Zika virus infection and pregnancy: what we do and do not know

Viral Infections During Pregnancy: The Big Challenge Threatening Maternal and Fetal Health

Viral infections during pregnancy are associated with adverse pregnancy outcomes, including maternal and fetal mortality, pregnancy loss, premature labor, and congenital anomalies. Mammalian gestation encounters an immunological paradox wherein the placenta balances the tolerance of an allogeneic fetus with protection against pathogens. Viruses cannot easily transmit from mother to fetus due to physical and immunological barriers at the maternal-fetal interface posing a restricted threat to the fetus and newborns. Despite this, the unknown strategies utilized by certain viruses could weaken the placental barrier to trigger severe maternal and fetal health issues especially through vertical transmission, which was not fully understood until now. In this review, we summarize diverse aspects of the major viral infections relevant to pregnancy, including the characteristics of pathogenesis, related maternal-fetal complications, and the underlying molecular and cellular mechanisms of vertical transmission. We highlight the fundamental signatures of complex placental defense mechanisms, which will prepare us to fight the next emerging and re-emerging infectious disease in the pregnancy population.

Is the ZIKV Congenital Syndrome and Microcephaly Due to Syndemism with Latent Virus Coinfection?

The emergence of the Zika virus (ZIKV) mirrors its evolutionary nature and, thus, its ability to grow in diversity or complexity (i.e., related to genome, host response, environment changes, tropism, and pathogenicity), leading to it recently joining the circle of closed congenital pathogens. The causal relation of ZIKV to microcephaly is still a much-debated issue. The identification of outbreak foci being in certain endemic urban areas characterized by a high-density population emphasizes that mixed infections might spearhead the recent appearance of a wide range of diseases that were initially attributed to ZIKV. Globally, such coinfections may have both positive and negative effects on viral replication, tropism, host response, and the viral genome. In other words, the possibility of coinfection may necessitate revisiting what is considered to be known regarding the pathogenesis and epidemiology of ZIKV diseases. ZIKV viral coinfections are already being reported with other arboviruses (e.g., chikungunya virus (CHIKV) and dengue virus (DENV)) as well as congenital pathogens (e.g., human immunodeficiency virus (HIV) and cytomegalovirus (HCMV)). However, descriptions of human latent viruses and their impacts on ZIKV disease outcomes in hosts are currently lacking. This review proposes to select some interesting human latent viruses (i.e., herpes simplex virus 2 (HSV-2), Epstein-Barr virus (EBV), human herpesvirus 6 (HHV-6), human parvovirus B19 (B19V), and human papillomavirus (HPV)), whose virological features and co-exposition with ZIKV may provide evidence of the syndemism process, shedding some light on the emergence of the ZIKV-induced global congenital syndrome in South America.

Evaluation of the frequency of neuroimaging findings in congenital infection by Zika virus and differences between computed tomography and magnetic resonance imaging in the detection of alterations

INTRODUCTION

Congenital infection by the Zika virus (ZIKV) is responsible for severe abnormalities in the development of the central nervous system. The aim of this study was to evaluate and compare the ability of computed tomography (CT) and magnetic resonance (MR) to detect patterns of involvement of the central nervous system in congenital ZIKV syndrome.

METHODS

We retrospectively analyzed CT and MR images from 34 patients with congenital ZIKV syndrome and evaluated the differences between the two methods in detecting alterations.

RESULTS

The predominant radiographic finding was a simplified gyral pattern, present in 97% of cases. The second most common finding was the presence of calcifications (94.1%), followed by ventriculomegaly (85.3%), dysgenesis of the corpus callosum (85.3%), craniofacial disproportion and redundant scalp (79.4%), complete opercular opening (79.4%), occipital prominence (44.1%), cerebellar hypoplasia (14.7%), and pontine hypoplasia (11.8%). The gyral pattern was extensively simplified in most cases, and calcifications were located predominantly at the cortical-subcortical junction. CT was able to better identify calcifications (94.1% × 88.2%), while MRI presented better spatial resolution for the characterization of gyral pattern (97% × 94.1%) and corpus callosum dysgenesis (85.3% × 79.4%).

