Society for Maternal-Fetal Medicine (SMFM) Publications Committee. Ultrasound screening for fetal microcephaly following Zika virus exposure

Selection of Standards for Sonographic Fetal Head Circumference by Use of z-Scores

OBJECTIVE

This study aimed to evaluate which of five established norms should be used for sonographic assessment of fetal head circumference (HC).

STUDY DESIGN

Cross-sectional study using pooled data from four maternal-fetal medicine practices. Inclusion criteria were singleton fetus, gestational age 220/7 to 396/7 weeks, biometry measured, and fetal cardiac activity present. Five norms of HC were studied: Jeanty et al, Hadlock et al, the INTERGROWTH-21st Project (IG-21st), the World Health Organization Fetal Growth Curves (WHO), and the National Institutes of Child Health and Human Development Fetal Growth Studies unified standard (NICHD-U). The fit of our HC measurements to each norm was assessed by these criteria: mean z-score close to 0, standard deviation (SD) of z close to 1, low Kolmogorov-Smirnov D-statistic, high Youden J-statistic, close to 10% of exams >90th percentile, close to 10% of exams <10th percentile, and close to 2.28% of exams >2 SD below the mean.

RESULTS

In 23,565 ultrasound exams, our HC measurements had the best fit to the WHO standard (mean z-score 0.10, SD of z = 1.01, D-statistic <0.01, J-statistic 0.83-0.94). The SD of the Jeanty reference was much larger than all the other norms and our measurements, resulting in underdiagnosis of abnormal HC. The means of the IG-21st and NICHD-U standards were smaller than the other norms and our measurements, resulting in underdiagnosis of small HC. The means of the Hadlock reference were larger than all the other norms and our measurements, resulting in overdiagnosis of small HC. Restricting the analysis to a low-risk subgroup of 4,423 exams without risk factors for large- or small-for-gestational age produced similar results.

CONCLUSION

The WHO standard is likely best for diagnosis of abnormal HC. The Jeanty (Chervenak) reference suggested by the Society for Maternal-Fetal Medicine had poor sensitivity for microcephaly screening.

KEY POINTS

· There are >30 norms for fetal HC.. · It is unknown which norm should be used.. · The WHO standard fits our data best.. · The Chervenak reference is not sensitive for microcephaly..

Prenatal counseling of an isolated fetal small head circumference during the second trimester expert ultrasound examination

OBJECTIVE

To evaluate perinatal and postnatal outcomes of fetuses with an isolated small head circumference (HC) on expert ultrasound examination in the second trimester for further recommendations in prenatal care.

STUDY DESIGN

In a retrospective cohort we included singleton-pregnancies with a fetal HC > -3.0 SD and ≤ -1.64 SD determined on expert ultrasound examination between 18 and 24 weeks of gestational age. Three subgroups were determined: "isolated small HC (ISHC)", "small HC plus abdominal circumference (AC) ≤ p10 (SHC+)" and "small HC plus AC ≤ p10 and Doppler abnormalities (SHC + D)". After ultrasound examination, genetic testing was sometimes offered and postnatally genetic tests were performed on indication.

RESULTS

We included 252 pregnancies: 109 ISHC, 104 SHC+, and 39 SHC + D. In the ISHC and SHC+ subgroup, 96 % of the fetuses were born alive and did not die neonatal. In the SH + D group this was only 38 %. In the SHC+ subgroup, less fetuses were delivered vaginal (non-instrumental) compared to the ISHC subgroup (61 % vs. 73 %, p < 0.01). In the ISHC and SHC+ subgroup s some fetuses were diagnosed with congenital defects (4 % vs. 10 %, p = 0.08) and with a genetic anomaly (6.4 % vs. 7.7 %, p = 0.13) after 24 weeks or postnatally. In SHC + D subgroups 5 % presented with congenital defects and 2.6 % with a genetic anomaly.

CONCLUSION

We conclude that fetuses with a small HC without structural anomalies on second trimester expert ultrasound require follow-up and special medical attention. We recommend differentiating between ISHC, SHC+, and SHC + D for prenatal counseling. Genetic testing and referral to a clinical geneticist should be considered.

Clinical Practice Guidelines and Recommendations by the World Association of Perinatal Medicine and Perinatal Medicine Foundation: Reporting Suspected Findings from Fetal Central Nervous System Examination

These guidelines follow the mission of the World Association of Perinatal Medicine, in collaboration with the Perinatal Medicine Foundation, which brings together groups and individuals worldwide, with the aim to improve prenatal detection of central nervous system anomalies and the appropriate referral of pregnancies with suspected fetal anomalies. In addition, this document provides further guidance for healthcare practitioners with the goal of standardizing the description of ultrasonographic abnormal findings.

Prenatal evaluation of genetic variants in fetuses with small head circumference: A single-center retrospective study

OBJECTIVES

To comprehensively evaluate the contributions of numerical chromosomal abnormality, copy number variant (CNV), and sequence variant (SV) to fetuses with small head circumference in a Chinese cohort using chromosome microarray analysis and whole exome sequencing.

METHODS

A total of 157 fetuses with small heads defined as head circumference < - 2 standard deviation (SD) were recruited between October 2014 and March 2023. We used the ultrasonic measurement parameter Z-score to define small head as possible microcephaly (3 < Z ≤ -2), microcephaly (-5 < Z ≤ -3), or pathologic microcephaly (Z ≤ -5). Ultrasound findings and genetic results were analyzed.

RESULTS

The overall diagnostic yield of chromosomal abnormalities by microarray analysis was 13 %. Whole exome sequencing revealed eight novel variants and two interesting candidate genes and provided a 25.4 % incremental yield compared with microarray analysis. Of the detected SVs, 56 % were de novo and the most common inheritance pattern was autosomal dominant inheritance presented in 11/16 fetuses. Compared with isolated small heads, non-isolated small heads had a significantly higher detection rate of chromosomal abnormalities (16 % vs. 3.0 %, P = 0.049) but not SVs (24 % vs. 5.5 %, P = 0.126). Subgroup analysis showed that intracranial anomalies had a similar high detection rate of SVs in fetuses with all small heads subgroups while no chromosomal abnormalities and causative SVs were found in fetuses with isolated possible microcephaly.

CONCLUSIONS

Ultrasound findings of small fetal head circumference < 3 SD below the mean, especially those with intracranial structural abnormalities, indicate the need for genetic counseling. Genetic variants, mainly copy number variants and SV, may be responsible for the substantial proportion of small fetal head circumference, while most are de novo. Whole exome sequencing and microarray analysis are effective diagnostic approaches for this population.

