Postnatal Zika virus infection of nonhuman primate infants born to mothers infected with homologous Brazilian Zika virus

Prenatal Zika virus infection has sex-specific effects on infant physical development and mother-infant social interactions

There is enormous variation in the extent to which fetal Zika virus (fZIKV) infection affects the developing brain. Despite the neural consequences of fZIKV infection observed in people and animal models, many open questions about the relationship between infection dynamics and fetal and infant development remain. To further understand how ZIKV affects the developing nervous system and the behavioral consequences of prenatal infection, we adopted a nonhuman primate model of fZIKV infection in which we inoculated pregnant rhesus macaques and their fetuses with ZIKV in the early second trimester of fetal development. We then tracked their health across gestation and characterized infant development across the first month of life. ZIKV-infected pregnant mothers had long periods of viremia and mild changes to their hematological profiles. ZIKV RNA concentrations, an indicator of infection magnitude, were higher in mothers whose fetuses were male, and the magnitude of ZIKV RNA in the mothers' plasma or amniotic fluid predicted infant outcomes. The magnitude of ZIKV RNA was negatively associated with infant growth across the first month of life, affecting males' growth more than females' growth, although for most metrics, both males and females evidenced slower growth rates as compared with control animals whose mothers were not ZIKV inoculated. Compared with control infants, fZIKV infants also spent more time with their mothers during the first month of life, a social behavior difference that may have long-lasting consequences on psychosocial development during childhood.

Arthropod-Borne Flaviviruses in Pregnancy

Flaviviruses are a diverse group of enveloped RNA viruses that cause significant clinical manifestations in the pregnancy and postpartum periods. This review highlights the epidemiology, pathophysiology, clinical features, diagnosis, and prevention of the key arthropod-borne flaviviruses of concern in pregnancy and the neonatal period-Zika, Dengue, Japanese encephalitis, West Nile, and Yellow fever viruses. Increased disease severity during pregnancy, risk of congenital malformations, and manifestations of postnatal infection vary widely amongst this virus family and may be quite marked. Laboratory confirmation of infection is complex, especially due to the reliance on serology for which flavivirus cross-reactivity challenges diagnostic specificity. As such, a thorough clinical history including relevant geographic exposures and prior vaccinations is paramount for accurate diagnosis. Novel vaccines are eagerly anticipated to ameliorate the impact of these flaviviruses, particularly neuroinvasive disease manifestations and congenital infection, with consideration of vaccine safety in pregnant women and children pivotal. Moving forward, the geographical spread of flaviviruses, as for other zoonoses, will be heavily influenced by climate change due to the potential expansion of vector and reservoir host habitats. Ongoing 'One Health' engagement across the human-animal-environment interface is critical to detect and responding to emergent flavivirus epidemics.

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.

Nonhuman primates exposed to Zika virus in utero are not protected against reinfection at 1 year postpartum

There is limited information about the impact of Zika virus (ZIKV) exposure in utero on the anti-ZIKV immune responses of offspring. We infected six rhesus macaque dams with ZIKV early or late in pregnancy and studied four of their offspring over the course of a year postpartum. Despite evidence of ZIKV exposure in utero, we observed no structural brain abnormalities in the offspring. We detected infant-derived ZIKV-specific immunoglobulin A antibody responses and T cell memory responses during the first year postpartum in the two offspring born to dams infected with ZIKV early in pregnancy. Critically, although the infants had acquired some immunological memory of ZIKV, it was not sufficient to protect them against reinfection with ZIKV at 1 year postpartum. The four offspring reexposed to ZIKV at 1 year postpartum all survived but exhibited acute viremia and viral tropism to lymphoid tissues; three of four reexposed offspring exhibited spinal cord pathology. These data suggest that macaque infants born to dams infected with ZIKV during pregnancy remain susceptible to postnatal infection and consequent neuropathology.

Serosurvey of Nonhuman Primates in Costa Rica at the Human-Wildlife Interface Reveals High Exposure to Flaviviruses

Simple Summary

The presence of flavivirus-specific antibodies in neotropical non-human primates (NPs) (i.e., dengue virus) is well known. However, it is unclear if dengue virus or other flaviviruses could be maintained in sylvatic cycles. We detected the presence of antibodies against dengue virus (DENV-1, DENV-2), Saint Louis encephalitis virus (SLEV), West Nile virus (WNV), and several undetermined flaviviruses in NPs in Costa Rica. Our work suggests continuous exposure of NPs to several flaviviruses in Costa Rica. These findings open the question of whether bidirectional transmission between humans and non-human primates can occur due to human encroachment into NP habitats, the movement of NP into urban settings, or bridging vectors.

