemic in the Americas led to an unprecedented increase of newborn babies with developmental brain and eye abnormalities. To date, there is no licensed vaccine or therapeutic intervention available for the fight against ZIKV. Understanding the sexual transmission of ZIKV through vaginal and rectal routes is necessary to restrict virus transmission and spread. This study examines the early immunological and pathological consequences of rectal and subcutaneous routes of ZIKV infection using a mouse model. We characterized the primary target cells of ZIKV infection and the subsequent mucosal immune responses to infection, and we demonstrate the protective effect of mucosal rectal immunization using an attenuated ZIKV strain. This mucosal vaccination approach can be further developed to prevent future ZIKV outbreaks.

Antiviral Activity of Benzavir-2 against Emerging Flaviviruses

Most flaviviruses are arthropod-borne viruses, transmitted by either ticks or mosquitoes, and cause morbidity and mortality worldwide. They are endemic in many countries and have recently emerged in new regions, such as the Zika virus (ZIKV) in South-and Central America, the West Nile virus (WNV) in North America, and the Yellow fever virus (YFV) in Brazil and many African countries, highlighting the need for preparedness. Currently, there are no antiviral drugs available to treat flavivirus infections. We have previously discovered a broad-spectrum antiviral compound, benzavir-2, with potent antiviral activity against both DNA- and RNA-viruses. Our purpose was to investigate the inhibitory activity of benzavir-2 against flaviviruses. We used a ZIKV ZsGreen-expressing vector, two lineages of wild-type ZIKV, and other medically important flaviviruses. Benzavir-2 inhibited ZIKV derived reporter gene expression with an EC₅₀ value of 0.8 ± 0.1 µM. Furthermore, ZIKV plaque formation, progeny virus production, and viral RNA expression were strongly inhibited. In addition, 2.5 µM of benzavir-2 reduced infection in vitro in three to five orders of magnitude for five other flaviviruses: WNV, YFV, the tick-borne encephalitis virus, Japanese encephalitis virus, and dengue virus. In conclusion, benzavir-2 was a potent inhibitor of flavivirus infection, which supported the broad-spectrum antiviral activity of benzavir-2.

Hippo Signaling Pathway Has a Critical Role in Zika Virus Replication and in the Pathogenesis of Neuroinflammation

Zika virus (ZIKV) is a reemerging human pathogen that causes congenital abnormalities, including microcephaly and eye disease. The cellular/molecular basis of ZIKV and host interactions inducing ocular and neuronal pathogenesis are unclear. Herein, we noted that the Hippo/Salvador-Warts-Hippo signaling pathway, which controls organ size through progenitor cell proliferation and differentiation, is dysregulated after ZIKV infection. In human fetal retinal pigment epithelial cells, there is an early induction of transcriptional coactivator, Yes-associated protein (YAP), which is later degraded with a corresponding activation of the TANK binding kinase 1/interferon regulatory factor 3 type I interferon pathway. YAP/transcriptional co-activator with a PDZ-binding domain (TAZ) silencing results in reduced ZIKV replication, indicating a direct role of Hippo pathway in regulating ZIKV infection. Using an in vivo Ifnar1^-/- knockout mouse model, ZIKV infection was found to reduce YAP/TAZ protein levels while increasing phosphorylated YAP Ser127 in the retina and brain. Hippo pathway is activated in major cellular components of the blood-brain barrier, including endothelial cells and astrocytes. In addition, this result suggests AMP-activated protein kinase signaling pathway's role in regulating YAP/TAZ in ZIKV-infected cells. These data demonstrate that ZIKV infection might initiate a cross talk among AMP-activated protein kinase-Hippo-TBK1 pathways, which could regulate antiviral and energy stress responses during oculoneuronal inflammation.

