Ocular and uteroplacental pathology in a macaque pregnancy with congenital Zika virus infection

Decidual leukocytes respond to African lineage Zika virus infection with mild anti-inflammatory changes during acute infection in rhesus macaques

Zika virus (ZIKV) can be vertically transmitted during pregnancy resulting in a range of adverse pregnancy outcomes. The decidua is commonly found to be infected by ZIKV, yet the acute immune response to infection remains understudied in vivo. We hypothesized that in vivo African-lineage ZIKV infection induces a pro-inflammatory response in the decidua. To test this hypothesis, we evaluated the decidua in pregnant rhesus macaques within the first two weeks following infection with an African-lineage ZIKV and compared our findings to gestationally aged-matched controls. Decidual leukocytes were phenotypically evaluated using spectral flow cytometry, and cytokines and chemokines were measured in tissue homogenates from the decidua, placenta, and fetal membranes. The results of this study did not support our hypothesis. Although ZIKV RNA was detected in the decidual tissue samples from all ZIKV infected dams, phenotypic changes in decidual leukocytes and differences in cytokine profiles suggest that the decidua undergoes mild anti-inflammatory changes in response to that infection. Our findings emphasize the immunological state of the gravid uterus as a relatively immune privileged site that prioritizes tolerance of the fetus over mounting a pro-inflammatory response to clear infection.

Deciphering decidual leukocyte traffic with serial intravascular staining

The decidual immunome is dynamic, dramatically changing its composition across gestation. Early pregnancy is dominated by decidual NK cells, with a shift towards T cells later in pregnancy. However, the degree, timing, and subset-specific nature of leukocyte traffic between the decidua and systemic circulation during gestation remains poorly understood. Herein, we employed intravascular staining in pregnant C57BL/6J mice and cynomolgus macaques (Macaca fascicularis) to examine leukocyte traffic into the decidual basalis during pregnancy. Timed-mated or virgin mice were tail-vein injected with labelled αCD45 antibodies 24 hours and 5 minutes before sacrifice. Pregnant cynomolgus macaques (GD155) were infused with labelled αCD45 at 2 hours or 5 mins before necropsy. Decidual cells were isolated and resulting suspensions analyzed by flow cytometry. We found that the proportion of intravascular (IVAs)-negative leukocytes (cells labeled by the 24h infusion of αCD45 or unlabeled) decreased across murine gestation while recent immigrants (24h label only) increased in mid- to late-gestation. In the cynomolgus model our data confirmed differential labeling of decidual leukocytes by the infused antibody, with the 5 min infused animal having a higher proportion of IVAs+ cells compared to the 2hr infused animal. Decidual tissue sections from both macaques showed the presence of intravascularly labeled cells, either in proximity to blood vessels (5min infused animal) or deeper into decidual stroma (2hr infused animal). These results demonstrate the value of serial intravascular staining as a sensitive tool for defining decidual leukocyte traffic during pregnancy.

Maternal, placental and fetal response to a non-viral, polymeric nanoparticle gene therapy in nonhuman primates

Background

Currently, there are no placenta-targeted treatments to alter the in utero environment. Water-soluble polymers have a distinguished record of clinical relevance outside of pregnancy. We have demonstrated the effective delivery of polymer-based nanoparticles containing a non-viral human insulin-like 1 growth factor ( IGF1 ) transgene to correct placental insufficiency in small animal models of fetal growth restriction (FGR). Our goal was to extend these studies to the pregnant nonhuman primate (NHP) and assess maternal, placental and fetal responses to nanoparticle-mediated IGF1 treatment.

Methods

Pregnant macaques underwent ultrasound-guided intraplacental injections of nanoparticles ( GFP- or IGF1- expressing plasmid under the control of the trophoblast-specific PLAC1 promoter complexed with a HPMA-DMEAMA co-polymer) at approximately gestational day 100 (term = 165 days). Fetectomy was performed 24 h ( GFP ; n =1), 48 h ( IGF1 ; n = 3) or 10 days ( IGF1 ; n = 3) after nanoparticle delivery. Routine pathological assessment was performed on biopsied maternal tissues, and placental and fetal tissues. Maternal blood was analyzed for complete blood count (CBC), immunomodulatory proteins and growth factors, progesterone (P4) and estradiol (E2). Placental ERK/AKT/mTOR signaling was assessed using western blot and qPCR.

Findings

Fluorescent microscopy and in situ hybridization confirmed placental uptake and transgene expression in villous syncytiotrophoblast. No off-target expression was observed in maternal and fetal tissues. Histopathological assessment of the placenta recorded observations not necessarily related to the IGF1 nanoparticle treatment. In maternal blood, CBCs, P4 and E2 remained within the normal range for pregnant macaques across the treatment period. Changes to placental ERK and AKT signaling at 48 h and 10 d after IGF1 nanoparticle treatment indicated an upregulation in placental homeostatic mechanisms to prevent over activity in the normal pregnancy environment.

Interpretation

Maternal toxicity profile analysis and lack of adverse reaction to nanoparticle-mediated IGF1 treatment, combined with changes in placental signaling to maintain homeostasis indicates no deleterious impact of treatment.

Funding

National Institutes of Health, and Wisconsin National Primate Research Center.

Prenatal Zika virus exposure is associated with lateral geniculate nucleus abnormalities in juvenile rhesus macaques

Zika virus' neural tropism causes significant neural pathology, particularly in developing fetuses. One of the consistent findings from humans and animal models is that prenatal exposure to Zika virus (ZIKV) causes pathology in the eyes and visual pathways of the brain, although the extent to which this pathology persists over development is not clear. In the present report, we build upon our previous work which demonstrated that full-term rhesus monkey ( Macaca mulatta ) fetuses who were exposed to ZIKV early in gestation had significant pathological abnormalities to the organization of the lateral geniculate nucleus (LGN), a major hub of the visual network. The objective of the present work was to replicate those LGN findings and determine whether such pathology persisted across childhood development. We carried out histological analyses of the LGNs of two juvenile rhesus monkeys who were prenatally exposed to ZIKV and two age-matched controls. Pregnant rhesus monkeys were infected with ZIKV via the intravenous and intra-amniotic routes and tracked across development. Following sacrifice and perfusion, brains were subjected to quantitative neuroanatomical analyses with a focus on the size and structure of the LGN and its composite layers. Early fetal ZIKV exposure resulted in developmental abnormalities within the brains' visual pathway: specifically disorganization, blending of layers, laminar discontinuities, and regions of low cell density within the LGN. These abnormalities were not observed in the control animals. Our findings demonstrate that the ZIKV's damage to the LGN that occurs during fetal development persists into childhood.

Exacerbated Zika virus-induced neuropathology and microcephaly in fetuses of dengue-immune nonhuman primates

Zika virus (ZIKV) is a mosquito-borne flavivirus that can vertically transmit from mother to fetus, potentially causing congenital defects, including microcephaly. It is not fully understood why some fetuses experience severe complications after in utero exposure to ZIKV, whereas others do not. Given the antigenic similarity between ZIKV and the closely related virus dengue (DENV) and the potential of DENV-specific antibodies to enhance ZIKV disease severity in mice, we questioned whether maternal DENV immunity could influence fetal outcomes in a nonhuman primate model of ZIKV vertical transmission. We found significantly increased severity of congenital Zika syndrome (CZS) in fetuses of DENV-immune cynomolgus macaques infected with ZIKV in early pregnancy compared with naïve controls, which occurred despite no effect on maternal ZIKV infection or antibody responses. Ultrasound measurements of head circumference and biparietal diameter measurements taken sequentially throughout pregnancy demonstrated CZS in fetuses of DENV-immune pregnant macaques. Furthermore, severe CZS enhanced by DENV immunity was typified by reduced cortical thickness and increased frequency of neuronal death, hemorrhaging, cellular infiltrations, calcifications, and lissencephaly in fetal brains. This study shows that maternal immunity to DENV can worsen ZIKV neurological outcomes in fetal primates, and it provides an animal model of vertical transmission closely approximating human developmental timelines that could be used to investigate severe ZIKV disease outcomes and interventions in fetuses.

Vertical transmission of African-lineage Zika virus through the fetal membranes in a rhesus macaque (Macaca mulatta) model

Zika virus (ZIKV) can be transmitted vertically from mother to fetus during pregnancy, resulting in a range of outcomes including severe birth defects and fetal/infant death. Potential pathways of vertical transmission in utero have been proposed but remain undefined. Identifying the timing and routes of vertical transmission of ZIKV may help us identify when interventions would be most effective. Furthermore, understanding what barriers ZIKV overcomes to effect vertical transmission may help improve models for evaluating infection by other pathogens during pregnancy. To determine the pathways of vertical transmission, we inoculated 12 pregnant rhesus macaques with an African-lineage ZIKV at gestational day 30 (term is 165 days). Eight pregnancies were surgically terminated at either seven or 14 days post-maternal infection. Maternal-fetal interface and fetal tissues and fluids were collected and evaluated for ZIKV using RT-qPCR, in situ hybridization, immunohistochemistry, and plaque assays. Four additional pregnant macaques were inoculated and terminally perfused with 4% paraformaldehyde at three, six, nine, or ten days post-maternal inoculation. For these four cases, the entire fixed pregnant uterus was evaluated with in situ hybridization for ZIKV RNA. We determined that ZIKV can reach the MFI by six days after infection and infect the fetus by ten days. Infection of the chorionic membrane and the extraembryonic coelomic fluid preceded infection of the fetus and the mesenchymal tissue of the placental villi. We did not find evidence to support a transplacental route of ZIKV vertical transmission via infection of syncytiotrophoblasts or villous cytotrophoblasts. The pattern of infection observed in the maternal-fetal interface provides evidence of paraplacental vertical ZIKV transmission through the chorionic membrane, the outer layer of the fetal membranes.