CONCLUSIONS

Although congenital ZIKV syndrome does not present pathognomonic neuroimaging findings, some aspects, such as calcifications at the cortical-subcortical junction, especially when associated with compatible clinical and laboratory findings, are suggestive of intrauterine ZIKV infection.

Reduced Midbrain Dopamine Neuron Number in the Adult Non-human Primate Brain after Fetal Radiation Exposure

Early gestation is a neurodevelopmental period that is especially vulnerable to environmental insult and one in which neurogenesis features prominently. Prenatal perturbation during early gestation has been linked to neuropsychiatric illnesses such as autism and schizophrenia, and severe environmental insult during this period can result in profound mental impairment. Midbrain dopamine neurons are generated during early gestation and play a key role in the motor, cognitive and reward circuitries implicated in neuropsychiatric disease and addiction. This study examined the impact of curtailing neurogenesis in early gestation on neuron number in the midbrain dopamine group, i.e., the substantia nigra and contiguous ventral tegmental area. Rhesus macaque monkeys were exposed in utero on embryonic days 39-41 to x-irradiation (3-4 exposures of 50 cGy over 3-7 days totalling <200 cGy) and allowed to mature to full adulthood. Stereologic cell counts of tyrosine hydroxylase-positive neurons in the midbrain dopamine group were performed in adult monkeys, as were measurements of somal size. Mean total neuron number in the irradiated monkeys was significantly reduced on average by 33% compared to that of the control group. Somal size did not differ between the groups, suggesting that the integrity of survivor populations was not impacted. Reduced midbrain dopamine neuron number in fetally irradiated, adult monkeys indicates that radiation exposure during the critical period of neurogenesis results in an enduring reduction of this population and underscores the susceptibility of early neurodevelopmental processes to irreversible damage from environmental exposures.

Performance of Zika Assays in the Context of Toxoplasma gondii, Parvovirus B19, Rubella Virus, and Cytomegalovirus (TORCH) Diagnostic Assays

Infections during pregnancy that may cause congenital abnormalities have been recognized for decades, but their diagnosis is challenging. This was again illustrated with the emergence of Zika virus (ZIKV), highlighting the inherent difficulties in estimating the extent of pre- and postnatal ZIKV complications because of the difficulties in establishing definitive diagnoses. We reviewed the epidemiology, infection kinetics, and diagnostic methods used for Toxoplasma gondii, parvovirus B19, rubella virus, and cytomegalovirus (TORCH) infections and compared the results with current knowledge of ZIKV diagnostic assays to provide a basis for the inclusion of ZIKV in the TORCH complex evaluations. Similarities between TORCH pathogens and ZIKV support inclusion of ZIKV as an emerging TORCH infection. Our review evaluates the diagnostic performance of various TORCH diagnostic assays for maternal screening, fetal screening, and neonatal screening. We show that the sensitivity, specificity, and positive and negative predictive value of TORCH complex pathogens are widely variable, stressing the importance of confirmatory testing and the need for novel techniques for earlier and accurate diagnosis of maternal and congenital infections. In this context it is also important to acknowledge different needs and access to care for different geographic and resource settings.

Clinical findings in congenital infection by Zika virus: a retrospective study in a reference hospital in Central-West Brazil

Background

An increased number of congenital Zika virus infections with neurological and musculoskeletal malformations have been diagnosed worldwide, however, there are still several gaps in the knowledge about this infection, its associated mechanism, timing of transmission, and description of throughout findings of signs and symptoms, which is described in this paper. The purpose of this study is to describe aspects of congenital Zika syndrome (CZS) beyond the central nervous system comprising detailed delineation of all the other clinical findings.

Methods

A retrospective research developed using electronic medical records. We analyzed the files of 69 children with an initial diagnosis of microcephaly by Zika vírus who were born in 2015, 2016 and 2017, treated during the period from 2016 to 2017.

Results

The newborns presented several neurological and musculoskeletal malformations, eye damage, hearing impairment and other malformations.

Conclusions

The present study has significant impact for health care teams following lactents with Congenital Zika Syndrome.