Prenatal diagnosis of microcephaly through combined MRI and ultrasonography: Analysis of a case series

INTRODUCTION

Intrauterine microcephaly is a complex and lifelong condition that poses significant ethical challenges for clinicians and parents. The prognosis of microcephaly is highly variable and depends on the underlying cause and severity. In addition, microcephaly is often associated with various comorbidities, including intellectual disability, developmental delay, and epilepsy. Ultrasonography (US) is currently the most commonly used imaging modality for detecting microcephaly in the second trimester of pregnancy. However, antenatal brain magnetic resonance imaging (MRI) is increasingly being used as a more sensitive tool to identify structural abnormalities that may suggest a specific diagnosis. In this study, we report a case series of microcephaly diagnosed through the combination of MRI and US.

PATIENT CONCERNS

How to utilize a combination of MRI and US to screen for fetal microcephaly.

DIAGNOSIS

Based on the results of US and MRI examinations, patient 1 was found to have other craniocerebral malformations, patient 2 demonstrated macrogyria, and patient 3 exhibited skull irregularities.

INTERVENTIONS

The pregnancies of all 3 patients were terminated through the induction of labor by injecting Rivanol into the amniotic cavity.

OUTCOMES

The 3 patients were discharged after a period of observation.

CONCLUSION

US is an important tool for diagnosing fetal microcephaly. However, MRI can overcome the limitations of US and detect additional brain structural abnormalities, thereby providing more specific and valuable prenatal diagnostic information. Therefore, combining MRI and US has significant diagnostic value for fetal microcephaly.

A Case of Ultrasound Suspected Microcephaly With a Normal Head Circumference at Birth

A 25-year-old first-time mother from Nepal had a well-progressing spontaneous pregnancy. However, from the 37th week, her baby's biparietal diameter (BPD) stopped growing at around 83 mm. At 40 weeks, measurements suggested possible microcephaly and fetal growth failure but no other abnormalities. No travel, infections, or cytomegalovirus were identified prenatally. By 41 weeks, the BPD and head circumference (HC) decreased further, while the estimated fetal birth weight (EFBW) slightly increased. The baby girl was born at 41 weeks and 1 day with a low birth weight but a normal head circumference. Postnatal checks showed no abnormalities, and she was discharged with normal growth at 10 days old.

Fetal Brain Development: Regulating Processes and Related Malformations

This paper describes the contemporary state of knowledge regarding processes that regulate normal development of the embryonic–fetal central nervous system (CNS). The processes are described according to the developmental timetable: dorsal induction, ventral induction, neurogenesis, neuronal migration, post-migration neuronal development, and cortical organization. We review the current literature on CNS malformations associated with these regulating processes. We specifically address neural tube defects, holoprosencephaly, malformations of cortical development (including microcephaly, megalencephaly, lissencephaly, cobblestone malformations, gray matter heterotopia, and polymicrogyria), disorders of the corpus callosum, and posterior fossa malformations. Fetal ventriculomegaly, which frequently accompanies these disorders, is also reviewed. Each malformation is described with reference to the etiology, genetic causes, prenatal sonographic imaging, associated anomalies, differential diagnosis, complimentary diagnostic studies, clinical interventions, neurodevelopmental outcome, and life quality.

SFM Interim Practice Recommendations for Zika Virus Infection in Pregnancy

Zika virus (ZIKV) belongs to the family of flaviviruses and is transmitted by mosquitoes of the genus Aedes (A. aegypti and A. albopictus). ZIKV infection in pregnancy can have serious implications on the fetus and the neonate. Vertical transmission to the fetus can occur irrespective of symptomatic or asymptomatic infection in the pregnant woman and the risk can persist throughout pregnancy. The exact frequency of maternal-to-fetal transmission of Zika virus is difficult to determine accurately. The greatest risk of serious fetal sequelae is seen if the infection occurs within the first and second trimester. However, they can also be seen with infections in the third trimester. This document describes the presentation, feto-maternal manifestations, role of prenatal Ultrasound in diagnosis of infection, testing methods and the management in pregnancy and screening in the neonatal period. In the absence of robust evidence as to the definite effects, this document is aimed at providing practice recommendations for the management of this infection.

No 380 - Évaluation et prise en charge de la microcéphalie détectée avant la naissance

OBJECTIF

Informer les fournisseurs canadiens de soins de santé périnatale des critères diagnostiques de la microcéphalie fœtale et fournir l'information sur les analyses pertinentes, le pronostic, et la prise en charge prénatale et périnatale en lien avec a cette observation prénatale.

DESTINATAIRES

Tous les fournisseurs de soins de maternité (fournisseurs principaux de soins de santé) et de soins de pédiatrie; les conseiller(e)s en génétique; les infirmièr(e)s en soins de maternité; les infirmièr(e)s practicien(ne)s, les administrateur(trice)s provinciaux de soins de maternité; les étudiant(e)s, en médecine; les résident(e)s postdoctoraux et les stagiaires (fellows). RéSULTATS: Fournir de meilleurs conseils et une prise en charge clinique adéquate aux femmes et aux familles qui ont reçu un diagnostic prénatal de microcéphalie fœtale. DONNéES PROBANTES: La documentation publiée est tirée de recherches effectuées en 2018 dans le moteur PubMed et les bases de données Medline, CINAHL et Cochrane Library au moyen de mots-clés anglais pertinents (prenatal ultrasound, prenatal imaging, fetal, antenatal ou prenatal microcephaly). Des publications supplémentaires ont été sélectionnées à partir des notices bibliographiques de ces articles. PéRIODE DE RECHERCHE: Sept ans (2010-2018); la dernière recherche a été effectuée le 19 avril 2018. L'auteur principal a terminé la validation des articles. AVANTAGES, PRéJUDICES ET COûTS: Le présent document renseigne les lecteurs au sujet (1) des critères diagnostiques de la microcéphalie fœtale, (2) de ses étiologies potentielles et (3) des analyses et options de prise en charge avant et après la naissance. Il propose une méthode fondée sur des données probantes pour établir le diagnostic et déterminer la prise en charge de la microcéphalie détectée avant la naissance. Ces recommandations sont fondées sur l'opinion d'experts, mais n'ont pas fait l'objet d'une évaluation économique de la santé. Une mise en œuvre aux échelles locale ou provinciale sera requise. Les auteurs reconnaissent que l'accès aux services et ressources mentionnés varie au Canada. Par conséquent, ces recommandations ont été formulées dans la perspective de promouvoir l'accès et de fournir une orientation pour toutes les provinces et tous les territoires du pays. CRITèRES: La solidité des données probantes indiquées s'appuie sur les critères décrits dans le rapport du Groupe d'étude canadien sur les soins de santé préventifs. RECOMMANDATIONS.