Vertical Transmission of Zika Virus (Flaviviridae, Flavivirus) in Amazonian Aedes aegypti (Diptera: Culicidae) Delays Egg Hatching and Larval Development of Progeny

Zika virus (ZIKV) has emerged as a globally important arbovirus and has been reported from all states of Brazil. The virus is primarily transmitted to humans through the bite of an infective Aedes aegypti (Linnaeus, 1762) or Aedes albopictus (Skuse, 1895). However, it is important to know if ZIKV transmission also occurs from Ae. aegypti through infected eggs to her offspring. Therefore, a ZIKV and dengue virus (DENV) free colony was established from eggs collected in Manaus and maintained until the third-fourth generation in order to conduct ZIKV vertical transmission (VT) experiments which used an infectious bloodmeal as the route of virus exposure. The eggs from ZIKV-infected females were allowed to hatch. The resulting F1 progeny (larvae, pupae, and adults) were quantitative polymerase chain reaction (qPCR) assayed for ZIKV. The viability of ZIKV vertically transmitted to F1 progeny was evaluated by cultivation in C6/36 cells. The effects of ZIKV on immature development of Ae. aegypti was assessed and compared with noninfected mosquitoes. AmazonianAe. aegypti were highly susceptible to ZIKV infection (96.7%), and viable virus passed to their progeny via VT. Moreover, eggs from the ZIKV-infected mosquitoes had a significantly lower hatch rate and the slowest hatching. In addition, the larval development period was slower when compared to noninfected, control mosquitoes. This is the first study to illustrate VT initiated by oral infection of the parental population by using mosquitoes, which originated from the field and a ZIKV strain that is naturally circulating in-country. Additionally, this study suggests that ZIKV present in the Ae. aegypti can modify the mosquito life cycle. The data reported here suggest that VT of ZIKV to progeny from naturally infected females may have a critical epidemiological role in the dissemination and maintenance of the virus circulating in the vector.

Therapeutic Advances Against ZIKV: A Quick Response, a Long Way to Go

Zika virus (ZIKV) is a mosquito-borne flavivirus that spread throughout the American continent in 2015 causing considerable worldwide social and health alarm due to its association with ocular lesions and microcephaly in newborns, and Guillain-Barré syndrome (GBS) cases in adults. Nowadays, no licensed vaccines or antivirals are available against ZIKV, and thus, in this very short time, the scientific community has conducted enormous efforts to develop vaccines and antivirals. So that, different platforms (purified inactivated and live attenuated viruses, DNA and RNA nucleic acid based candidates, virus-like particles, subunit elements, and recombinant viruses) have been evaluated as vaccine candidates. Overall, these vaccines have shown the induction of vigorous humoral and cellular responses, the decrease of viremia and viral RNA levels in natural target organs, the prevention of vertical and sexual transmission, as well as that of ZIKV-associated malformations, and the protection of experimental animal models. Some of these vaccine candidates have already been assayed in clinical trials. Likewise, the search for antivirals have also been the focus of recent investigations, with dozens of compounds tested in cell culture and a few in animal models. Both direct acting antivirals (DAAs), directed to viral structural proteins and enzymes, and host acting antivirals (HAAs), directed to cellular factors affecting all steps of the viral life cycle (binding, entry, fusion, transcription, translation, replication, maturation, and egress), have been evaluated. It is expected that this huge collaborative effort will produce affordable and effective therapeutic and prophylactic tools to combat ZIKV and other related still unknown or nowadays neglected flaviviruses. Here, a comprehensive overview of the advances made in the development of therapeutic measures against ZIKV and the questions that still have to be faced are summarized.