Infection of the maternal-fetal interface and vertical transmission following low-dose inoculation of pregnant rhesus macaques (Macaca mulatta) with an African-lineage Zika virus

BACKGROUND

Congenital Zika virus (ZIKV) infection can result in birth defects, including malformations in the fetal brain and visual system. There are two distinct genetic lineages of ZIKV: African and Asian. Asian-lineage ZIKVs have been associated with adverse pregnancy outcomes in humans; however, recent evidence from experimental models suggests that African-lineage viruses can also be vertically transmitted and cause fetal harm.

METHODOLOGY/PRINCIPAL FINDINGS

To evaluate the pathway of vertical transmission of African-lineage ZIKV, we inoculated nine pregnant rhesus macaques (Macaca mulatta) subcutaneously with 44 plaque-forming units of a ZIKV strain from Senegal, (ZIKV-DAK). Dams were inoculated either at gestational day 30 or 45. Following maternal inoculation, pregnancies were surgically terminated seven or 14 days later and fetal and maternal-fetal interface tissues were collected and evaluated. Infection in the dams was evaluated via plasma viremia and neutralizing antibody titers pre- and post- ZIKV inoculation. All dams became productively infected and developed strong neutralizing antibody responses. ZIKV RNA was detected in maternal-fetal interface tissues (placenta, decidua, and fetal membranes) by RT-qPCR and in situ hybridization. In situ hybridization detected ZIKV predominantly in the decidua and revealed that the fetal membranes may play a role in ZIKV vertical transmission. Infectious ZIKV was detected in the amniotic fluid of three pregnancies and one fetus had ZIKV RNA detected in multiple tissues. No significant pathology was observed in any fetus; and ZIKV did not have a substantial effect on the placenta.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates that a very low dose of African-lineage ZIKV can be vertically transmitted to the macaque fetus during pregnancy. The low inoculating dose used in this study suggests a low minimal infectious dose for rhesus macaques. Vertical transmission with a low dose in macaques further supports the high epidemic potential of African ZIKV strains.

Zika virus infection of retinal cells and the developing mouse eye induces host responses that contrasts to the brain and dengue virus infection

Zika virus (ZIKV) infection causes ocular and neurological pathologies with ZIKV-induction of developmental abnormalities following in utero infection a major concern. The study here has compared ZIKV and the related dengue virus (DENV) infection in the eye and brain. In vitro, both ZIKV and DENV could infect cell lines representing the retinal pigmented epithelium, endothelial cells, and Mueller cells, with distinct innate responses in each cell type. In a 1-day old mouse challenge model, both ZIKV and DENV infected the brain and eye by day 6 post-infection (pi). ZIKV was present at comparable levels in both tissues, with RNA increasing with time post-infection. DENV infected the brain, but RNA was detected in the eye of less than half of the mice challenged. NanoString analysis demonstrated comparable host responses in the brain for both viruses, including induction of mRNA for myosin light chain-2 (Mly2), and numerous antiviral and inflammatory genes. Notably, mRNA for multiple complement proteins were induced, but C2 and C4a were uniquely induced by ZIKV but not DENV. Consistent with the viral infection in the eye, DENV induced few responses while ZIKV induced substantial inflammatory and antiviral responses. Compared to the brain, ZIKV in the eye did not induce mRNAs such as C3, downregulated Retnla, and upregulated CSF-1. Morphologically, the ZIKV-infected retina demonstrated reduced formation of specific retinal layers. Thus, although ZIKV and DENV can both infect the eye and brain, there are distinct differences in host cell and tissue inflammatory responses that may be relevant to ZIKV replication and disease.

Frequent first-trimester pregnancy loss in rhesus macaques infected with African-lineage Zika virus

In the 2016 Zika virus (ZIKV) pandemic, a previously unrecognized risk of birth defects surfaced in babies whose mothers were infected with Asian-lineage ZIKV during pregnancy. Less is known about the impacts of gestational African-lineage ZIKV infections. Given high human immunodeficiency virus (HIV) burdens in regions where African-lineage ZIKV circulates, we evaluated whether pregnant rhesus macaques infected with simian immunodeficiency virus (SIV) have a higher risk of African-lineage ZIKV-associated birth defects. Remarkably, in both SIV+ and SIV- animals, ZIKV infection early in the first trimester caused a high incidence (78%) of spontaneous pregnancy loss within 20 days. These findings suggest a significant risk for early pregnancy loss associated with African-lineage ZIKV infection and provide the first consistent ZIKV-associated phenotype in macaques for testing medical countermeasures.

Differential Susceptibility of Fetal Retinal Pigment Epithelial Cells, hiPSC- Retinal Stem Cells, and Retinal Organoids to Zika Virus Infection

Zika virus (ZIKV) causes microcephaly and congenital eye disease. The cellular and molecular basis of congenital ZIKV infection are not well understood. Here, we utilized a biologically relevant cell-based system of human fetal retinal pigment epithelial cells (FRPEs), hiPSC-derived retinal stem cells (iRSCs), and retinal organoids to investigate ZIKV-mediated ocular cell injury processes. Our data show that FRPEs were highly susceptible to ZIKV infection exhibiting increased apoptosis, whereas iRSCs showed reduced susceptibility. Detailed transcriptomics and proteomics analyses of infected FRPEs were performed. Nucleoside analogue drug treatment inhibited ZIKV replication. Retinal organoids were susceptible to ZIKV infection. The Asian genotype ZIKV exhibited higher infectivity, induced profound inflammatory response, and dysregulated transcription factors involved in retinal organoid differentiation. Collectively, our study shows that ZIKV affects ocular cells at different developmental stages resulting in cellular injury and death, further providing molecular insight into the pathogenesis of congenital eye disease.

Early and mid-gestation Zika virus (ZIKV) infection in the olive baboon (Papio anubis) leads to fetal CNS pathology by term gestation

Zika virus (ZIKV) infection in pregnancy can produce catastrophic teratogenic damage to the developing fetus including microcephaly and congenital Zika syndrome (CZS). We previously described fetal CNS pathology occurring by three weeks post-ZIKV inoculation in Olive baboons at mid-gestation, including neuroinflammation, loss of radial glia (RG), RG fibers, neuroprogenitor cells (NPCs) resulting in disrupted NPC migration. In the present study, we explored fetal brain pathologies at term gestation resulting from ZIKV exposure during either first or second trimester in the Olive baboon. In all dams, vRNA in whole blood resolved after 7 days post inoculation (dpi). One first trimester infected dam aborted at 5 dpi. All dams developed IgM and IgG response to ZIKV with ZIKV IgG detected in fetal serum. Placental pathology and inflammation were observed including disruption of syncytiotrophoblast layers, delayed villous maturation, partially or fully thrombosed vessels, calcium mineralization and fibrin deposits. In the uterus, ZIKV was detected in ¾ first trimester but not in second trimester infected dams. While ZIKV was not detected in any fetal tissue at term, all fetuses exhibited varying degrees of neuropathology. Fetal brains from ZIKV inoculated dams exhibited a range of gross brain pathologies including irregularities of the major gyri and sulci of the cerebral cortex and cerebellar pathology. Frontal cortices of ZIKV fetuses showed a general disorganization of the six-layered cortex with degree of disorganization varying among the fetuses from the two groups. Frontal cortices from ZIKV inoculation in the first but not second trimester exhibited increased microglia, and in both trimester ZIKV inoculation, increased astrocyte numbers (white matter). In the cerebellum, increased microglia were observed in fetuses from both first and second trimester inoculation. In first trimester ZIKV inoculation, decreased oligodendrocyte precursor cell populations were observed in fetal cerebellar white matter. In general, our observations are in accordance with those described in human ZIKV infected fetuses.

Human immune globulin treatment controls Zika viremia in pregnant rhesus macaques

There are currently no approved drugs to treat Zika virus (ZIKV) infection during pregnancy. Hyperimmune globulin products such as VARIZIG and WinRho are FDA-approved to treat conditions during pregnancy such as Varicella Zoster virus infection and Rh-incompatibility. We administered ZIKV-specific human immune globulin as a treatment in pregnant rhesus macaques one day after subcutaneous ZIKV infection. All animals controlled ZIKV viremia following the treatment and generated robust levels of anti-Zika virus antibodies in their blood. No adverse fetal or infant outcomes were identified in the treated animals, yet the placebo control treated animals also did not have signs related to congenital Zika syndrome (CZS). Human immune globulin may be a viable prophylaxis and treatment option for ZIKV infection during pregnancy, however, more studies are required to fully assess the impact of this treatment to prevent CZS.