No. 380-Investigation and Management of Prenatally Identified Microcephaly

OBJECTIVE

To update Canadian maternity care and reproductive health care providers on the diagnostic criteria of fetal microcephaly and provide information on the relevant investigations, prognosis, and pre- and perinatal management of this prenatal finding.

INTENDED USERS

All maternity care (most responsible health provider [MRHP]) and pediatric providers; genetic counsellors; maternity nurses; nurse practitioners; provincial maternity care administrators; medical students; postgraduate residents, and fellows.

OUTCOMES

To provide better counselling and appropriate clinical management to women and families who have received a prenatal diagnosis of fetal microcephaly.

EVIDENCE

Published literature was retrieved through searches of PubMed or Medline, CINAHL, and The Cochrane Library in 2018, using appropriate key words (prenatal ultrasound, prenatal imaging, fetal, antenatal, or prenatal microcephaly). Additional publications were identified from the bibliographies of these articles.

SEARCH PERIOD

Seven years (2010-2018); completed final search April 19, 2018. The primary author completed validation of the articles.

BENEFITS, HARMS, AND COSTS

This document educates readers about (1) the diagnostic criteria for fetal microcephaly, (2) its potential etiologies, (3) investigation and management options both pre- and postnatally. It proposes an evidence-based approach to the diagnosis and management of prenatally detected microcephaly. These recommendations are based on expert opinion and have not been subjected to a health economics assessment. Local or provincial implementation will be required. The authors recognize that there is variability across Canada in access to the cited services and resources. As such, these recommendations were developed in an attempt to promote access and to provide guidance for all provinces and territories across the country.

VALUES

The quality of evidence was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care.

RECOMMENDATIONS

Ultrasound prediction of Zika virus-associated congenital injury using the profile of fetal growth

Zika virus (ZIKV) is a mosquito-transmitted flavivirus, recently linked to microcephaly and central nervous system anomalies following infection in pregnancy. Striking findings of disproportionate growth with a smaller than expected head relative to body length have been observed more commonly among fetuses with exposure to ZIKV in utero compared to pregnancies without ZIKV infection regardless of other signs of congenital infection including microcephaly. This study's objective was to determine the diagnostic accuracy of femur-sparing profile of intrauterine growth restriction for the identification of ZIKV-associated congenital injuries on postnatal testing. A retrospective cohort study of pregnant women with possible or confirmed ZIKV infection between January 1, 2016 and December 31, 2017 were included. Subjects were excluded if no prenatal ultrasound was available. A femur-sparing profile of growth restriction determined using INTERGROWTH-21st sonographic standard for head circumference to femur length (HC: FL). Congenital injuries were determined postnatally by imaging, comprehensive eye exam and standard newborn hearing screen. A total of 111 pregnant women diagnosed with ZIKV infection underwent fetal ultrasound and 95 neonates had complete postnatal evaluation. Prenatal microcephaly was detected in 5% of fetuses (6/111). Postnatal testing detected ZIKV-associated congenital injuries in 25% of neonates (24/95). A HC: FL Z-score ≤ -1.3 had a 52% specificity (95% CI 41-63%), 82% negative predictive value (NPV, 95% CI 73-88%) for the detection of ZIKV-associated congenital injuries in the neonatal period. A more stringent threshold with a Z-score ≤ -2 was associated with a 90% specificity (95% CI 81-95%), 81% NPV (95% CI 77-85%). Excluding cases of fetal microcephaly, HC: FL (Z-score ≤ -2) demonstrated a similar specificity (89%, 95% CI 81-95%) with superior NPV (87%, 95% CI 84-90%). The sonographic recognition of a normally proportioned fetus may be useful prenatally to exclude a wider spectrum of ZIKV-associated congenital injuries detected postnatally.

Obstetric Ultrasonography to Detect Fetal Abnormalities in a Mouse Model for Zika Virus Infection

In 2015 Zika virus (ZIKV) emerged for the first time in South America. The following ZIKV epidemic resulted in the appearance of a clinical phenotype with microcephaly and other severe malformations in newborns. So far, mechanisms of ZIKV induced damage to the fetus are not completely understood. Previous data suggest that ZIKV may bypass the placenta to reach the fetus. Thus, animal models for ZIKV infection are important to facilitate studies about ZIKV infection during pregnancy. Here, we used ultrasound based imaging (USI) to characterize ZIKV induced pathogenesis in the pregnant Type I interferon receptor-deficient (IFNAR-/-) mouse model. Based on USI we suggest the placenta to be a primary target organ of ZIKV infection enabling ZIKV spreading to the fetus. Moreover, in addition to direct infection of the fetus, the placental ZIKV infection may cause an indirect damage to the fetus through reduced uteroplacental perfusion leading to intrauterine growth retardation (IUGR) and fetal complications as early as embryonic day (ED) 12.5. Our data confirmed the capability of USI to characterize ZIKV induced modifications in mouse fetuses. Data from further studies using USI to monitor ZIKV infections will contribute to a better understanding of ZIKV infection in pregnant IFNAR-/- mice.

Neurologic infections during pregnancy

Neurologic infections during pregnancy represent a significant cause of maternal and fetal morbidity and mortality. Immunologic alterations during pregnancy increase the susceptibility of the premature brain to damage. This chapter summarizes the epidemiology, pathophysiology, and clinical manifestations in the pregnant woman and the infant, and the diagnosis, treatment, and prevention of the major viral, parasitic, and bacterial infections known to affect pregnancy. These organisms include herpes virus, parvovirus, cytomegalovirus, varicella, rubella, Zika virus, toxoplasmosis, malaria, group B streptococcus, listeriosis, syphilis, and tuberculosis. There is an emphasis on the important differences in diagnosis, treatment, and fetal outcome between trimesters. An additional overview is provided on the spectrum of neurologic sequelae of an affected infant, which ranges from developmental delay to hydrocephalus and seizures.

How prenatal head ultrasound reference ranges affect evaluation of possible fetal microcephaly

OBJECTIVES

Different fetal ultrasound (US) nomograms of the head circumference (HC) have been established; however, comparisons between the detection rates of microcephaly among US nomograms are few and inconsistent. We aimed to compare the prenatal diagnostic rate of fetal microcephaly (FM) among four widely used US nomograms of the fetal HC, when applied to the same group of fetuses.

METHODS

We retrospectively identified singleton pregnancies complicated by fetal HC < 5th percentile for gestational age (GA) by US, without other risk factors for FM and with normal fetal brain MRI. Raw values of HC by US were converted to z-scores using four nomograms (Chervenak = A, Hadlock = B, Gelber = C, Papageorghiou = D). Z-scores value of the HC were classified as normal, possible normal, or microcephaly if values were >-2, ≤ -2 and >-3, or ≤ -3, respectively and compared among the four nomograms.