A Novel DT40 Antibody Library for the Generation of Monoclonal Antibodies

Early etiological diagnosis is very important for the control of sudden viral infections, and requires antibodies with both high sensitivity and high specificity. Traditional antibody preparation methods have limitations, such as a long and arduous cycle, complicated operation, and high expenses. A chicken lymphoma cell line, DT40, is known to produce IgM-type antibodies and undergo gene conversion and somatic mutation in the variable region of the immunoglobulin gene during culture. Here, the DT40 cell line was developed to produce antibody libraries and prepare antibody rapidly in vitro. Since hypermutation in DT40 cells was regulated by the activation-induced cytidine deaminase (AID) gene, AID expression needs to be controlled to either fix the Ig sequence by stopping mutation or improve affinity by resuming mutation after the antibodies have been selected. In this study, we generated a novel AID-inducible DT40 cell line (DT40-H7), in which the endogenous AID gene was knocked out using the CRISPR/Cas9 genome editing system, and an inducible AID gene, based on the Tet-Off expression system, was stably transfected. AID expression was controlled in DT40-H7 cells in a simple and efficient manner; gene conversion and point mutations were observed only when AID was expressed. Using the antibody library generated from this cell line, we successfully obtained monoclonal antibodies against the NS1 protein of Zika virus. The DT40-H7 cell line represents a useful tool for the selection and evolution of antibodies and may also be a powerful tool for the rapid selection and generation of diagnostic antibodies for emerging infectious diseases.

Complementary Mechanisms Potentially Involved in the Pathology of Zika Virus

Zika virus (ZIKV) has emerged as a global health threat due to its neuro-teratogenic effect and wide range of transmission routes. Most recently, ZIKV infection has been linked with both autoimmune disorders in adults and neurodevelopmental disorders in newborns. Researchers are exploring potential cellular and molecular mechanisms underlying the neuro-teratogenicity and related consequences by using various in vitro cell culture methods and in vivo animal models. Though some of the putative viral entry receptors have been identified for ZIKV entry into the target cells, the exact mechanism of ZIKV entry or induced pathology are still not clear. Some of the important host cellular pathways including the toll-like receptor (TLR), autophagy, apoptosis and unfolded protein response (UPR) pathways are considered potential mechanism(s) for ZIKV induced neuroinflammation and for neurodevelopmental disorders. Since there is still a dire need for efficient treatment and vaccine to prevent ZIKV mediated disorders, a better understanding of the interaction between virus and host cellular pathways could pave the way for development of targeted therapeutic intervention. In this review, we are focusing on the recent advances and current knowledge regarding the interaction of ZIKV with abovementioned pathways so as to provide basic understanding to execute further research that could aid in the development of novel therapeutic strategy.

Host-Directed Antivirals: A Realistic Alternative to Fight Zika Virus

Zika virus (ZIKV), a mosquito-borne flavivirus, was an almost neglected pathogen until its introduction in the Americas in 2015, where it has been responsible for a threat to global health, causing a great social and sanitary alarm due to its increased virulence, rapid spread, and an association with severe neurological and ophthalmological complications. Currently, no specific antiviral therapy against ZIKV is available, and treatments are palliative and mainly directed toward the relief of symptoms, such as fever and rash, by administering antipyretics, anti-histamines, and fluids for dehydration. Nevertheless, lately, search for antivirals has been a major aim in ZIKV investigations. To do so, screening of libraries from different sources, testing of natural compounds, and repurposing of drugs with known antiviral activity have allowed the identification of several antiviral candidates directed to both viral (structural proteins and enzymes) and cellular elements. Here, we present an updated review of current knowledge about anti-ZIKV strategies, focusing on host-directed antivirals as a realistic alternative to combat ZIKV infection.

In situ immune response and mechanisms of cell damage in central nervous system of fatal cases microcephaly by Zika virus

Zika virus (ZIKV) has recently caused a pandemic disease, and many cases of ZIKV infection in pregnant women resulted in abortion, stillbirth, deaths and congenital defects including microcephaly, which now has been proposed as ZIKV congenital syndrome. This study aimed to investigate the in situ immune response profile and mechanisms of neuronal cell damage in fatal Zika microcephaly cases. Brain tissue samples were collected from 15 cases, including 10 microcephalic ZIKV-positive neonates with fatal outcome and five neonatal control flavivirus-negative neonates that died due to other causes, but with preserved central nervous system (CNS) architecture. In microcephaly cases, the histopathological features of the tissue samples were characterized in three CNS areas (meninges, perivascular space, and parenchyma). The changes found were mainly calcification, necrosis, neuronophagy, gliosis, microglial nodules, and inflammatory infiltration of mononuclear cells. The in situ immune response against ZIKV in the CNS of newborns is complex. Despite the predominant expression of Th2 cytokines, other cytokines such as Th1, Th17, Treg, Th9, and Th22 are involved to a lesser extent, but are still likely to participate in the immunopathogenic mechanisms of neural disease in fatal cases of microcephaly caused by ZIKV.