Chronic Inflammatory Placental Disorders Associated With Recurrent Adverse Pregnancy Outcome

Chronic inflammatory placental disorders are a group of rare but devastating gestational syndromes associated with adverse pregnancy outcome. This review focuses on three related conditions: villitis of unknown etiology (VUE), chronic histiocytic intervillositis (CHI) and massive perivillous fibrin deposition (MPFD). The hallmark of these disorders is infiltration of the placental architecture by maternal immune cells and disruption of the intervillous space, where gas exchange between the mother and fetus occurs. Currently, they can only be detected through histopathological examination of the placenta after a pregnancy has ended. All three are associated with a significant risk of recurrence in subsequent pregnancies. Villitis of unknown etiology is characterised by a destructive infiltrate of maternal CD8+ T lymphocytes invading into the chorionic villi, combined with activation of fetal villous macrophages. The diagnosis can only be made when an infectious aetiology has been excluded. VUE becomes more common as pregnancy progresses and is frequently seen with normal pregnancy outcome. However, severe early-onset villitis is usually associated with fetal growth restriction and recurrent pregnancy loss. Chronic histiocytic intervillositis is characterised by excessive accumulation of maternal CD68+ histiocytes in the intervillous space. It is associated with a wide spectrum of adverse pregnancy outcomes including high rates of first-trimester miscarriage, severe fetal growth restriction and late intrauterine fetal death. Intervillous histiocytes can also accumulate due to infection, including SARS-CoV-2, although this infection-induced intervillositis does not appear to recur. As with VUE, the diagnosis of CHI requires exclusion of an infectious cause. Women with recurrent CHI and their families are predisposed to autoimmune diseases, suggesting CHI may have an alloimmune pathology. This observation has driven attempts to prevent CHI with a wide range of maternal immunosuppression. Massive perivillous fibrin deposition is diagnosed when >25% of the intervillous space is occupied by fibrin, and is associated with fetal growth restriction and late intrauterine fetal death. Although not an inflammatory disorder per se, MPFD is frequently seen in association with both VUE and CHI. This review summarises current understanding of the prevalence, diagnostic features, clinical consequences, immune pathology and potential prophylaxis against recurrence in these three chronic inflammatory placental syndromes.

Neuroanatomical abnormalities in a nonhuman primate model of congenital Zika virus infection

We evaluated neuropathological consequences of fetal ZIKV exposure in rhesus monkeys, a translatable animal model for human neural development, by carrying out quantitative neuroanatomical analyses of the nearly full-term brains of fetuses infected with ZIKV and procedure-matched controls. For each animal, a complete cerebral hemisphere was evaluated using immunohistochemical (IHC) and neuroanatomical techniques to detect virus, identify affected cell types, and evaluate gross neuroanatomical abnormalities. IHC staining revealed the presence of ZIKV in the frontal lobe, which contained activated microglia and showed increased apoptosis of immature neurons. ZIKV-infected animals exhibited macrostructural changes within the visual pathway. Regional differences tracked with the developmental timing of the brain, suggesting inflammatory processes related to viral infiltration swept through the cortex, followed by a wave of cell death resulting in morphological changes. These findings may help explain why some infants born with normal sized heads during the ZIKV epidemic manifest developmental challenges as they age.

Nonhuman Primate Models of Zika Virus Infection and Disease during Pregnancy

Since the explosive outbreak of Zika virus in Brazil and South/Central America in 2015–2016, the frequency of infections has subsided, but Zika virus remains present in this region as well as other tropical and sub-tropical areas of the globe. The most alarming aspect of Zika virus infection is its association with severe birth defects when infection occurs in pregnant women. Understanding the mechanism of Zika virus pathogenesis, which comprises features unique to Zika virus as well as shared with other teratogenic pathogens, is key to future prophylactic or therapeutic interventions. Nonhuman primate-based research has played a significant role in advancing our knowledge of Zika virus pathogenesis, especially with regard to fetal infection. This review summarizes what we have learned from these models and potential future research directions.

Differences in Placental Histology Between Zika Virus-infected Teenagers and Older Women

In pregnant women, Zika virus (ZIKV) is associated with a congenital syndrome, most frequently involving damage to embryo brain formation and the development of microcephaly. The mechanism(s) by which ZIKV enters the maternal-fetal interface and is transmitted to the fetus remains incompletely determined. We sought to evaluate histologic changes in the placenta of ZIKV-infected pregnant women and to determine if this varied by maternal age. Placental samples were obtained from 66 women, 33 of whom were positive for ZIKV. Histologic evaluations were performed on 4 areas of the placenta: fetal surface, maternal surface, umbilical cord, and membranes. Samples were analyzed by the tissue microarray technique and tested for CD4, CD8, CD20, CD68, FOXP3, and cyclooxygenase-2 expression. Data were evaluated using Fisher exact test. ZIKV infection was more frequent in women less than 18 yr of age (9/11, 81.8%) than in women above 18 yr old (24/55, 43.6%) (P=0.0440). ZIKV detection was associated with neutrophilic chorioamnionitis (P=0.0332) and with septal (P=0.0244) and villous (P=0.0534) calcification. Hofbauer cell hyperplasia (P=0.0260) and cyclooxygenase-2 expression (P=0.0346) were more prevalent in ZIKV-positive women aged 18 yr and below than in the older ZIKV-positive women. ZIKV infection during pregnancy occurs more frequently in adolescents and induces higher rates of damage at the maternal-fetal interface than in older women.

African-Lineage Zika Virus Replication Dynamics and Maternal-Fetal Interface Infection in Pregnant Rhesus Macaques

Following the Zika virus (ZIKV) outbreak in the Americas, ZIKV was causally associated with microcephaly and a range of neurological and developmental symptoms, termed congenital Zika syndrome (CZS). The viruses responsible for this outbreak belonged to the Asian lineage of ZIKV. However, in vitro and in vivo studies assessing the pathogenesis of African-lineage ZIKV demonstrated that African-lineage isolates often replicated to high titers and caused more-severe pathology than Asian-lineage isolates. To date, the pathogenesis of African-lineage ZIKV in a translational model, particularly during pregnancy, has not been rigorously characterized. Here, we infected four pregnant rhesus macaques with a low-passage-number strain of African-lineage ZIKV and compared its pathogenesis to those for a cohort of four pregnant rhesus macaques infected with an Asian-lineage isolate and a cohort of mock-inoculated controls. The viral replication kinetics for the two experimental groups were not significantly different, and both groups developed robust neutralizing antibody titers above levels considered to be protective. There was no evidence of significant fetal head growth restriction or gross fetal harm at delivery (1 to 1.5 weeks prior to full term) in either group. However, a significantly higher burden of ZIKV viral RNA (vRNA) was found in the maternal-fetal interface tissues of the macaques exposed to an African-lineage isolate. Our findings suggest that ZIKV of any genetic lineage poses a threat to pregnant individuals and their infants.

IMPORTANCE ZIKV was first identified in 1947 in Africa, but most of our knowledge of ZIKV is based on studies of the distinct Asian genetic lineage, which caused the outbreak in the Americas in 2015 to 2016. In its most recent update, the WHO stated that improved understanding of African-lineage ZIKV pathogenesis during pregnancy must be a priority. The recent detection of African-lineage isolates in Brazil underscores the need to understand the impact of these viruses. Here, we provide the first comprehensive assessment of African-lineage ZIKV infection during pregnancy in a translational nonhuman primate model. We show that African-lineage isolates replicate with kinetics similar to those of Asian-lineage isolates and can infect the placenta. However, there was no evidence of more-severe outcomes with African-lineage isolates. Our results highlight both the threat that African-lineage ZIKV poses to pregnant individuals and their infants and the need for epidemiological and translational in vivo studies with African-lineage ZIKV.

Non-human Primate Models to Investigate Mechanisms of Infection-Associated Fetal and Pediatric Injury, Teratogenesis and Stillbirth

A wide array of pathogens has the potential to injure the fetus and induce teratogenesis, the process by which mutations in fetal somatic cells lead to congenital malformations. Rubella virus was the first infectious disease to be linked to congenital malformations due to an infection in pregnancy, which can include congenital cataracts, microcephaly, hearing impairment and congenital heart disease. Currently, human cytomegalovirus (HCMV) is the leading infectious cause of congenital malformations globally, affecting 1 in every 200 infants. However, our knowledge of teratogenic viruses and pathogens is far from complete. New emerging infectious diseases may induce teratogenesis, similar to Zika virus (ZIKV) that caused a global pandemic in 2016-2017; thousands of neonates were born with congenital microcephaly due to ZIKV exposure in utero, which also included a spectrum of injuries to the brain, eyes and spinal cord. In addition to congenital anomalies, permanent injury to fetal and neonatal organs, preterm birth, stillbirth and spontaneous abortion are known consequences of a broader group of infectious diseases including group B streptococcus (GBS), Listeria monocytogenes, Influenza A virus (IAV), and Human Immunodeficiency Virus (HIV). Animal models are crucial for determining the mechanism of how these various infectious diseases induce teratogenesis or organ injury, as well as testing novel therapeutics for fetal or neonatal protection. Other mammalian models differ in many respects from human pregnancy including placentation, labor physiology, reproductive tract anatomy, timeline of fetal development and reproductive toxicology. In contrast, non-human primates (NHP) most closely resemble human pregnancy and exhibit key similarities that make them ideal for research to discover the mechanisms of injury and for testing vaccines and therapeutics to prevent teratogenesis, fetal and neonatal injury and adverse pregnancy outcomes (e.g., stillbirth or spontaneous abortion). In this review, we emphasize key contributions of the NHP model pre-clinical research for ZIKV, HCMV, HIV, IAV, L. monocytogenes, Ureaplasma species, and GBS. This work represents the foundation for development and testing of preventative and therapeutic strategies to inhibit infectious injury of human fetuses and neonates.