RESULTS

Fifty one fetuses at a mean (±SD) GA of 28 (±4) weeks were included. The four nomograms resulted in different z-score values of the fetal HC for the same subject (p < .001) and none of them showed 100% agreement. Reference C and D showed the highest agreement in classifying subjects as normal, possible normal, or with microcephaly (simple Kappa = 0.8915, % agreement = 94.1%), while A and B had the lowest agreement (simple Kappa = 0.0977, % agreement = 51.0%).

CONCLUSIONS

Despite the use of similar prenatal cutoff z-score values of the fetal HC, the four nomograms led to different diagnostic rates of FM. More consistent diagnostic criteria are therefore needed to define FM, especially in the absence of other risk factors for FM and normal fetal brain MRI, since the prenatal diagnosis can affect pregnancy management.

Misclassification in defining and diagnosing microcephaly

BACKGROUND

Several health agencies define microcephaly for surveillance purposes using a single criterion, a percentile or Z-score cut-off for newborn head circumference. This definition, however, conflicts with the reported prevalence of microcephaly even in populations with endemic Zika virus.

OBJECTIVE

We explored possible reasons for this conflict, hypothesising that the definition of microcephaly used in some studies may be incompletely described, lacking the additional clinical criteria that clinicians use to make a formal diagnosis. We also explored the potential for misclassification that can result from differences in these definitions, especially when applying a percentile cut-off definition in the presence of the much lower observed prevalence estimates that we believe to be valid.

METHODS

We conducted simulations under a theoretical bimodal distribution of head circumference. For different definitions of microcephaly, we calculated the sensitivity and specificity using varying cut-offs of head circumference. We then calculated and plotted the positive predictive value for each of these definitions by prevalence of microcephaly.

RESULTS

Simple simulations suggest that if the true prevalence of microcephaly is approximately what is reported in peer-reviewed literature, then relying on cut-off-based definitions may lead to very poor positive predictive value under realistic conditions.

CONCLUSIONS

While a simple head circumference criterion may be used in practice as a screening or surveillance tool, the definition lacks clarification as to what constitutes true pathological microcephaly and may lead to confusion about the true prevalence of microcephaly in Zika-endemic areas, as well as bias in aetiologic studies.

Ultrasound Findings Associated With Antepartum Viral Infection

This article reviews the sonographic manifestations of fetal infection and the role of ultrasound in the evaluation of the fetus at risk for congenital infection. Several ultrasound findings have been associated with in utero fetal infections. For the patient with a known or suspected fetal infection, sonographic identification of characteristic abnormalities can provide useful information for counseling and perinatal management. Demonstration of such findings in the low-risk patient may serve to identify the fetus with a previously unsuspected infection. The clinician should understand the limitations of ultrasound in the prenatal diagnosis of congenital infection and discuss them with the patient.

Effect of head circumference in combination with facial profile line on ultrasonic diagnosis of microcephaly

Objective: Recently, microcephaly has usually been misdiagnosed only by ultrasound via measurement of head circumference (HC). Therefore, the aim of this study is to find another diagnostic index to supplement the original diagnostic method of microcephaly, to improve the detection rate of fetal microcephaly and to reduce the misdiagnosis rate.Methods: We retrospectively analyzed 123 pregnant women from February 2012 to January 2017 with fetal HC less than two standard deviations (SD). The facial profile line (FPL) was determined by ultrasonography. The first method (M1) was only used HC to determine whether the fetus was microcephaly, the second one (M2) was to combine HC and FPL for the diagnosis of microcephaly. Results were classified into five orderly categories by experienced sonographers. ROC curve was drawn to evaluate the diagnostic effect.Results: Among the pregnant women, 14 cases of fetal head circumference were less than 3SD, 109 were -2SD < HC≤ -3SD. A total of 12 cases were confirmed of microcephaly by magnetic resonance imaging (MRI) or postnatal, 10 cases of HC were less than 3SD, 2 were -2SD < HC≤ -3SD. The area under the ROC curve for M1 and M2 were 0.751 and 0.983 respectively.Conclusion: The HC in combination with FPL can be used to evaluate the fetal HC and forehead development quickly, and to improve the sensitivity and specificity of diagnosing fetal microcephaly.

Zika virus and the nonmicrocephalic fetus: why we should still worry

Zika virus is a mosquito-transmitted flavivirus and was first linked to congenital microcephaly caused by a large outbreak in northeastern Brazil. Although the Zika virus epidemic is now in decline, pregnancies in large parts of the Americas remain at risk because of ongoing transmission and the potential for new outbreaks. This review presents why Zika virus is still a complex and worrisome public health problem with an expanding spectrum of birth defects and how Zika virus and related viruses evade the immune response to injure the fetus. Recent reports indicate that the spectrum of fetal brain and other anomalies associated with Zika virus exposure is broader and more complex than microcephaly alone and includes subtle fetal brain and ocular injuries; thus, the ability to prenatally diagnose fetal injury associated with Zika virus infection remains limited. New studies indicate that Zika virus imparts disproportionate effects on fetal growth with an unusual femur-sparing profile, potentially providing a new approach to identify viral injury to the fetus. Studies to determine the limitations of prenatal and postnatal testing for detection of Zika virus-associated birth defects and long-term neurocognitive deficits are needed to better guide women with a possible infectious exposure. It is also imperative that we investigate why the Zika virus is so adept at infecting the placenta and the fetal brain to better predict other viruses with similar capabilities that may give rise to new epidemics. The efficiency with which the Zika virus evades the early immune response to enable infection of the mother, placenta, and fetus is likely critical for understanding why the infection may either be fulminant or limited. Furthermore, studies suggest that several emerging and related viruses may also cause birth defects, including West Nile virus, which is endemic in many parts of the United States. With mosquito-borne diseases increasing worldwide, there remains an urgent need to better understand the pathogenesis of the Zika virus and related viruses to protect pregnancies and child health.

Femur-sparing pattern of abnormal fetal growth in pregnant women from New York City after maternal Zika virus infection

BACKGROUND

Zika virus is a mosquito-transmitted flavivirus, which can induce fetal brain injury and growth restriction following maternal infection during pregnancy. Prenatal diagnosis of Zika virus-associated fetal injury in the absence of microcephaly is challenging due to an incomplete understanding of how maternal Zika virus infection affects fetal growth and the use of different sonographic reference standards around the world. We hypothesized that skeletal growth is unaffected by Zika virus infection and that the femur length can represent an internal standard to detect growth deceleration of the fetal head and/or abdomen by ultrasound.