Zika Virus Potentiates the Development of Neurological Defects and Microcephaly: Challenges and Control Strategies

Since the beginning of the Zika Virus (ZIKV) epidemic, thousands of cases presenting ZIKV symptoms were recorded in Brazil, Colombia (South America), French Polynesia and other countries of Central and North America. In Brazil, during ZIKV outbreak thousands of microcephaly cases occurred that caused a state of urgency among scientists and researchers to confirm the suspected association between ZIKV infection and microcephaly. In this review article we comprehensively studied scientific literature to analyze ZIKV relationship with microcephaly, recent experimental studies, challenge and shortcomings in previously published reports to know about the current status of this association. The evidences supporting the association of ZIKV infection with congenital microcephaly and fetal brain tissue damage is rapidly increasing, and supplying recent information about pathology, clinical medicine, epidemiology, mechanism and experimental studies. However, serious attention is required toward ZIKV vaccine development, standardization of anthropometric techniques, centralization of data, and advance research to clearly understand the mechanism of ZIKV infection causing microcephaly.

Identifying Windows of Susceptibility by Temporal Gene Analysis

Increased understanding of developmental disorders of the brain has shown that genetic mutations, environmental toxins and biological insults typically act during developmental windows of susceptibility. Identifying these vulnerable periods is a necessary and vital step for safeguarding women and their fetuses against disease causing agents during pregnancy and for developing timely interventions and treatments for neurodevelopmental disorders. We analyzed developmental time-course gene expression data derived from human pluripotent stem cells, with disease association, pathway, and protein interaction databases to identify windows of disease susceptibility during development and the time periods for productive interventions. The results are displayed as interactive Susceptibility Windows Ontological Transcriptome (SWOT) Clocks illustrating disease susceptibility over developmental time. Using this method, we determine the likely windows of susceptibility for multiple neurological disorders using known disease associated genes and genes derived from RNA-sequencing studies including autism spectrum disorder, schizophrenia, and Zika virus induced microcephaly. SWOT clocks provide a valuable tool for integrating data from multiple databases in a developmental context with data generated from next-generation sequencing to help identify windows of susceptibility.

Sources affecting knowledge and behavior responses to the Zika virus in US households with current pregnancy, intended pregnancy and a high probability of unintended pregnancy

Background

This study examined the influences of information sources on Zika-relevant knowledge and behaviors in US households containing members who are pregnant, intend to become pregnant, or have a higher probability of unintended pregnancy in Zika-affected regions (i.e. respondents who are younger, are black, have less education, are unmarried, and reside in the southern USA).

Methods

Over 32 000 US adults completed a survey measuring Zika-relevant knowledge and behaviors along with information sources (e.g. discussing Zika with practitioners), general media usage (e.g. TV) and demographic information over 30 weeks.

Results

Respondents in the group with (versus without) either pregnancy or intended pregnancy were more likely to use all information sources, which in turn created differences in knowledge and behavior responses. To gauge information sources in US-South respondents with a high probability of having a household member with unintended pregnancy based on demographics, younger, less-educated, unmarried, black respondents had fewer Zika discussion with practitioners than another group.

Conclusions

Efforts to increase Zika-related knowledge and protective behaviors should target households with members who are pregnant or intending to become pregnant via practitioners, family and friends. Additional efforts should target information channels to reach younger, less educated, unmarried, black respondents, which are at risk for unintended pregnancy.

Maternal Zika Virus Disease Severity, Virus Load, Prior Dengue Antibodies, and Their Relationship to Birth Outcomes

Background

Congenital Zika virus (ZIKV) syndrome is a newly identified condition resulting from infection during pregnancy. We analyzed outcome data from a mother-infant cohort in Rio de Janeiro in order to assess whether clinical severity of maternal ZIKV infection was associated with maternal virus load, prior dengue antibodies, or abnormal pregnancy/infant outcomes.

Methods

A clinical severity assessment tool was developed based on duration of fever, severity of rash, multisystem involvement, and duration of symptoms during ZIKV infection. ZIKV-RNA load was quantified by polymerase chain reaction (PCR) cycles in blood/ urine. Dengue immunoglobulin G (IgG) antibodies were measured at baseline. Adverse outcomes were defined as fetal loss or a live infant with grossly abnormal clinical or brain imaging findings. Regression models were used to study potential associations.