Early Embryonic Loss Following Intravaginal Zika Virus Challenge in Rhesus Macaques

Zika virus (ZIKV) is an arthropod-borne virus (arbovirus) and is primarily transmitted by Aedes species mosquitoes; however, ZIKV can also be sexually transmitted. During the initial epidemic and in places where ZIKV is now considered endemic, it is difficult to disentangle the risks and contributions of sexual versus vector-borne transmission to adverse pregnancy outcomes. To examine the potential impact of sexual transmission of ZIKV on pregnancy outcome, we challenged three rhesus macaques (Macaca mulatta) three times intravaginally with 1 x 107 PFU of a low passage, African lineage ZIKV isolate (ZIKV-DAK) in the first trimester (~30 days gestational age). Samples were collected from all animals initially on days 3 through 10 post challenge, followed by twice, and then once weekly sample collection; ultrasound examinations were performed every 3-4 days then weekly as pregnancies progressed. All three dams had ZIKV RNA detectable in plasma on day 3 post-ZIKV challenge. At approximately 45 days gestation (17-18 days post-challenge), two of the three dams were found with nonviable embryos by ultrasound. Viral RNA was detected in recovered tissues and at the maternal-fetal interface (MFI) in both cases. The remaining viable pregnancy proceeded to near term (~155 days gestational age) and ZIKV RNA was detected at the MFI but not in fetal tissues. These results suggest that sexual transmission of ZIKV may represent an underappreciated risk of pregnancy loss during early gestation.

The promise of placental extracellular vesicles: models and challenges for diagnosing placental dysfunction in utero†

Monitoring the health of a pregnancy is of utmost importance to both the fetus and the mother. The diagnosis of pregnancy complications typically occurs after the manifestation of symptoms, and limited preventative measures or effective treatments are available. Traditionally, pregnancy health is evaluated by analyzing maternal serum hormone levels, genetic testing, ultrasonographic imaging, and monitoring maternal symptoms. However, researchers have reported a difference in extracellular vesicle (EV) quantity and cargo between healthy and at-risk pregnancies. Thus, placental EVs (PEVs) may help to understand normal and aberrant placental development, monitor pregnancy health in terms of developing placental pathologies, and assess the impact of environmental influences, such as infection, on pregnancy. The diagnostic potential of PEVs could allow for earlier detection of pregnancy complications via noninvasive sampling and frequent monitoring. Understanding how PEVs serve as a means of communication with maternal cells and recognizing their potential utility as a readout of placental health have sparked a growing interest in basic and translational research. However, to date, PEV research with animal models lags behind human studies. The strength of animal pregnancy models is that they can be used to assess placental pathologies in conjunction with isolation of PEVs from fluid samples at different time points throughout gestation. Assessing PEV cargo in animals within normal and complicated pregnancies will accelerate the translation of PEV analysis into the clinic for potential use in prognostics. We propose that appropriate animal models of human pregnancy complications must be established in the PEV field.

Evolution of ocular defects in infant macaques following in utero Zika virus infection

Congenital Zika syndrome (CZS) is associated with microcephaly and various neurological, musculoskeletal, and ocular abnormalities, but the long-term pathogenesis and postnatal progression of ocular defects in infants are not well characterized. Rhesus macaques are superior to rodents as models of CZS because they are natural hosts of the virus and share similar immune and ocular characteristics, including blood–retinal barrier characteristics and the unique presence of a macula. Using a previously described model of CZS, we infected pregnant rhesus macaques with Zika virus (ZIKV) during the late first trimester and characterized postnatal ocular development and evolution of ocular defects in 2 infant macaques over 2 years. We found that one of them exhibited colobomatous chorioretinal atrophic lesions with macular and vascular dragging as well as retinal thinning caused by loss of retinal ganglion neuron and photoreceptor layers. Despite these congenital ocular malformations, axial elongation and retinal development in these infants progressed at normal rates compared with healthy animals. The ZIKV-exposed infants displayed a rapid loss of ZIKV-specific antibodies, suggesting the absence of viral replication after birth, and did not show any behavioral or neurological defects postnatally. Our findings suggest that ZIKV infection during early pregnancy can impact fetal retinal development and cause congenital ocular anomalies but does not appear to affect postnatal ocular growth.

Two Sides of a Coin: a Zika Virus Mutation Selected in Pregnant Rhesus Macaques Promotes Fetal Infection in Mice but at a Cost of Reduced Fitness in Nonpregnant Macaques and Diminished Transmissibility by Vectors

Although Zika virus infection of pregnant women can result in congenital Zika syndrome, the factors that cause the syndrome in some but not all infected mothers are still unclear. We identified a mutation that was present in some ZIKV genomes in experimentally inoculated pregnant rhesus macaques and their fetuses. Although we did not find an association between the presence of the mutation and fetal death, we performed additional studies with ZIKV with the mutation in nonpregnant macaques, pregnant mice, and mosquitoes. We observed that the mutation increased the ability of the virus to infect mouse fetuses but decreased its capacity to produce high levels of virus in the blood of nonpregnant macaques and to be transmitted by mosquitoes. This study shows that mutations in mosquito-borne viruses like ZIKV that increase fitness in pregnant vertebrates may not spread in outbreaks when they compromise transmission via mosquitoes and fitness in nonpregnant hosts.

Although fetal death is now understood to be a severe outcome of congenital Zika syndrome, the role of viral genetics is still unclear. We sequenced Zika virus (ZIKV) from a rhesus macaque fetus that died after inoculation and identified a single intrahost substitution, M1404I, in the ZIKV polyprotein, located in nonstructural protein 2B (NS2B). Targeted sequencing flanking position 1404 in 9 additional macaque mothers and their fetuses identified M1404I at a subconsensus frequency in the majority (5 of 9, 56%) of animals and some of their fetuses. Despite its repeated presence in pregnant macaques, M1404I has occurred rarely in humans since 2015. Since the primary ZIKV transmission cycle is human-mosquito-human, mutations in one host must be retained in the alternate host to be perpetuated. We hypothesized that ZIKV I1404 increases viral fitness in nonpregnant macaques and pregnant mice but is less efficiently transmitted by vectors, explaining its low frequency in humans during outbreaks. By examining competitive fitness relative to that of ZIKV M1404, we observed that ZIKV I1404 produced lower viremias in nonpregnant macaques and was a weaker competitor in tissues. In pregnant wild-type mice, ZIKV I1404 increased the magnitude and rate of placental infection and conferred fetal infection, in contrast to ZIKV M1404, which was not detected in fetuses. Although infection and dissemination rates were not different, Aedes aegypti mosquitoes transmitted ZIKV I1404 more poorly than ZIKV M1404. Our data highlight the complexity of arbovirus mutation-fitness dynamics and suggest that intrahost ZIKV mutations capable of augmenting fitness in pregnant vertebrates may not necessarily spread efficiently via mosquitoes during epidemics.

IMPORTANCE Although Zika virus infection of pregnant women can result in congenital Zika syndrome, the factors that cause the syndrome in some but not all infected mothers are still unclear. We identified a mutation that was present in some ZIKV genomes in experimentally inoculated pregnant rhesus macaques and their fetuses. Although we did not find an association between the presence of the mutation and fetal death, we performed additional studies with ZIKV with the mutation in nonpregnant macaques, pregnant mice, and mosquitoes. We observed that the mutation increased the ability of the virus to infect mouse fetuses but decreased its capacity to produce high levels of virus in the blood of nonpregnant macaques and to be transmitted by mosquitoes. This study shows that mutations in mosquito-borne viruses like ZIKV that increase fitness in pregnant vertebrates may not spread in outbreaks when they compromise transmission via mosquitoes and fitness in nonpregnant hosts.

Serum Proteomics Reveals Alterations in Protease Activity, Axon Guidance, and Visual Phototransduction Pathways in Infants With In Utero Exposure to Zika Virus Without Congenital Zika Syndrome

In 2015, ZIKV infection attracted international attention during an epidemic in the Americas, when neurological disorders were reported in infants who had their mothers exposed to ZIKV during pregnancy. World Health Organization (WHO) epidemiological data show that 5 to 15% of neonates exposed to ZIKV in the uterus have complications included in abnormalities related to Congenital Zika Syndrome (CZS). The risk of complications after birth is not well documented, however, clinical evidence shows that 6% of infants exposed to ZIKV during pregnancy have complications present at birth, and this rate rises to 14% when medical monitoring is performed in all exposed infants, regardless of birth condition. Thus, the evaluation and monitoring of all exposed infants are of foremost importance as the development of late complications has been increasingly supported by clinical evidence. The identification of changes in protein profile of infants exposed to ZIKV without CZS could provide valuable findings to better understand molecular changes in this cohort. Here, we use a shotgun-proteomics approach to investigate alterations in the serum of infants without CZS symptoms but exposed to intrauterine ZIKV (ZIKV) compared to unexposed controls (CTRL). A complex pattern of differentially expressed proteins was identified, highlighting the dysregulation of proteins involved in axon orientation, visual phototransduction, and global protease activity in children exposed to ZIKV without CZS. These data support the importance of monitoring children exposed to ZIKV during gestation and without early CZS symptoms. Our study is the first to assess molecular evidence of possible late disorders in children victims of the ZIKV outbreak in the Americas. We emphasize the importance of medical monitoring of symptomatic and asymptomatic children, as apparently unexplained late neurological and eye disorders may be due to intrauterine ZIKV exposure.