OBJECTIVE

We sought to determine if maternal Zika virus infection is associated with a femur-sparing pattern of intrauterine growth restriction through analysis of fetal biometric measures and/or body ratios using the 2014 International Fetal and Newborn Growth Consortium for the 21st Century Project and World Health Organization Fetal Growth Chart sonographic references.

STUDY DESIGN

Pregnant women diagnosed with a possible recent Zika virus infection at Columbia University Medical Center after traveling to an endemic area were retrospectively identified and included if a fetal ultrasound was performed. Data were collected regarding Zika virus testing, fetal biometry, pregnancy, and neonatal outcomes. The 2014 International Fetal and Newborn Growth Consortium for the 21st Century Project and World Health Organization Fetal Growth Chart sonographic standards were applied to obtain Z-scores and/or percentiles for fetal head circumference, abdominal circumference, and femur length specific for each gestational week. A novel 2014 International Fetal and Newborn Growth Consortium for the 21st Century Project standard was also developed to generate Z-scores for fetal body ratios with respect to femur length (head circumference:femur length, abdominal circumference:femur length). Data were then grouped within clinically relevant gestational age strata (<24, 24-27 6/7, 28-33 6/7, >34 weeks) to analyze time-dependent effects of Zika virus infection on fetal size. Statistical analysis was performed using Wilcoxon signed-rank test on paired data, comparing either abdominal circumference or head circumference to femur length.

RESULTS

A total of 56 pregnant women were included in the study with laboratory evidence of a confirmed or possible recent Zika virus infection. Based on the Centers for Disease Control and Prevention definition for microcephaly after congenital Zika virus exposure, microcephaly was diagnosed in 5% (3/56) by both the 2014 International Fetal and Newborn Growth Consortium for the 21st Century Project and World Health Organization Fetal Growth Chart standards (head circumference Z-score ≤-2 or ≤2.3%). Using 2014 International Fetal and Newborn Growth Consortium for the 21st Century Project, intrauterine fetal growth restriction was diagnosed in 18% of pregnancies (10/56; abdominal circumference Z-score ≤-1.3, <10%). Analysis of fetal size using the last ultrasound scan for all subjects revealed a significantly abnormal skewing of fetal biometrics with a smaller abdominal circumference vs femur length by either 2014 International Fetal and Newborn Growth Consortium for the 21st Century Project or World Health Organization Fetal Growth Chart (P < .001 for both). A difference in distribution of fetal abdominal circumference compared to femur length was first apparent in the 24-27 6/7 week strata (2014 International Fetal and Newborn Growth Consortium for the 21st Century Project, P = .002; World Health Organization Fetal Growth Chart, P = .001). A significantly smaller head circumference compared to femur length was also observed by 2014 International Fetal and Newborn Growth Consortium for the 21st Century Project as early as the 28-33 6/7 week strata (2014 International Fetal and Newborn Growth Consortium for the 21st Century Project, P = .007). Overall, a femur-sparing pattern of growth restriction was detected in 52% of pregnancies with either head circumference:femur length or abdominal circumference:femur length fetal body ratio <10th percentile (2014 International Fetal and Newborn Growth Consortium for the 21st Century Project Z-score ≤-1.3).

CONCLUSION

An unusual femur-sparing pattern of fetal growth restriction was detected in the majority of fetuses with congenital Zika virus exposure. Fetal body ratios may represent a more sensitive ultrasound biomarker to detect viral injury in nonmicrocephalic fetuses that could impart long-term risk for complications of congenital Zika virus infection.

Detection and Prevention of Perinatal Infection: Cytomegalovirus and Zika Virus

Congenital cytomegalovirus is the most common viral congenital infection, and affects up to 2% of neonates. Significant sequelae may develop after congenital cytomegalovirus, including hearing loss, cognitive defects, seizures, and death. Zika virus is an emerging virus with perinatal implications; a congenital Zika virus syndrome has been identified, and includes findings such as microcephaly, fetal nervous system abnormalities, and neurologic sequelae after birth. Screening, diagnosis, prevention, and treatment of these perinatal infections are reviewed in this article.

Zika virus: a public health perspective

PURPOSE OF REVIEW

Zika virus' impact on pregnancy became widely known in 2015 with a dramatic increase in the number of babies born with microcephaly in Recife, Brazil. A mosquito-borne virus resulting in congenital anomalies is unique, and Zika's ability to cause neurological defects on a large scale was a grim reminder of the Rubella epidemic in the 1950s. Over the past 2 years, studies have provided insight on how Zika virus (ZIKV) infects cells and causes disease, but much remains unknown about the long-term risks of Zika exposure on infant growth and development.

RECENT FINDINGS

The impact of ZIKV on pregnancy extends beyond microcephaly and may only first be identified in infancy. The virus has a long latency in semen and can be transmitted sexually. Transplacental passage occurs through infection of Hofbauer cells in the trophoblast. A major difficulty in management of ZIKV disease is that most infections are asymptomatic and the diagnostic methods are not ideal, making both diagnosis and ascertainment of timing of infection problematic. Several different types of vaccines are in development. Large studies are ongoing to determine the risk and total spectrum of anomalies based on the timing of infection and other environmental exposures.

SUMMARY

This review will summarize the epidemic, what we have learned, what we hope to learn, and current recommendations for care and management.

Clinical assessment and brain findings in a cohort of mothers, fetuses and infants infected with ZIKA virus

BACKGROUND

Congenital Zika virus (ZIKV) infection can be detected in both the presence and absence of microcephaly and manifests as a number of signs and symptoms that are detected clinically and by neuroimaging. However, to date, qualitative and quantitative measures for the purpose of diagnosis and prognosis are limited.

OBJECTIVES

Main objectives of this study conducted on fetuses and infants with confirmed congenital Zika virus infection and detected brain abnormalities were (1) to assess the prevalence of microcephaly and the frequency of the anomalies that include a detailed description based on ultrasound and magnetic resonance imaging in fetuses and ultrasound, magnetic resonance imaging, and computed tomography imaging postnatally, (2) to provide quantitative measures of fetal and infant brain findings by magnetic resonance imaging with the use of volumetric analyses and diffusion-weighted imaging, and (3) to obtain additional information from placental and fetal histopathologic assessments and postnatal clinical evaluations.