In situ immune response and mechanisms of cell damage in central nervous system of fatal cases microcephaly by Zika virus

Zika virus (ZIKV) has recently caused a pandemic disease, and many cases of ZIKV infection in pregnant women resulted in abortion, stillbirth, deaths and congenital defects including microcephaly, which now has been proposed as ZIKV congenital syndrome. This study aimed to investigate the in situ immune response profile and mechanisms of neuronal cell damage in fatal Zika microcephaly cases. Brain tissue samples were collected from 15 cases, including 10 microcephalic ZIKV-positive neonates with fatal outcome and five neonatal control flavivirus-negative neonates that died due to other causes, but with preserved central nervous system (CNS) architecture. In microcephaly cases, the histopathological features of the tissue samples were characterized in three CNS areas (meninges, perivascular space, and parenchyma). The changes found were mainly calcification, necrosis, neuronophagy, gliosis, microglial nodules, and inflammatory infiltration of mononuclear cells. The in situ immune response against ZIKV in the CNS of newborns is complex. Despite the predominant expression of Th2 cytokines, other cytokines such as Th1, Th17, Treg, Th9, and Th22 are involved to a lesser extent, but are still likely to participate in the immunopathogenic mechanisms of neural disease in fatal cases of microcephaly caused by ZIKV.

CD8+ T Cell Immune Response in Immunocompetent Mice during Zika Virus Infection

Zika virus (ZIKV) infection causees neurologic complications, including Guillain-Barré syndrome in adults and central nervous system (CNS) abnormalities in fetuses. We investigated the immune response, especially the CD8⁺ T cell response in C57BL/6 (B6) wild-type (WT) mice, during ZIKV infection. We found that a robust CD8⁺ T cell response was elicited, major histocompatibility complex class I-restricted CD8⁺ T cell epitopes were identified, a tetramer that recognizes ZIKV-specific CD8⁺ T cells was developed, and virus-specific memory CD8⁺ T cells were generated in these mice. The CD8⁺ T cells from these infected mice were functional, as evidenced by the fact that the adoptive transfer of ZIKV-specific CD8⁺ T cells could prevent ZIKV infection in the CNS and was cross protective against dengue virus infection. Our findings provide comprehensive insight into immune responses against ZIKV and further demonstrate that WT mice could be a natural and easy-access model for evaluating immune responses to ZIKV infection.IMPORTANCE ZIKV infection has severe clinical consequences, including Guillain-Barré syndrome in adults, microcephaly, and congenital malformations in fetuses and newborn infants. Therefore, study of the immune response, especially the adaptive immune response to ZIKV infection, is important for understanding diseases caused by ZIKV infection. Here, we characterized the CD8⁺ T cell immune response to ZIKV in a comprehensive manner and identified ZIKV epitopes. Using the identified immunodominant epitopes, we developed a tetramer that recognizes ZIKV-specific CD8⁺ T cells in vivo, which simplified the detection and evaluation of ZIKV-specific immune responses. In addition, the finding that tetramer-positive memory CD8⁺ T cell responses were generated and that CD8⁺ T cells can traffic to a ZIKV-infected brain greatly enhances our understanding of ZIKV infection and provides important insights for ZIKV vaccine design.

Modelling Zika Virus Infection of the Developing Human Brain In Vitro Using Stem Cell Derived Cerebral Organoids

The recent emergence of Zika virus (ZIKV) in susceptible populations has led to an abrupt increase in microcephaly and other neurodevelopmental conditions in newborn infants. While mosquitos are the main route of viral transmission, it has also been shown to spread via sexual contact and vertical mother-to-fetus transmission. In this latter case of transmission, due to the unique viral tropism of ZIKV, the virus is believed to predominantly target the neural progenitor cells (NPCs) of the developing brain. Here a method for modeling ZIKV infection, and the resulting microcephaly, that occur when human cerebral organoids are exposed to live ZIKV is described. The organoids display high levels of virus within their neural progenitor population, and exhibit severe cell death and microcephaly over time. This three-dimensional cerebral organoid model allows researchers to conduct species-matched experiments to observe and potentially intervene with ZIKV infection of the developing human brain. The model provides improved relevance over standard two-dimensional methods, and contains human-specific cellular architecture and protein expression that are not possible in animal models.