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

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

Quantitative definition of neurobehavior, vision, hearing and brain volumes in macaques congenitally exposed to Zika virus

Congenital Zika virus (ZIKV) exposure results in a spectrum of disease ranging from severe birth defects to delayed onset neurodevelopmental deficits. ZIKV-related neuropathogenesis, predictors of birth defects, and neurodevelopmental deficits are not well defined in people. Here we assess the methodological and statistical feasibility of a congenital ZIKV exposure macaque model for identifying infant neurobehavior and brain abnormalities that may underlie neurodevelopmental deficits. We inoculated five pregnant macaques with ZIKV and mock-inoculated one macaque in the first trimester. Following birth, growth, ocular structure/function, brain structure, hearing, histopathology, and neurobehavior were quantitatively assessed during the first week of life. We identified the typical pregnancy outcomes of congenital ZIKV infection, with fetal demise and placental abnormalities. We estimated sample sizes needed to define differences between groups and demonstrated that future studies quantifying brain region volumes, retinal structure, hearing, and visual pathway function require a sample size of 14 animals per group (14 ZIKV, 14 control) to detect statistically significant differences in at least half of the infant exam parameters. Establishing the parameters for future studies of neurodevelopmental outcomes following congenital ZIKV exposure in macaques is essential for robust and rigorous experimental design.

Zika virus in rhesus macaque semen and reproductive tract tissues: a pilot study of acute infection†

Although sexual transmission of Zika virus (ZIKV) is well-documented, the viral reservoir(s) in the male reproductive tract remains uncertain in humans and immune-intact animal models. We evaluated the presence of ZIKV in a rhesus macaque pilot study to determine persistence in semen, assess the impact of infection on sperm functional characteristics, and define the viral reservoir in the male reproductive tract. Five adult male rhesus monkeys were inoculated with 105 PFU of Asian-lineage ZIKV isolate PRVABC59, and two males were inoculated with the same dose of African-lineage ZIKV DAKAR41524. Viremia and viral RNA (vRNA) shedding in semen were monitored, and a cohort of animals were necropsied for tissue collection to assess tissue vRNA burden and histopathology. All animals exhibited viremia for limited periods (1-11 days); duration of shedding did not differ significantly between viral isolates. There were sporadic low levels of vRNA in the semen from some, but not all animals. Viral RNA levels in reproductive tract tissues were also modest and present in the epididymis in three of five cases, one case in the vas deferens, but not detected in testis, seminal vesicles or prostate. ZIKV infection did not impact semen motility parameters as assessed by computer-assisted sperm analysis. Despite some evidence of prolonged ZIKV RNA shedding in human semen and high tropism of ZIKV for male reproductive tract tissues in mice deficient in Type 1 interferon signaling, in the rhesus macaques assessed in this pilot study, we did not consistently find ZIKV RNA in the male reproductive tract.

Lights and Shadows of TORCH Infection Proteomics

Congenital abnormalities cause serious fetal consequences. The term TORCH is used to designate the most common perinatal infections, where: (T) refers to toxoplasmosis, (O) means "others" and includes syphilis, varicella-zoster, parvovirus B19, zika virus (ZIKV), and malaria among others, (R) refers to rubella, (C) relates to cytomegalovirus infection, and (H) to herpes simplex virus infections. Among the main abnormalities identified in neonates exposed to congenital infections are central nervous system (CNS) damage, microcephaly, hearing loss, and ophthalmological impairment, all requiring regular follow-up to monitor its progression. Protein changes such as mutations, post-translational modifications, abundance, structure, and function may indicate a pathological condition before the onset of the first symptoms, allowing early diagnosis and understanding of a particular disease or infection. The term "proteomics" is defined as the science that studies the proteome, which consists of the total protein content of a cell, tissue or organism in a given space and time, including post-translational modifications (PTMs) and interactions between proteins. Currently, quantitative bottom-up proteomic strategies allow rapid and high throughput characterization of complex biological mixtures. Investigating proteome modulation during host-pathogen interaction helps in elucidating the mechanisms of infection and in predicting disease progression. This "molecular battle" between host and pathogen is a key to identify drug targets and diagnostic markers. Here, we conducted a survey on proteomic techniques applied to congenital diseases classified in the terminology "TORCH", including toxoplasmosis, ZIKV, malaria, syphilis, human immunodeficiency virus (HIV), herpes simplex virus (HSV) and human cytomegalovirus (HCVM). We have highlighted proteins and/or protein complexes actively involved in the infection. Most of the proteomic studies reported have been performed in cell line models, and the evaluation of tissues (brain, muscle, and placenta) and biofluids (plasma, serum and urine) in animal models is still underexplored. Moreover, there are a plethora of studies focusing on the pathogen or the host without considering the triad mother-fetus-pathogen as a dynamic and interconnected system.

Sofosbuvir shows a protective effect against vertical transmission of Zika virus and the associated congenital syndrome in rhesus monkeys

The outbreaks of Zika virus (ZIKV) infection in Brazil, 2015-2016, were associated with severe congenital malformations. Our translational study aimed to test the efficacy of the antiviral agent sofosbuvir (SOF) against vertical transmission of ZIKV and the associated congenital syndrome (CZS), using a rhesus monkey model. Eight pregnant macaques were successfully infected during the organogenesis phase with a Brazilian ZIKV strain; five of them received SOF from two to fifteen days post-infection. Both groups of dams showed ZIKV-associated clinical signals, detectable ZIKV RNA in several specimens, specific anti-ZIKV IgM and IgG antibodies, and maternal neutralizing antibodies. However, malformations occurred only among non-treated dam offspring. Compared to non-treated animals, all SOF-treated dams had a shorter ZIKV viremia and four of five neonates had undetectable ZIKV RNA in blood and tissue samples. These results support further clinical evaluations aiming for the prevention of CZS.

Role of microglia in the dissemination of Zika virus from mother to fetal brain

Global Zika virus (ZIKV) outbreaks and their link to microcephaly have raised major public health concerns. However, the mechanism of maternal-fetal transmission remains largely unknown. In this study, we determined the role of yolk sac (YS) microglial progenitors in a mouse model of ZIKV vertical transmission. We found that embryonic (E) days 6.5-E8.5 were a critical window for ZIKV infection that resulted in fetal demise and microcephaly, and YS microglial progenitors were susceptible to ZIKV infection. Ablation of YS microglial progenitors significantly reduced the viral load in both the YS and the embryonic brain. Taken together, these results support the hypothesis that YS microglial progenitors serve as “Trojan horses,” contributing to ZIKV fetal brain dissemination and congenital brain defects.

ZIKV is more likely to cause fetal demise and brain malformations when the mother is infected at an early stage of pregnancy, which is the critical time window when a special type of immune cells called microglia appear in the YS and migrate to the fetal brain. YS-derived microglia are susceptible to ZIKV infection and can act as “Trojan horses” to bring ZIKV from the mother to the fetal brain.

Modeling mosquito-borne and sexual transmission of Zika virus in an enzootic host, the African green monkey

Mosquito-borne and sexual transmission of Zika virus (ZIKV), a TORCH pathogen, recently initiated a series of large epidemics throughout the Tropics. Animal models are necessary to determine transmission risk and study pathogenesis, as well screen antivirals and vaccine candidates. In this study, we modeled mosquito and sexual transmission of ZIKV in the African green monkey (AGM). Following subcutaneous, intravaginal or intrarectal inoculation of AGMs with ZIKV, we determined the transmission potential and infection dynamics of the virus. AGMs inoculated by all three transmission routes exhibited viremia and viral shedding followed by strong virus neutralizing antibody responses, in the absence of clinical illness. All four of the subcutaneously inoculated AGMs became infected (mean peak viremia: 2.9 log₁₀ PFU/mL, mean duration: 4.3 days) and vRNA was detected in their oral swabs, with infectious virus being detected in a subset of these specimens. Although all four of the intravaginally inoculated AGMs developed virus neutralizing antibody responses, only three had detectable viremia (mean peak viremia: 4.0 log₁₀ PFU/mL, mean duration: 3.0 days). These three AGMs also had vRNA and infectious virus detected in both oral and vaginal swabs. Two of the four intrarectally inoculated AGMs became infected (mean peak viremia: 3.8 log₁₀ PFU/mL, mean duration: 3.5 days). vRNA was detected in oral swabs collected from both of these infected AGMs, and infectious virus was detected in an oral swab from one of these AGMs. Notably, vRNA and infectious virus were detected in vaginal swabs collected from the infected female AGM (peak viral load: 7.5 log₁₀ copies/mL, peak titer: 3.8 log₁₀ PFU/mL, range of detection: 5–21 days post infection). Abnormal clinical chemistry and hematology results were detected and acute lymphadenopathy was observed in some AGMs. Infection dynamics in all three AGM ZIKV models are similar to those reported in the majority of human ZIKV infections. Our results indicate that the AGM can be used as a surrogate to model mosquito or sexual ZIKV transmission and infection. Furthermore, our results suggest that AGMs are likely involved in the enzootic maintenance and amplification cycle of ZIKV.

Zika virus (ZIKV) is primarily maintained in an enzootic cycle involving nonhuman primates and mosquitoes, with epizootics and epidemics occurring when the virus is introduced into naïve populations of nonhuman primates or humans, respectively. While, the primary transmission mechanism of the virus is by the bite on an infected mosquito, ZIKV can also be sexually transmitted. In an effort to develop novel animal models to study ZIKV disease, and to better understand the role of nonhuman primates as amplification and maintenance hosts of ZIKV in nature, we modeled mosquito-borne and sexual transmission of ZIKV in the enzootic host, the African green monkey (AGM). Infection dynamics and neutralizing antibody responses in all three AGM ZIKV models (subcutaneous, intravaginal and intrarectal) in the absence of clinical illness–recapitulated reported generalized human disease course. Furthermore, we detected prolonged shedding with high viral loads and infectious virus in the vaginal swabs collected from an infected female AGM inoculated intrarectally. Notably, these results support limited human clinical evidence that ZIKV transmission can occur during female-to-male vaginal sexual acts, and furthermore indicate the existence of ZIKV super-spreaders. Finally, our results indicate sexual transmission of ZIKV could occur among infected nonhuman primates (e.g. Chlorocebus spp.) in Africa and may serve as a secondary transmission and maintenance mechanism in the absence of mosquito-to-nonhuman primate transmission.