STUDY DESIGN

This is a longitudinal cohort study of Zika virus-infected pregnancies from a single institution in Colombia. Clinical and imaging findings of patients with laboratory-confirmed Zika virus infection and fetal brain anomalies were the focus of this study. Patients underwent monthly fetal ultrasound scans, neurosonography, and a fetal magnetic resonance imaging. Postnatally, infant brain assessment was offered by the use of ultrasound imaging, magnetic resonance imaging, and/or computed tomography. Fetal head circumference measurements were compared with different reference ranges with <2 or <3 standard deviations below the mean for the diagnosis of microcephaly. Fetal and infant magnetic resonance imaging images were processed to obtain a quantitative brain volumetric assessment. Diffusion weighted imaging sequences were processed to assess brain microstructure. Anthropometric, neurologic, auditory, and visual assessments were performed postnatally. Histopathologic assessment was included if patients opted for pregnancy termination.

RESULTS

All women (n=214) had been referred for Zika virus symptoms during pregnancy that affected themselves or their partners or if fetal anomalies that are compatible with congenital Zika virus syndrome were detected. A total of 12 pregnant patients with laboratory confirmation of Zika virus infection were diagnosed with fetal brain malformations. Most common findings that were assessed by prenatal and postnatal imaging were brain volume loss (92%), calcifications (92%), callosal anomalies (100%), cortical malformations (89%), and ventriculomegaly (92%). Results from fetal brain volumetric assessment by magnetic resonance imaging showed that 1 of the most common findings associated with microcephaly was reduced supratentorial brain parenchyma and increased subarachnoid cerebrospinal fluid. Diffusion weighted imaging analyses of apparent diffusion coefficient values showed microstructural changes. Microcephaly was present in 33.3-58.3% of the cases at referral and was present at delivery in 55.6-77.8% of cases. At birth, most of the affected neonates (55.6-77.8%) had head circumference measurements >3 standard deviations below the mean. Postnatal imaging studies confirmed brain malformations that were detected prenatally. Auditory screening results were normal in 2 cases that were assessed. Visual screening showed different anomalies in 2 of the 3 cases that were examined. Pathologic results that were obtained from 2 of the 3 cases who opted for termination showed similar signs of abnormalities in the central nervous system and placental analyses, including brain microcalcifications.

CONCLUSION

Congenital microcephaly is not an optimal screening method for congenital Zika virus syndrome, because it may not accompany other evident and preceding brain findings; microcephaly could be an endpoint of the disease that results from progressive changes that are related to brain volume loss. Long-term studies are needed to understand the clinical and developmental relevance of these findings.

Advances in Diagnosis, Surveillance, and Monitoring of Zika Virus: An Update

Zika virus (ZIKV) is associated with numerous human health-related disorders, including fetal microcephaly, neurological signs, and autoimmune disorders such as Guillain-Barré syndrome (GBS). Perceiving the ZIKA associated losses, in 2016, the World Health Organization (WHO) declared it as a global public health emergency. In consequence, an upsurge in the research on ZIKV was seen around the globe, with significant attainments over developing several effective diagnostics, drugs, therapies, and vaccines countering this life-threatening virus at an early step. State-of-art tools developed led the researchers to explore virus at the molecular level, and in-depth epidemiological investigations to understand the reason for increased pathogenicity and different clinical manifestations. These days, ZIKV infection is diagnosed based on clinical manifestations, along with serological and molecular detection tools. As, isolation of ZIKV is a tedious task; molecular assays such as reverse transcription-polymerase chain reaction (RT-PCR), real-time qRT-PCR, loop-mediated isothermal amplification (LAMP), lateral flow assays (LFAs), biosensors, nucleic acid sequence-based amplification (NASBA) tests, strand invasion-based amplification tests and immune assays like enzyme-linked immunosorbent assay (ELISA) are in-use to ascertain the ZIKV infection or Zika fever. Herein, this review highlights the recent advances in the diagnosis, surveillance, and monitoring of ZIKV. These new insights gained from the recent advances can aid in the rapid and definitive detection of this virus and/or Zika fever. The summarized information will aid the strategies to design and adopt effective prevention and control strategies to counter this viral pathogen of great public health concern.

Zika in the Americas, year 2: What have we learned? What gaps remain? A report from the Global Virus Network

In response to the outbreak of Zika virus (ZIKV) infection in the Western Hemisphere and the recognition of a causal association with fetal malformations, the Global Virus Network (GVN) assembled an international taskforce of virologists to promote basic research, recommend public health measures and encourage the rapid development of vaccines, antiviral therapies and new diagnostic tests. In this article, taskforce members and other experts review what has been learned about ZIKV-induced disease in humans, its modes of transmission and the cause and nature of associated congenital manifestations. After describing the make-up of the taskforce, we summarize the emergence of ZIKV in the Americas, Africa and Asia, its spread by mosquitoes, and current control measures. We then review the spectrum of primary ZIKV-induced disease in adults and children, sites of persistent infection and sexual transmission, then examine what has been learned about maternal-fetal transmission and the congenital Zika syndrome, including knowledge obtained from studies in laboratory animals. Subsequent sections focus on vaccine development, antiviral therapeutics and new diagnostic tests. After reviewing current understanding of the mechanisms of emergence of Zika virus, we consider the likely future of the pandemic.

Zika Risk and Pregnancy in Clinical Practice: Ongoing Experience as the Outbreak Evolves

OBJECTIVE

To describe a single U.S. perinatal center's ongoing experience with evaluating pregnant patients with potential exposure to Zika virus infection.

METHODS

This is an institutional review board-approved longitudinal observational study from January to August 2016 from a single perinatal referral center. Patients who had traveled to or had sexual contact with a person who traveled to a region with documented local Zika virus transmission were included in the study. The aim of the study was to identify the rate of confirmed infection among pregnant women referred to our center with established risk factors for Zika virus acquisition. We also sought to characterize travel patterns that constituted risk, to identify rates of symptoms suggesting infection, and to potentially describe findings suggestive of congenital Zika virus infection in prenatal ultrasound evaluations.

RESULTS

We evaluated 185 pregnant women with potential Zika virus exposure. Testing was offered in accordance with the version of the Centers for Disease Control and Prevention guidelines in place at the time of the consultation visit. Geographic exposure data showed Mexico (44%), the Caribbean (17%), North America (16%), South America (13%), and Central America (9%) to be the most common areas in which potential exposure occurred. One hundred twenty-three (67%) patients reported insect bites and 19 (10%) patients reported symptoms. Overall, five (3% of all) patients had prenatal ultrasound findings suggestive of possible fetal Zika virus infection; all their Zika virus test results returned negative. These findings included microcephaly, echogenic intracardiac foci, and ventricular calcifications. Of the 153 Zika virus screening tests ordered, eight (5%) immunoglobulin M results returned positive or equivocal with only one positive through confirmatory testing. Overall, 1 of 185 (0.5%) of all those consulted and 1 of 153 (0.7%) of those tested had a confirmed Zika virus infection with no confirmed fetal or neonatal infections.