The thiopurine nucleoside analogue 6-methylmercaptopurine riboside (6MMPr) effectively blocks Zika virus replication

Since the emergence of Zika virus (ZIKV) in Brazil in 2015, 48 countries and territories in the Americas have confirmed autochthonous cases of disease caused by the virus. ZIKV-associated neurological manifestations and congenital defects make the development of safe and effective antivirals against ZIKV of utmost importance. Here we evaluated the antiviral activity of 6-methylmercaptopurine riboside (6MMPr), a thiopurine nucleoside analogue derived from the prodrug azathioprine, against the epidemic ZIKV strain circulating in Brazil. In all of the assays, an epithelial (Vero) and a human neuronal (SH-SY5Y) cell line were used to evaluate the cytotoxicity and effective concentrations of 6MMPr against ZIKV. Levels of ZIKV-RNA, viral infectious titre and the percentage of infected cells in the presence or absence of 6MMPr were used to determine antiviral efficacy. 6MMPr decreased ZIKV production by >99% in both cell lines in a dose- and time-dependent manner. Interestingly, 6MMPr was 1.6 times less toxic to SH-SY5Y cells compared with Vero cells, presenting a 50% cytotoxic concentrations (CC₅₀) of 460.3 µM and 291 µM, respectively. The selectivity index of 6MMPr for Vero and SH-SY5Y cells was 11.9 and 22.7, respectively, highlighting the safety profile of the drug to neuronal cells. Taken together, these results identify, for the first time, the thiopurine nucleoside analogue 6MMPr as a promising antiviral candidate against ZIKV that warrants further in vivo evaluation.

Zika virus transmission to mouse ear by mosquito bite: a laboratory model that replicates the natural transmission process

Background

Zika disease has transformed into a serious global health problem due to the rapid spread of the arbovirus and alarming severity including congenital complications, microcephaly and Guillain-Barré syndrome. Zika virus (ZIKV) is primarily transmitted to humans through the bite of an infective mosquito, with Aedes aegypti being the main vector.

Methods

We successfully developed a ZIKV experimental transmission model by single infectious Ae. aegypti bite to a laboratory mouse using circulating Brazilian strains of both arbovirus and vector. Mosquitoes were orally infected and single Ae. aegypti were allowed to feed on mouse ears 14 days post-infection. Additionally, salivary gland (SG) homogenates from infected mosquitoes were intrathoracically inoculated into naïve Ae. aegypti. Mosquito and mouse tissue samples were cultured in C6/36 cells and processed by quantitative real-time PCR.

Results

A total of 26 Ae. aegypti were allowed to feed individually on mouse ears. Of these, 17 mosquitoes fed, all to full engorgement. The transmission rate of ZIKV by bite from these engorged mosquitoes to mouse ears was 100%. The amount of virus inoculated into the ears by bites ranged from 2 × 10²–2.1 × 10¹⁰ ZIKV cDNA copies and was positively correlated with ZIKV cDNA quantified from SGs dissected from mosquitoes post-feeding. Replicating ZIKV was confirmed in macerated SGs (2.45 × 10⁷ cDNA copies), mouse ear tissue (1.15 × 10³ cDNA copies, and mosquitoes 14 days post-intrathoracic inoculation (1.49 × 10⁷ cDNA copies) by cytopathic effect in C6/36 cell culture and qPCR.

Conclusions

Our model illustrates successful transmission of ZIKV by an infectious mosquito bite to a live vertebrate host. This approach offers a comprehensive tool for evaluating the development of infection in and transmission from mosquitoes, and the vertebrate-ZIKV interaction and progression of infection following a natural transmission process.