Maternal Zika Virus (ZIKV) Infection following Vaginal Inoculation with ZIKV-Infected Semen in Timed-Pregnant Olive Baboons

Zika virus (ZIKV) infection is now firmly linked to congenital Zika syndrome (CZS), including fetal microcephaly. While Aedes species of mosquito are the primary vector for ZIKV, sexual transmission of ZIKV is a significant route of infection. ZIKV has been documented in human, mouse, and nonhuman primate (NHP) semen. It is critical to establish NHP models of the vertical transfer of ZIKV that recapitulate human pathogenesis. We hypothesized that vaginal deposition of ZIKV-infected baboon semen would lead to maternal infection and vertical transfer in the olive baboon (Papio anubis). Epidemiological studies suggest an increased rate of CZS in the Americas compared to the original link to CZS in French Polynesia; therefore, we also compared the French Polynesian (FP) ZIKV isolate to the Puerto Rican (PR) isolate. Timed-pregnant baboons (n = 6) were inoculated via vaginal deposition of baboon semen containing 10⁶ focus-forming units (FFU) of ZIKV (n = 3 for FP isolate H/PF/2013; n = 3 for PR isolate PRVABC59) at midgestation (86 to 95 days of gestation [dG]; term, 183 dG) on day 0 (all dams) and then at 7-day intervals through 3 weeks. Maternal blood, saliva, and cervicovaginal wash (CVW) samples were obtained. Animals were euthanized at 28 days (n = 5) or 39 days (n = 1) after the initial inoculation, and maternal/fetal tissues were collected. Viremia was achieved in 3/3 FP ZIKV-infected dams and 2/3 PR ZIKV-infected dams. ZIKV RNA was detected in CVW samples of 5/6 dams. ZIKV RNA was detected in lymph nodes but not the ovaries, uterus, cervix, or vagina in FP isolate-infected dams. ZIKV RNA was detected in lymph nodes (3/3), uterus (2/3), and vagina (2/3) in PR isolate-infected dams. Placenta, amniotic fluid, and fetal tissues were ZIKV RNA negative in the FP isolate-infected dams, whereas 2/3 PR isolate-infected dam placentas were ZIKV RNA positive. We conclude that ZIKV-infected semen is a means of ZIKV transmission during pregnancy in primates. The PR isolate appeared more capable of widespread dissemination to tissues, including reproductive tissues and placenta, than the FP isolate.IMPORTANCE Zika virus remains a worldwide health threat, with outbreaks still occurring in the Americas. While mosquitos are the primary vector for the spread of the virus, sexual transmission of Zika virus is also a significant means of infection, especially in terms of passage from an infected to an uninfected partner. While sexual transmission has been documented in humans, and male-to-female transmission has been reported in mice, ours is the first study in nonhuman primates to demonstrate infection via vaginal deposition of Zika virus-infected semen. The latter is important since a recent publication indicated that human semen inhibited, in a laboratory setting, Zika virus infection of reproductive tissues. We also found that compared to the French Polynesian isolate, the Puerto Rican Zika virus isolate led to greater spread throughout the body, particularly in reproductive tissues. The American isolates of Zika virus appear to have acquired mutations that increase their efficacy.

Experimental Infection of Mid-Gestation Pregnant Female and Intact Male Sheep with Zika Virus

Zika virus (ZIKV) is an arbovirus that causes birth defects, persistent male infection, and sexual transmission in humans. The purpose of this study was to continue the development of an ovine ZIKV infection model; thus, two experiments were undertaken. In the first experiment, we built on previous pregnant sheep experiments by developing a mid-gestation model of ZIKV infection. Four pregnant sheep were challenged with ZIKV at 57–64 days gestation; two animals served as controls. After 13–15 days (corresponding with 70–79 days of gestation), one control and two infected animals were euthanized; the remaining animals were euthanized at 20–22 days post-infection (corresponding with 77–86 days of gestation). In the second experiment, six sexually mature, intact, male sheep were challenged with ZIKV and two animals served as controls. Infected animals were serially euthanized on days 2–6 and day 9 post-infection with the goal of isolating ZIKV from the male reproductive tract. In the mid-gestation study, virus was detected in maternal placenta and spleen, and in fetal organs, including the brains, spleens/liver, and umbilicus of infected fetuses. Fetuses from infected animals had visibly misshapen heads and morphometrics revealed significantly smaller head sizes in infected fetuses when compared to controls. Placental pathology was evident in infected dams. In the male experiment, ZIKV was detected in the spleen, liver, testes/epididymides, and accessory sex glands of infected animals. Results from both experiments indicate that mid-gestation ewes can be infected with ZIKV with subsequent disruption of fetal development and that intact male sheep are susceptible to ZIKV infection and viral dissemination and replication occurs in highly vascular tissues (including those of the male reproductive tract).

A neonatal nonhuman primate model of gestational Zika virus infection with evidence of microencephaly, seizures and cardiomyopathy

Zika virus infection during pregnancy is associated with miscarriage and with a broad spectrum of fetal and neonatal developmental abnormalities collectively known as congenital Zika syndrome (CZS). Symptomology of CZS includes malformations of the brain and skull, neurodevelopmental delay, seizures, joint contractures, hearing loss and visual impairment. Previous studies of Zika virus in pregnant rhesus macaques (Macaca mulatta) have described injury to the developing fetus and pregnancy loss, but neonatal outcomes following fetal Zika virus exposure have yet to be characterized in nonhuman primates. Herein we describe the presentation of rhesus macaque neonates with a spectrum of clinical outcomes, including one infant with CZS-like symptoms including cardiomyopathy, motor delay and seizure activity following maternal infection with Zika virus during the first trimester of pregnancy. Further characterization of this neonatal nonhuman primate model of gestational Zika virus infection will provide opportunities to evaluate the efficacy of pre- and postnatal therapeutics for gestational Zika virus infection and CZS.

Embryotoxic impact of Zika virus in a rhesus macaque in vitro implantation model†

Zika virus (ZIKV) infection is associated with adverse pregnancy outcomes in humans, and infection in the first trimester can lead to miscarriage and stillbirth. Vertical and sexual transmissions of ZIKV have been demonstrated, yet the impact of infection during the initial stages of pregnancy remains unexplored. Here we defined the impact of ZIKV on early embryonic and placental development with a rhesus macaque model. During in vitro fertilization (IVF), macaque gametes were inoculated with a physiologically relevant dose of 5.48log10 plaque-forming units (PFU) of Zika virus/H.sapiens-tc/PUR/2015/PRVABC59_v3c2. Exposure at fertilization did not alter blastocyst formation rates compared to controls. To determine the impact of ZIKV exposure at implantation, hatched blastocysts were incubated with 3.26log10, 4.26log10, or 5.26log10 PFU, or not exposed to ZIKV, followed by extended embryo culture for 10 days. ZIKV exposure negatively impacted attachment, growth, and survival in comparison to controls, with exposure to 5.26log10 PFU ZIKV resulting in embryonic degeneration by day 2. Embryonic secretion of pregnancy hormones was lower in ZIKV-exposed embryos. Increasing levels of infectious virus were detected in the culture media post-exposure, suggesting that the trophectoderm is susceptible to productive ZIKV infection. These results demonstrate that ZIKV exposure severely impacts the zona-free blastocyst, whereas exposure at the time of fertilization does not hinder blastocyst formation. Overall, early stages of pregnancy may be profoundly sensitive to infection and pregnancy loss, and the negative impact of ZIKV infection on pregnancy outcomes may be underestimated.

Zika Vaccine Development: Current Status

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

Using Macaques to Address Critical Questions in Zika Virus Research

Zika virus (ZIKV) and nonhuman primates have been inextricably linked since the virus was first discovered in a sentinel rhesus macaque in Uganda in 1947. Soon after ZIKV was epidemiologically associated with birth defects in Brazil late in 2015, researchers capitalized on the fact that rhesus macaques are commonly used to model viral immunity and pathogenesis, quickly establishing macaque models for ZIKV infection. Within months, the susceptibility of pregnant macaques to experimental ZIKV challenge and ZIKV-associated abnormalities in fetuses was confirmed. This review discusses key unanswered questions in ZIKV immunity and in the pathogenesis of thecongenital Zika virus syndrome. We focus on those questions that can be best addressed in pregnant nonhuman primates and lessons learned from developing macaque models for ZIKV amid an active epidemic.

Protective and Pathogenic Effects of Interferon Signaling During Pregnancy

Immune regulation at the maternal-fetal interface is complex due to conflicting immunological objectives: protection of the fetus from maternal pathogens and prevention of immune-mediated rejection of the semiallogeneic fetus and placenta. Interferon (IFN) signaling plays an important role in restricting congenital infections as well as in the physiology of healthy pregnancies. In this review, we discuss the antiviral and pathogenic effects of type I IFN (IFN-α, IFN-β), type II IFN (IFN-γ), and type III IFN (IFN-λ) during pregnancy, with an emphasis on mouse and non-human primate models of congenital Zika virus infection. In the context of these animal model systems, we examine the role of IFN signaling during healthy pregnancy. Finally, we review mechanisms by which dysregulated type I IFN responses contribute to poor pregnancy outcomes in humans with autoimmune disease, including interferonopathies and systemic lupus erythematosus.