CONCLUSION

We identified low rates of confirmed maternal Zika virus infection in our cohort, but the number of patients described here demonstrates the magnitude of concern existing among both patients and physicians regarding possible perinatal Zika virus infection. It also underscores the need for health care providers to be prepared to answer questions, explain laboratory and ultrasound results, and describe testing options for concerned patients and their families.

Reducing Unintended Pregnancies as a Strategy to Avert Zika-Related Microcephaly Births in the United States: A Simulation Study

Introduction There is increasing evidence that infection with the Zika virus (ZIKV) during pregnancy can lead to severe brain abnormalities in infants exposed in utero. The objective of our analysis was to estimate the contribution of enhanced contraception access to averting ZIKV-related microcephaly births in the United States, alone and in combination with another possible strategy, anti-ZIKV vaccination. Methods We used Monte Carlo sampling techniques (n = 100,000 simulations) to estimate the number of microcephaly births expected under strategies of enhanced contraception only, vaccination only, both enhanced contraception and vaccination, and status quo (no intervention). Enhanced contraceptive access was assumed to reduce unintended pregnancy rates by 46% and anti-ZIKV vaccination was assumed to be 90% effective. Plausible values for effectiveness of enhanced contraceptive access, ZIKV cumulative incidence, ZIKV-related microcephaly risk, and anti-ZIKV vaccination parameters were derived from the literature or best available knowledge. Results Enhanced contraceptive access alone reduced the median number of ZIKV-related microcephaly births by 16% (95% simulation interval: 5, 23), while the anti-ZIKV vaccine alone reduced these births by 9% (95% SI: 0, 18), 45% (95% SI: 36, 54), and 81% (95% SI: 71, 91), under conservative (10% vaccine uptake), moderate (50% vaccine uptake), and optimistic (90% vaccine uptake) scenarios, respectively. The reduction in ZIKV-related microcephaly births was always greater if both interventions were employed. Discussion Enhanced contraceptive access alone has the ability to produce a meaningful reduction in microcephaly births, and could provide an important adjuvant prevention strategy even following the development of a highly-effective anti-ZIKV vaccine.

First Neonatal Demise with Travel-Associated Zika Virus Infection in the United States of America

Zika virus is increasingly recognized as a fetal pathogen worldwide. We describe the first case of neonatal demise with travel-associated Zika virus infection in the United States of America, including a novel prenatal ultrasound finding. A young Latina presented to our health care system in Southeast Texas for prenatal care at 23 weeks of gestation. Fetal Dandy-Walker malformation, asymmetric cerebral ventriculomegaly, single umbilical artery, hypoechoic fetal knee, dorsal foot edema, and mild polyhydramnios were noted upon initial screening prenatal sonography at 26 weeks. A growth-restricted, microcephalic, and arthrogrypotic infant was delivered alive at 36 weeks but died within an hour despite resuscitation. The neonatal karyotype was normal. Flavivirus IgM antibodies were identified in the serum of the puerpera, once she disclosed that she had traveled from El Salvador to Texas in the early second trimester. Zika virus was identified in the umbilical cord and neonatal brain. Fetal arthritis may precede congenital arthrogryposis in cases of Zika virus infection and may be detectable by prenatal sonography. Physician and health care system vigilance is required to optimally address the significant and enduring Zika virus global health threat.

Testing for Zika virus infection in pregnancy: key concepts to deal with an emerging epidemic

Zika virus is an emerging mosquito-borne (Aedes genus) arbovirus of the Flaviviridae family. Following epidemics in Micronesia and French Polynesia during the past decade, more recent Zika virus infection outbreaks were first reported in South America as early as May 2013 and spread to now 50 countries throughout the Americas. Although no other flavivirus has previously been known to cause major fetal malformations following perinatal infection, reports of a causal link between Zika virus and microcephaly, brain and ocular malformations, and fetal loss emerged from hard-hit regions of Brazil by October 2015. Among the minority of infected women with symptoms, clinical manifestations of Zika virus infection may include fever, headache, arthralgia, myalgia, and maculopapular rash; however, only 1 of every 4-5 people who are infected have any symptoms. Thus, clinical symptom reporting is an ineffective screening tool for the relative risk assessment of Zika virus infection in the majority of patients. As previously occurred with other largely asymptomatic viral infections posing perinatal transmission risk (such as HIV or cytomegalovirus), we must develop and implement rapid, sensitive, and specific screening and diagnostic testing for both viral detection and estimation of timing of exposure. Unfortunately, despite an unprecedented surge in attempts to rapidly advance perinatal clinical testing for a previously obscure arbovirus, there are several ongoing hindrances to molecular- and sonographic-based screening and diagnosis of congenital Zika virus infection. These include the following: (1) difficulty in estimating the timing of exposure for women living in endemic areas and thus limited interpretability of immunoglobulin M serologies; (2) cross-reaction of immunoglobulin serologies with other endemic flaviruses, such as dengue; (3) persistent viremia and viruria in pregnancy weeks to months after primary exposure; and (4) fetal brain malformations and anomalies preceding the sonographic detection of microcephaly. In this commentary, we discuss screening and diagnostic considerations that are grounded not only in the realities of current obstetrical practice in a largely global population but also in basic immunology and virology. We review recent epidemiological data pertaining to the risk of congenital Zika virus malformations based on trimester of exposure and consider side by side with emerging data demonstrating replication of Zika virus in placental and fetal tissue throughout gestation. We discuss limitations to ultrasound based strategies that rely largely or solely on the detection of microcephaly and provide alternative neurosonographic approaches for the detection of malformations that may precede or occur independent of a small head circumference. This expert review provides information that is of value for the following: (1) obstetrician, maternal-fetal medicine specialist, midwife, patient, and family in cases of suspected Zika virus infection; (2) review of the methodology for laboratory testing to explore the presence of the virus and the immune response; (3) ultrasound-based assessment of the fetus suspected to be exposed to Zika virus with particular emphasis on the central nervous system; and (4) identification of areas ready for development.

Identifying birth defects in automated data sources in the Vaccine Safety Datalink

PURPOSE

The Vaccine Safety Datalink (VSD), a collaboration between the Centers for Disease Control and Prevention and several large healthcare organizations, aims to monitor safety of vaccines administered in the USA. We present definitions and prevalence estimates for major structural birth defects to be used in studies of maternal vaccine safety.

METHODS

In this observational study, we created and refined algorithms for identifying major structural birth defects from electronic healthcare data, conducted formal chart reviews for severe cardiac defects, and conducted limited chart validation for other defects. We estimated prevalence for selected defects by VSD site and birth year and compared these estimates to those in a US and European surveillance system.