Results

131 ZIKV-PCR positive pregnant women were scored for clinical disease severity, 6 (4.6%) had mild disease, 98 (74.8%) had moderate disease, and 27 (20.6%) severe manifestations of ZIKV infection. There were 58 (46.4%) abnormal outcomes with 9 fetal losses (7.2%) in 125 pregnancies. No associations were found between: disease severity and abnormal outcomes (P = .961; odds ratio [OR]: 1.00; 95% confidence interval [CI]: 0.796-1.270); disease severity and viral load (P = .994); viral load and adverse outcomes (P = .667; OR: 1.02; 95% CI: 0.922-1.135); or existence of prior dengue antibodies (88% subjects) with severity score, ZIKV-RNA load or adverse outcomes (P = .667; OR: 0.78; 95% CI: 0.255-2.397).

Conclusions

Congenital ZIKV syndrome does not appear to be associated with maternal disease severity, ZIKV-RNA load at time of infection or existence of prior dengue antibodies.

Zika virus like particles elicit protective antibodies in mice

Mosquito-borne Zika virus (ZIKV) typically causes a mild and self-limiting illness known as Zika fever. Since its recent emergence in 2014 in the American continent, ZIKV infection during pregnancy has been closely associated with a wide range of congenital abnormalities. To date, no vaccines or antivirals are publicly available. We developed Zika virus-like particles (VLPs) and evaluated their immunogenicity and protective efficacy in mouse models. ZIKV VLPs (ZIKVLPs) formulated with alum were injected into 6-8-week-old interferon deficient AG129 mice as well as wild type BALB/c mice. Control mice received PBS/alum. Animals were challenged with 200 PFU (>1000 AG129 LD50s) of ZIKV strain H/PF/2013. All vaccinated mice survived with no morbidity or weight loss while control animals either died at 9 days post challenge (AG129) or had increased viremia (BALB/c). Neutralizing antibodies were observed in all ZIKVLP vaccinated mice. The role of neutralizing antibodies in protecting mice was demonstrated by passive transfer. Our findings demonstrate the protective efficacy of the ZIKVLP vaccine and highlight the important role that neutralizing antibodies play in protection against ZIKV infection.

Mosquito-borne Zika virus (ZIKV) typically causes a mild and self-limiting illness known as Zika fever. During the recent outbreak in South America, ZIKV infection during pregnancy was associated with severe congenital abnormalities. We developed a vaccine against ZIKV utilizing virus-like particles (VLPs). VLPs are structurally similar to viruses, but are not infectious. We injected mutant mice capable of succumbing to ZIKV infection with these VLPs. Mice vaccinated with VLPs survived infection, while negative control mice died. These studies are important because ZIKVLP based vaccines could be tested in humans as a prophylactic candidate with minimal safety concerns able to protect unborn babies whose mothers become infected with Zika virus during pregnancy.

Imaging findings in congenital Zika virus infection syndrome: an update

BACKGROUND

Zika virus (ZIKV) is a neurotropic and neurotoxic RNA Flavivirus prompt to cause severe fetal brain dysmorphisms during pregnancy, a period of rapid and critical central nervous system development. A wide range of clinico-radiological findings of congenital ZIKV infections were reported in the literature, such as microcephaly, overlapping sutures, cortical migrational and corpus callosum abnormalities, intracranial calcifications, ventriculomegaly, brain stem and cerebellar malformations, spinal cord involvement, and joint contractures. ZIKV is also related to other severe neurological manifestations in grown-up individuals such as Guillain-Barré syndrome and encephalomyelitis.

PURPOSE

Our purpose is to review the radiological central nervous system abnormalities of congenital ZIKV infection syndrome on different imaging modalities.

Congenital Zika syndrome and neuroimaging findings: what do we know so far?

Although infection with the Zika virus was first recognized in 1942, it received little attention until 2007, when a true pandemic spread throughout Africa, Asia, and the Americas. Since then, numerous forms of central nervous system involvement have been described, mainly malformations related to congenital infection. Although the neuroimaging findings in congenital Zika syndrome are not pathognomonic, many are quite suggestive of the diagnosis, and radiologists should be prepared to interpret such findings accordingly. The objective of this article is to review the computed tomography and magnetic resonance imaging findings in congenital Zika syndrome.