Experimental Infection of Pregnant Female Sheep with Zika Virus During Early Gestation

Zika virus (ZIKV) is a vertically and sexually transmissible virus resulting in severe congenital malformation. The goal of this study was to develop an ovine model of ZIKV infection. Between 28–35 days gestation (DG), four pregnant animals were infected with two doses of 6 × 10⁶ PFU of ZIKV; four control animals received PBS. Animals were evaluated for 45 days (D) post-infection (PI) and necropsies were performed. Viral RNA was detected in infected ewe peripheral blood mononuclear cells (PBMC) during the first week PI; however, all fluids and tissues were negative upon culture. Anti-ZIKV IgM (1:400) and neutralizing antibodies were detected in all infected animals. Clinical disease, virus, or ZIKV antibodies were not detected in control ewes. After two weeks PI, fetal loss occurred in two infected animals, and at necropsy, three infected animals had placental petechiation and ecchymosis and one had hydramnion. Fetal morphometrics revealed smaller cranial circumference to crown-rump length ratios (p < 0.001) and relative brain weights (p = 0.038) in fetuses of infected animals compared with control fetuses. Immunophenotyping indicated an increase in B cells (p = 0.012) in infected sheep. Additionally, in vitro experiments using both adult and fetal cell lines demonstrated that ovine cells are highly permissive to ZIKV infection. In conclusion, ZIKV infection of pregnant sheep results in a change in fetal growth and gestational outcomes.

Primary infection with dengue or Zika virus does not affect the severity of heterologous secondary infection in macaques

Zika virus (ZIKV) and dengue virus (DENV) are genetically and antigenically related flaviviruses that now co-circulate in much of the tropical and subtropical world. The rapid emergence of ZIKV in the Americas in 2015 and 2016, and its recent associations with Guillain-Barré syndrome, birth defects, and fetal loss have led to the hypothesis that DENV infection induces cross-reactive antibodies that influence the severity of secondary ZIKV infections. It has also been proposed that pre-existing ZIKV immunity could affect DENV pathogenesis. We examined outcomes of secondary ZIKV infections in three rhesus and fifteen cynomolgus macaques, as well as secondary DENV-2 infections in three additional rhesus macaques up to a year post-primary ZIKV infection. Although cross-binding antibodies were detected prior to secondary infection for all animals and cross-neutralizing antibodies were detected for some animals, previous DENV or ZIKV infection had no apparent effect on the clinical course of heterotypic secondary infections in these animals. All animals had asymptomatic infections and, when compared to controls, did not have significantly perturbed hematological parameters. Rhesus macaques infected with DENV-2 approximately one year after primary ZIKV infection had higher vRNA loads in plasma when compared with serum vRNA loads from ZIKV-naive animals infected with DENV-2, but a differential effect of sample type could not be ruled out. In cynomolgus macaques, the serotype of primary DENV infection did not affect the outcome of secondary ZIKV infection.

Pre-existing immunity to one of the four DENV serotypes is known to increase the risk of severe disease upon secondary infection with a different serotype. Due to the antigenic similarities between ZIKV and DENV, it has been proposed that these viruses could interact in a similar fashion. Data from in vitro experiments and murine models suggests that pre-existing immunity to one virus could either enhance or protect against infection with the other. These somewhat contradictory findings highlight the need for immune competent animal models for understanding the role of cross-reactive antibodies in flavivirus pathogenesis. We examined secondary ZIKV or DENV infections in rhesus and cynomolgus macaques that had previously been infected with the other virus. We assessed the outcomes of secondary ZIKV or DENV infections by quantifying vRNA loads, clinical and laboratory parameters, body temperature, and weight for each cohort of animals and compared them with control animals. These comparisons demonstrated that within a year of primary infection, secondary infections with either ZIKV or DENV were similar to primary infections and were not associated with enhancement or reduction in severity of disease based on the outcomes that we assessed.

In-depth characterization of congenital Zika syndrome in immunocompetent mice: Antibody-dependent enhancement and an antiviral peptide therapy

BACKGROUND

Zika virus (ZIKV) infection during pregnancy may cause major congenital defects, including microcephaly, ocular, articular and muscle abnormalities, which are collectively defined as Congenital Zika Syndrome. Here, we performed an in-depth characterization of the effects of congenital ZIKV infection (CZI) in immunocompetent mice.

METHODS

Pregnant dams were inoculated with ZIKV on embryonic day 5.5 in the presence or absence of a sub-neutralizing dose of a pan-flavivirus monoclonal antibody (4G2) to evaluate the potential role of antibody-dependent enhancement phenomenon (ADE) during short and long outcomes of CZI.

FINDINGS

ZIKV infection induced maternal immune activation (MIA), which was associated with occurrence of foetal abnormalities and death. Therapeutic administration of AH-D antiviral peptide during the early stages of pregnancy prevented ZIKV replication and death of offspring. In the post-natal period, CZI was associated with a decrease in whole brain volume, ophthalmologic abnormalities, changes in testicular morphology, and disruption in bone microarchitecture. Some alterations were enhanced in the presence of 4G2 antibody.

INTERPRETATION

Our results reveal that early maternal ZIKV infection causes several birth defects in immunocompetent mice, which can be potentiated by ADE phenomenon and are associated with MIA. Additionally, antiviral treatment with AH-D peptide may be beneficial during early maternal ZIKV infection. FUND: This work was supported by the Brazilian National Science Council (CNPq, Brazil), Minas Gerais Foundation for Science (FAPEMIG), Funding Authority for Studies and Projects (FINEP), Coordination of Superior Level Staff Improvement (CAPES), National Research Foundation of Singapore and Centre for Precision Biology at Nanyang Technological University.

Zika Virus Infects Trabecular Meshwork and Causes Trabeculitis and Glaucomatous Pathology in Mouse Eyes

Zika virus (ZIKV) infection during pregnancy leads to devastating fetal outcomes, including neurological (microcephaly) and ocular pathologies such as retinal lesions, optic nerve abnormalities, chorioretinal atrophy, and congenital glaucoma. Only clinical case reports have linked ZIKV infection to causing glaucoma, a major blinding eye disease. In the present study, we have investigated the role of ZIKV in glaucoma pathophysiology using in vitro and in vivo experimental models. We showed that human primary trabecular meshwork (Pr. TM) cells, as well as a human GTM3 cell line, were permissive to ZIKV infection. ZIKV induced the transcription of various genes expressing pattern recognition receptors (TLR2, TLR3, and RIG-I), cytokines/chemokines (TNF-α, IL-1β, CCL5, and CXCL10), interferons (IFN-α2, IFN-β1, and IFN-γ), and interferon-stimulated genes (ISG15 and OAS2) in Pr. TM cells. ZIKV infection in IFNAR1-/- and wild-type (WT) mouse eyes resulted in increased intraocular pressure (IOP) and the development of chorioretinal atrophy. Anterior chamber (AC) inoculation of ZIKV caused infectivity in iridocorneal angle and TM, leading to the death of TM cells in the mouse eyes. Moreover, anterior segment tissue of infected eyes exhibited increased expression of inflammatory mediators and interferons. Furthermore, ZIKV infection in IFNAR1-/- mice resulted in retinal ganglion cell (RGC) death and loss, coinciding with optic nerve infectivity and disruption of anterograde axonal transport. Because of similarity in glaucomatous pathologies in our study and other experimental glaucoma models, ZIKV infection can be used to study infectious triggers of glaucoma, currently an understudied area of investigation.IMPORTANCE Ocular complications due to ZIKV infection remains a major public health concern because of their ability to cause visual impairment or blindness. Most of the previous studies have shown ZIKV-induced ocular pathology in the posterior segment (i.e., retina) of the eye. However, some recent clinical reports from affected countries highlighted the importance of ZIKV in affecting the anterior segment of the eye and causing congenital glaucoma. Because glaucoma is the second leading cause of blindness worldwide, it is imperative to study ZIKV infection in causing glaucoma to identify potential targets for therapeutic intervention. In this study, we discovered that ZIKV permissively infects human TM cells and evokes inflammatory responses causing trabeculitis. Using a mouse model, we demonstrated that ZIKV infection resulted in higher IOP, increased RGC loss, and optic nerve abnormalities, the classical hallmarks of glaucoma. Collectively, our study provides new insights into ocular ZIKV infection resulting in glaucomatous pathology.