RESULTS

We developed algorithms to enumerate >50 major structural birth defects from standardized administrative and healthcare data based on utilization patterns and expert opinion, applying criteria for number, timing, and setting of diagnoses. Our birth cohort included 497 894 infants across seven sites. The period prevalence for all selected major birth defects in the VSD from 2004 to 2013 was 1.7 per 100 live births. Cardiac defects were most common (65.4 per 10 000 live births), with one-fourth classified as severe, requiring emergent intervention. For most major structural birth defects, prevalence estimates were stable over time and across sites and similar to those reported in other population-based surveillance systems.

CONCLUSIONS

Our algorithms can efficiently identify many major structural birth defects in large healthcare datasets and can be used in studies evaluating the safety of vaccines administered to pregnant women. Copyright © 2017 John Wiley & Sons, Ltd.

Laboratory Diagnosis of Zika Virus Infection

CONTEXT

-The rapid and accurate diagnosis of Zika virus infection is an international priority.

OBJECTIVE

-To review current recommendations, methods, limitations, and priorities for Zika virus testing.

DATA SOURCES

-Sources include published literature, public health recommendations, laboratory procedures, and testing experience.

CONCLUSIONS

-Until recently, the laboratory diagnosis of Zika infection was confined to public health or research laboratories that prepared their own reagents, and test capacity has been limited. Furthermore, Zika cross-reacts serologically with other flaviviruses, such as dengue, West Nile, and yellow fever. Current or past infection, or even vaccination with another flavivirus, will often cause false-positive or uninterpretable Zika serology results. Detection of viral RNA during acute infection using nucleic acid amplification tests provides more specific results, and a number of commercial nucleic acid amplification tests have received emergency use authorization. In addition to serum, testing of whole blood and urine is recommended because of the higher vial loads and longer duration of shedding. However, nucleic acid amplification testing has limited utility because many patients are asymptomatic or present for testing after the brief period of Zika shedding has passed. Thus, the greatest need and most difficult challenge is development of accurate antibody tests for the diagnosis of recent Zika infection. Research is urgently needed to identify Zika virus epitopes that do not cross-react with other flavivirus antigens. New information is emerging at a rapid pace and, with ongoing public-private and international collaborations and government support, it is hoped that rapid progress will be made in developing robust and widely applicable diagnostic tools.

Available Evidence of Association between Zika Virus and Microcephaly

OBJECTIVE

To clarify the possible association between the Zika virus (ZIKV) and microcephaly and understand where we are in terms of research and the debate on the causation between mild maternal clinical features and severe fetal microcephaly.

DATA SOURCES

We did a comprehensive literature review with the keywords "zika" and/or "microcephaly" from inception to May 27, 2016, with PubMed.

STUDY SELECTION

Studies were included and analyzed if they met all of the following criteria: "probable or confirmed infant microcephaly" and "probable or confirmed ZIKV infection among mothers or infants".

RESULTS

We emphasize the diagnosis of ZIKV infection, including maternal clinical manifestations, maternal and fetal laboratory confirmation, and possible autopsy if need. Other confounders that may lead to microcephaly should be excluded from the study. We presented the results from clinical manifestations of ZIKV infection, testing methods evolving but the mechanism of microcephaly uncertain, flexible definition challenging the diagnosis of microcephaly, and limited causal reference on pregnant women. We made analog comparison of severe acute respiratory syndrome and chikungunya virus in terms of DNA mutation and global movement to provide further research recommendation. The chance of catch-up growth may decrease the number of pervious "diagnosed" microcephaly.

CONCLUSIONS

There are some evidence available through mice models and direct isolation of ZIKV in affected pregnancies on kindly causal relationship but not convincible enough. We analyzed and presented the weakness or limitation of published reports with the desire to shed light to further study directions.

The global threat of Zika virus to pregnancy: epidemiology, clinical perspectives, mechanisms, and impact

Zika virus (ZIKV) is a mosquito-borne flavivirus that has newly emerged as a significant global threat, especially to pregnancy. Recent major outbreaks in the Pacific and in Central and South America have been associated with an increased incidence of microcephaly and other abnormalities of the central nervous system in neonates. The causal link between ZIKV infection during pregnancy and microcephaly is now strongly supported. Over 2 billion people live in regions conducive to ZIKV transmission, with ~4 million infections in the Americas predicted for 2016. Given the scale of the current pandemic and the serious and long-term consequences of infection during pregnancy, the impact of ZIKV on health services and affected communities could be enormous. This further highlights the need for a rapid global public health and research response to ZIKV to limit and prevent its impact through the development of therapeutics, vaccines, and improved diagnostics. Here we review the epidemiology of ZIKV; the threat to pregnancy; the clinical consequences and broader impact of ZIKV infections; and the virus biology underpinning new interventions, diagnostics, and insights into the mechanisms of disease.

Zika Virus and Pregnancy: A Review of the Literature and Clinical Considerations

The latest Zika virus (ZIKV) outbreak has reached epidemic proportions as it spreads throughout South and Central America. In November 2015, the Brazilian Ministry of Health reported a 20-fold increase in the number of cases of neonatal microcephaly, which corresponds geographically and temporally to the ZIKV outbreak. Case reports have provided some evidence of a causal link between maternal ZIKV infection, fetal microcephaly, and intracranial calcifications. The sparse data regarding ZIKV in pregnancy come solely from case reports and personal communications, and recommendations for management of ZIKV exposure during pregnancy are rapidly evolving. Our objective is to review and synthesize the current literature regarding ZIKV as it pertains to pregnancy and provide some assistance to clinicians who may have to manage a pregnant patient with potential exposure to ZIKV. We will also explore certain aspects of related viruses in pregnancy in hopes to shed light on this little-known topic.

Zika virus: History, emergence, biology, and prospects for control

Zika virus (ZIKV), a previously obscure flavivirus closely related to dengue, West Nile, Japanese encephalitis and yellow fever viruses, has emerged explosively since 2007 to cause a series of epidemics in Micronesia, the South Pacific, and most recently the Americas. After its putative evolution in sub-Saharan Africa, ZIKV spread in the distant past to Asia and has probably emerged on multiple occasions into urban transmission cycles involving Aedes (Stegomyia) spp. mosquitoes and human amplification hosts, accompanied by a relatively mild dengue-like illness. The unprecedented numbers of people infected during recent outbreaks in the South Pacific and the Americas may have resulted in enough ZIKV infections to notice relatively rare congenital microcephaly and Guillain-Barré syndromes. Another hypothesis is that phenotypic changes in Asian lineage ZIKV strains led to these disease outcomes. Here, we review potential strategies to control the ongoing outbreak through vector-centric approaches as well as the prospects for the development of vaccines and therapeutics.