Zika Virus and the Eye

Zika virus (ZIKV), a mosquito-borne flavivirus, is the latest global health concern. Transmission is mainly via Aedes mosquitoes and the infection can be diagnosed on molecular or serologic testings. It typically causes a mild self-remitting illness of low-grade fever, maculopapular rash, and myalgia, but when severe, it is associated with neurological deficits and congenital structural defects. Ocular manifestations are usually mild like nonpurulent conjunctivitis in adults, though it may be linked to uveitis, maculopathy, and hypertensive iridocyclitis. Ocular signs seem to be more significant in congenital ZIKV-macular pigment mottling, neuroretinal atrophy with macular involvement, iris coloboma, and changes in retinal vasculature are noted in infants with infected mothers. Risk factors include ZIKV infection in first trimester and smaller cephalic diameter at birth. Hence, ophthalmic examination in newborns is now recommended. Currently, prevention and active surveillance are integral as there is no known vaccine, and treatment is only symptomatic.

Advances in Developing Therapies to Combat Zika Virus: Current Knowledge and Future Perspectives

Zika virus (ZIKV) remained largely quiescent for nearly six decades after its first appearance in 1947. ZIKV reappeared after 2007, resulting in a declaration of an international "public health emergency" in 2016 by the World Health Organization (WHO). Until this time, ZIKV was considered to induce only mild illness, but it has now been established as the cause of severe clinical manifestations, including fetal anomalies, neurological problems, and autoimmune disorders. Infection during pregnancy can cause congenital brain abnormalities, including microcephaly and neurological degeneration, and in other cases, Guillain-Barré syndrome, making infections with ZIKV a substantial public health concern. Genomic and molecular investigations are underway to investigate ZIKV pathology and its recent enhanced pathogenicity, as well as to design safe and potent vaccines, drugs, and therapeutics. This review describes progress in the design and development of various anti-ZIKV therapeutics, including drugs targeting virus entry into cells and the helicase protein, nucleosides, inhibitors of NS3 protein, small molecules, methyltransferase inhibitors, interferons, repurposed drugs, drugs designed with the aid of computers, neutralizing antibodies, convalescent serum, antibodies that limit antibody-dependent enhancement, and herbal medicines. Additionally, covalent inhibitors of viral protein expression and anti-Toll-like receptor molecules are discussed. To counter ZIKV-associated disease, we need to make rapid progress in developing novel therapies that work effectually to inhibit ZIKV.

A sensitive virus yield assay for evaluation of Antivirals against Zika Virus

Despite the rapid spread of Zika virus (ZIKV) infection and associated neurological complications in the America's, prophylactic or therapeutic countermeasures are not currently available. This is mostly due to the fact that until recently there was no presumed need for medical intervention since there was no association between ZIKV infection and significant human morbidity. Consequently, there are currently no tools due mostly to the lack of sensitive cell based assays amenable for identification of ZIKV inhibitors. To address this unmet need we have developed a cell based virus yield assay suitable for testing antivirals against Zika virus. Using bioinformatics, several isolates of ZIKV from the Americas, Africa, and Asia were analyzed for sequence similarity. The alignment data were then used to design primers targeting a ZIKV genomic region that was highly conserved among all the ZIKV isolates. Subsequently, primers were used in a sensitive, quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay to detect ZIKV RNA. The qRT-PCR assay was found to be highly sensitive (lower limit of detection between-10-100 copies) and reproducible. Evaluation of the primers and probes used for ZIKV against another flavivirus (Dengue virus) demonstrated specificity of detection. To evaluate potential of qRT-PCR assay as an antiviral screening tool against ZIKV, Vero cells pretreated with Type I Interferons (IFN α) were infected with virus, followed by measurement of ZIKV RNA found in the cell culture supernatants using qRT-PCR assay. Dose-dependent antiviral activity of Type I Interferons and mycophenolic acid (MPA) against Zika virus in this cell culture system was confirmed using qRT-PCR. Due to reproducible assay performance, qPCR associated higher sensitivity and short duration of the assay time, this novel cell based assay will be very useful for confirming the activity of antivirals against ZIKV.