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

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

Zika virus infection at mid-gestation results in fetal cerebral cortical injury and fetal death in the olive baboon

Zika virus (ZIKV) infection during pregnancy in humans is associated with an increased incidence of congenital anomalies including microcephaly as well as fetal death and miscarriage and collectively has been referred to as Congenital Zika Syndrome (CZS). Animal models for ZIKV infection in pregnancy have been developed including mice and non-human primates (NHPs). In macaques, fetal CZS outcomes from maternal ZIKV infection range from none to significant. In the present study we develop the olive baboon (Papio anubis), as a model for vertical transfer of ZIKV during pregnancy. Four mid-gestation, timed-pregnant baboons were inoculated with the French Polynesian ZIKV isolate (10⁴ ffu). This study specifically focused on the acute phase of vertical transfer. Dams were terminated at 7 days post infection (dpi; n = 1), 14 dpi (n = 2) and 21 dpi (n = 1). All dams exhibited mild to moderate rash and conjunctivitis. Viremia peaked at 5–7 dpi with only one of three dams remaining mildly viremic at 14 dpi. An anti-ZIKV IgM response was observed by 14 dpi in all three dams studied to this stage, and two dams developed a neutralizing IgG response by either 14 dpi or 21 dpi, the latter included transfer of the IgG to the fetus (cord blood). A systemic inflammatory response (increased IL2, IL6, IL7, IL15, IL16) was observed in three of four dams. Vertical transfer of ZIKV to the placenta was observed in three pregnancies (n = 2 at 14 dpi and n = 1 at 21 dpi) and ZIKV was detected in fetal tissues in two pregnancies: one associated with fetal death at ~14 dpi, and the other in a viable fetus at 21 dpi. ZIKV RNA was detected in the fetal cerebral cortex and other tissues of both of these fetuses. In the fetus studied at 21 dpi with vertical transfer of virus to the CNS, the frontal cerebral cortex exhibited notable defects in radial glia, radial glial fibers, disorganized migration of immature neurons to the cortical layers, and signs of pathology in immature oligodendrocytes. In addition, indices of pronounced neuroinflammation were observed including astrogliosis, increased microglia and IL6 expression. Of interest, in one fetus examined at 14 dpi without detection of ZIKV RNA in brain and other fetal tissues, increased neuroinflammation (IL6 and microglia) was observed in the cortex. Although the placenta of the 14 dpi dam with fetal death showed considerable pathology, only minor pathology was noted in the other three placentas. ZIKV was detected immunohistochemically in two placentas (14 dpi) and one placenta at 21 dpi but not at 7 dpi. This is the first study to examine the early events of vertical transfer of ZIKV in a NHP infected at mid-gestation. The baboon thus represents an additional NHP as a model for ZIKV induced brain pathologies to contrast and compare to humans as well as other NHPs.

Zika virus is endemic in the Americas, primarily spread through mosquitos and sexual contact. Zika virus infection during pregnancy in women is associated with a variety of fetal pathologies now referred to as Congenital Zika Syndrome (CZS), with the most severe pathology being fetal microcephaly. Developing model organisms that faithfully recreate Zika infection in humans is critical for future development of treatments and preventions. In our present study, we infected Olive baboons at mid-gestation with Zika virus and studied the acute period of viremia and transfer of Zika virus to the fetus during the first three weeks after infection to better understand the timing and mechanisms of transfer of ZIKV across the placenta, leading to CZS. We observed Zika virus transfer to fetuses resulting in fetal death in one pregnancy and in a second pregnancy, significant damage to the frontal cortex of the fetal brain at a critical period of neurodevelopment in primates. Thus, the baboon provides a promising new non-human primate model to further compare and contrast the consequences of Zika virus infection in pregnancy to humans and other non-human primates.

Zika virus induces strong inflammatory responses and impairs homeostasis and function of the human retinal pigment epithelium

BACKGROUND

Zika virus (ZIKV) has recently re-emerged as a pathogenic agent with epidemic capacities as was well illustrated in South America. Because of the extent of this health crisis, a number of more serious symptoms have become associated with ZIKV infection than what was initially described. In particular, neuronal and ocular disorders have been characterized, both in infants and in adults. Notably, the macula and the retina can be strongly affected by ZIKV, possibly by a direct effect of the virus. This is supported by the detection of replicative and infectious virus in lachrimal fluid in human patients and mouse models.

METHODS

Here, we used an innovative, state-of-the-art iPSC-derived human retinal pigment epithelium (RPE) model to study ZIKV retinal impairment.

FINDINGS

We showed that the human RPE is highly susceptible to ZIKV infection and that a ZIKV African strain was more virulent and led to a more potent epithelium disruption and stronger anti-viral response than an Asian strain, suggesting lineage differences. Moreover, ZIKV infection led to impaired membrane dynamics involved in endocytosis, organelle biogenesis and potentially secretion, key mechanisms of RPE homeostasis and function.

INTERPRETATION

Taken together, our results suggest that ZIKV has a highly efficient ocular tropism, which creates a strong inflammatory environment that could have acute or chronic adverse effects. FUND: This work was funded by Retina France, REACTing and La Région Languedoc-Roussillon.

Modeling Zika Virus-Associated Birth Defects in Nonhuman Primates

In utero infection with Zika virus (ZIKV) during pregnancy can lead to the development of birth defects and postnatal deficits. A nonhuman primate (NHP) model of congenital ZIKV infection can help fill the gaps in knowledge where tissue studies are required to define viral pathogenesis and identify targets for therapeutic intervention. This model system has already identified critical features of ZIKV pathogenesis in congenital infection. Before translating these NHP studies to human clinical trials, we must understand the similarities and differences between human and NHP fetal immune system development, neural development, and infant assessment tools. Because of the overall similarity between fetal and infant development in humans and NHPs, this NHP model can complement human clinical trials by defining immune correlates of protection and evaluating therapeutic interventions.

ZIKV Demonstrates Minimal Pathologic Effects and Mosquito Infectivity in Viremic Cynomolgus Macaques

To evaluate the effects of ZIKV infection on non-human primates (NHPs), as well as to investigate whether these NHPs develop sufficient viremia to infect the major urban vector mosquito, Aedes aegypti, four cynomolgus macaques (Macaca fascicularis) were subcutaneously infected with 5.0 log₁₀ focus-forming units (FFU) of DNA clone-derived ZIKV strain FSS13025 (Asian lineage, Cambodia, 2010). Following infection, the animals were sampled (blood, urine, tears, and saliva), underwent daily health monitoring, and were exposed to Ae. aegypti at specified time points. All four animals developed viremia, which peaked 3⁻4 days post-infection at a maximum value of 6.9 log₁₀ genome copies/mL. No virus was detected in urine, tears, or saliva. Infection by ZIKV caused minimal overt disease: serum biochemistry and CBC values largely fell within the normal ranges, and cytokine elevations were minimal. Strikingly, the minimally colonized population of Ae. aegypti exposed to viremic animals demonstrated a maximum infection rate of 26% during peak viremia, with two of the four macaques failing to infect a single mosquito at any time point. These data indicate that cynomolgus macaques may be an effective model for ZIKV infection of humans and highlights the relative refractoriness of Ae. aegypti for ZIKV infection at the levels of viremia observed.

Antibody responses to Zika virus proteins in pregnant and non-pregnant macaques

The specificity of the antibody response against Zika virus (ZIKV) is not well-characterized. This is due, in part, to the antigenic similarity between ZIKV and closely related dengue virus (DENV) serotypes. Since these and other similar viruses co-circulate, are spread by the same mosquito species, and can cause similar acute clinical syndromes, it is difficult to disentangle ZIKV-specific antibody responses from responses to closely-related arboviruses in humans. Here we use high-density peptide microarrays to profile anti-ZIKV antibody reactivity in pregnant and non-pregnant macaque monkeys with known exposure histories and compare these results to reactivity following DENV infection. We also compare cross-reactive binding of ZIKV-immune sera to the full proteomes of 28 arboviruses. We independently confirm a purported ZIKV-specific IgG antibody response targeting ZIKV nonstructural protein 2B (NS2B) that was recently reported in ZIKV-infected people and we show that antibody reactivity in pregnant animals can be detected as late as 127 days post-infection (dpi). However, we also show that these responses wane over time, sometimes rapidly, and in one case the response was elicited following DENV infection in a previously ZIKV-exposed animal. These results suggest epidemiologic studies assessing seroprevalence of ZIKV immunity using linear epitope-based strategies will remain challenging to interpret due to susceptibility to false positive results. However, the method used here demonstrates the potential for rapid profiling of proteome-wide antibody responses to a myriad of neglected diseases simultaneously and may be especially useful for distinguishing antibody reactivity among closely related pathogens.

Animal Models of Zika Virus Infection during Pregnancy

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

Mathematical modeling of within-host Zika virus dynamics

Recent Zika virus outbreaks have been associated with severe outcomes, especially during pregnancy. A great deal of effort has been put toward understanding this virus, particularly the immune mechanisms responsible for rapid viral control in the majority of infections. Identifying and understanding the key mechanisms of immune control will provide the foundation for the development of effective vaccines and antiviral therapy. Here, we outline a mathematical modeling approach for analyzing the within-host dynamics of Zika virus, and we describe how these models can be used to understand key aspects of the viral life cycle and to predict antiviral efficacy.

Adenoviral vector type 26 encoding Zika virus (ZIKV) M-Env antigen induces humoral and cellular immune responses and protects mice and nonhuman primates against ZIKV challenge

In 2015, there was a large outbreak of Zika virus (ZIKV) in Brazil. Despite its relatively mild impact on healthy adults, ZIKV infection during pregnancy has been associated with severe birth defects. Currently, there is no ZIKV vaccine available, but several vaccine candidates based on the ZIKV membrane (M) and envelope (Env) structural proteins showed promising results in preclinical and clinical studies. Here, the immunogenicity and protective efficacy of a non-replicating adenoviral vector type 26 (Ad26) that encodes the ZIKV M-Env antigens (Ad26.ZIKV.M-Env) was evaluated in mice and non-human primates (NHP). Ad26.ZIKV.M-Env induced strong and durable cellular and humoral immune responses in preclinical models. Humoral responses were characterized by Env-binding and ZIKV neutralizing antibody responses while cellular responses were characterized by ZIKV reactive CD4+ and CD8+ T cells. Importantly, a single immunization with a very low dose of 4x107 vp of Ad26.ZIKV.M-Env protected mice from ZIKV challenge. In NHP, a single immunization with a typical human dose of 1x1011 vp of Ad26.ZIKV.M-Env also induced Env-binding and ZIKV neutralizing antibodies and Env and M specific cellular immune responses that associated with complete protection against viremia from ZIKV challenge as measured in plasma and other body fluids. Together these data provide the rationale to progress the Ad26.ZIKV.M-Env candidate vaccine to clinical testing.