Zika virus tropism and interactions in myelinating neural cell cultures: CNS cells and myelin are preferentially affected

The recent global outbreak of Zika virus (ZIKV) infection has been linked to severe neurological disorders affecting the peripheral and central nervous systems (PNS and CNS, respectively). The pathobiology underlying these diverse clinical phenotypes are the subject of intense research; however, even the principal neural cell types vulnerable to productive Zika infection remain poorly characterised. Here we used CNS and PNS myelinating cultures from wild type and Ifnar1 knockout mice to examine neuronal and glial tropism and short-term consequences of direct infection with a Brazilian variant of ZIKV. Cell cultures were infected pre- or post-myelination for various intervals, then stained with cell-type and ZIKV-specific antibodies. In bypassing systemic immunity using ex vivo culture, and the type I interferon response in Ifnar1 deficient cells, we were able to evaluate the intrinsic infectivity of neural cells. Through systematic quantification of ZIKV infected cells in myelinating cultures, we found that ZIKV infection is enhanced in the absence of the type I interferon responses and that CNS cells are considerably more susceptible to infection than PNS cells. In particular, we demonstrate that CNS axons and myelinating oligodendrocytes are especially vulnerable to injury. These results have implications for understanding the pathobiology of neurological symptoms associated with ZIKV infection. Furthermore, we provide a quantifiable ex vivo infection model that can be used for fundamental and therapeutic studies on viral neuroinvasion and its consequences.

Emerging Infectious Diseases and Blood Safety: Modeling the Transfusion-Transmission Risk

While the transfusion-transmission (TT) risk associated with the major transfusion-relevant viruses such as HIV is now very low, during the last 20 years there has been a growing awareness of the threat to blood safety from emerging infectious diseases, a number of which are known to be, or are potentially, transfusion transmissible. Two published models for estimating the transfusion-transmission risk from EIDs, referred to as the Biggerstaff-Petersen model and the European Upfront Risk Assessment Tool (EUFRAT), respectively, have been applied to several EIDs in outbreak situations. We describe and compare the methodological principles of both models, highlighting their similarities and differences. We also discuss the appropriateness of comparing results from the two models. Quantitating the TT risk of EIDs can inform decisions about risk mitigation strategies and their cost-effectiveness. Finally, we present a qualitative risk assessment for Zika virus (ZIKV), an EID agent that has caused several outbreaks since 2007. In the latest and largest ever outbreak, several probable cases of transfusion-transmission ZIKV have been reported, indicating that it is transfusion-transmissible and therefore a risk to blood safety. We discuss why quantitative modeling the TT risk of ZIKV is currently problematic.

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During the last 20 years there has been a growing awareness of the threat to blood safety from emerging infectious diseases (EIDs), a number of which are known to be, or are potentially, transfusion-transmissible.

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The transfusion-transmission risk of EID agents can be estimated by risk modeling which can form an important part of risk assessments and inform decisions regarding risk mitigation strategies.

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We describe and compare the methodological principles of two published risk models for estimating the transfusion transmission risk of EIDs.

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We use Zika virus as a case study to demonstrate that reliable risk modeling for EID agents can be problematic due to the uncertainty of the input parameters.

Emerging Zoonotic and Vector-Borne Viral Diseases

Many vector-borne and zoonotic diseases are considered to be emerging; since they are either newly reported to cause human disease, or are causing disease in geographical locations or species not previously documented. In the past 15 years, significant outbreaks of Severe Acute Respiratory Syndrome (or SARS) and Middle Eastern Respiratory Syndrome (or MERS), Nipah and Hendra, Ebola virus disease and Zika fever and others have been reported. In this chapter the clinical characteristics, epidemiological aspects, treatment and prevention and information related to the laboratory investigation of important zoonotic and vector-borne diseases that have emerged in the past 10 years, and how this affects children, will be discussed. Furthermore rabies, considered a neglected viral disease with the majority of victims in Africa being children, will also be addressed.