Abstract

Arthropod-borne viruses belonging to the flavivirus genus possess an enormous relevance in public health. Neotropical non-human primates (NPs) have been proposed to be susceptible to flavivirus infections due to their arboreal and diurnal habits, their genetic similarity to humans, and their relative closeness to humans. However, the only known flavivirus in the American continent maintained by sylvatic cycles involving NPs is yellow fever virus (YFV), and NPs’ role as potential hosts of other flaviviruses is still unknown. Here, we examined flavivirus exposure in 86 serum samples including 83.7% samples from free-range and 16.3% from captive NPs living in flavivirus-endemic regions of Costa Rica. Serum samples were opportunistically collected throughout Costa Rica in 2000–2015. We used a highly specific micro-plaque reduction neutralization test (micro-PRNT) to determine the presence of antibodies against YFV, dengue virus 1–4 (DENV), Zika virus, West Nile virus (WNV), and Saint Louis encephalitis virus (SLEV). We found evidence of seropositive NPs with homotypic reactivity to SLEV 11.6% (10/86), DENV 10.5% (9/86), and WNV 2.3% (2/86). Heterotypic reactivity was determined in 3.5% (3/86) of individuals against DENV, 1.2% (1/86) against SLEV, and 1.2% (1/86) against WNV. We found that 13.9% (12/86) of NPs were positive for an undetermined flavivirus species. No antibodies against DENV-3, DENV-4, YFV, or ZIKV were found. This work provides compelling serological evidence of flavivirus exposure in Costa Rican NPs, in particular to DENV, SLEV, and WNV. The range of years of sampling and the region from where positives were detected coincide with those in which peaks of DENV in human populations were registered, suggesting bidirectional exposure due to human–wildlife contact or bridging vectors. Our work suggests the continuous exposure of wildlife populations to various flaviviruses of public health importance and underscores the necessity of further surveillance of flaviviruses at the human–wildlife interface in Central America.

Persistence of Anti-ZIKV-IgG over Time Is Not a Useful Congenital Infection Marker in Infants Born to ZIKV-Infected Mothers: The NATZIG Cohort

Confirming ZIKV congenital infection is challenging because viral RNA is infrequently detected. We compared the presence of anti-ZIKV-IgM and the persistence of anti-ZIKV-IgG antibodies over 18 months in two cohorts of infants born to ZIKV-infected mothers: Cohort one: 30 infants with typical microcephaly or major brain abnormalities (Congenital Zika Syndrome-CZS); Cohort two: 123 asymptomatic infants. Serum samples obtained within 6 months of age were tested for anti-ZIKV-IgM. Anti-ZIKV-IgG was quantified in sequential samples collected at birth, 3-6 weeks, 3, 6, 12, and 18 months. ZIKV-RNA was never detected postnatally. Anti-ZIKV-IgM antibodies were detected at least once in 15/25 (60.0%; 95%CI: 38.7-78.9) infants with CZS and in 2/115 (1.7%; 95%CI: 0.2-6.1) asymptomatic infants. Although anti-ZIKV-IgG was always positive within 3-6 weeks of age, IgG levels decreased similarly over time in both cohorts. IgG levels decreased similarly in ZIKV-IgM-positive and ZIKV-IgM-negative CZS infants. Differently from other congenital infections, IgM would fail to diagnose 40% of severely symptomatic infants, and the persistence of IgG is not a useful marker for discriminating congenital infection among infants exposed to maternal ZIKV infection.

Zika virus infection during pregnancy protects against secondary infection in the absence of CD8+ cells

While T cell immunity is an important component of the immune response to Zika virus (ZIKV) infection generally, the efficacy of these responses during pregnancy remains unknown. Here, we tested the capacity of CD8 lymphocytes to protect from secondary challenge in four macaques, two of which were depleted of CD8⁺ cells prior to rechallenge with a heterologous ZIKV isolate. The initial challenge during pregnancy produced transcriptional signatures suggesting complex patterns of immune modulation as well as neutralizing antibodies that persisted until rechallenge, which all animals efficiently controlled, demonstrating that the primary infection conferred adequate protection. The secondary challenge promoted activation of innate and adaptive immune cells, possibly suggesting a brief period of infection prior to clearance. These data confirm that ZIKV infection during pregnancy induces sufficient immunity to protect from a secondary challenge and suggest that this protection is not dependent on CD8 T cells.

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Zika infection during pregnancy provides protection from secondary infection.

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CD8 T cell responses are not needed for protection from secondary infection.

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Zika infection during pregnancy results in immunomodulatory transcriptional signatures but little IFN response.

Pre-existing Immunity to Japanese Encephalitis Virus Alters CD4 T Cell Responses to Zika Virus Inactivated Vaccine

The epidemic spread of Zika virus (ZIKV), associated with devastating neurologic syndromes, has driven the development of multiple ZIKV vaccines candidates. An effective vaccine should induce ZIKV-specific T cell responses, which are shown to improve the establishment of humoral immunity and contribute to viral clearance. Here we investigated how previous immunization against Japanese encephalitis virus (JEV) and yellow fever virus (YFV) influences T cell responses elicited by a Zika purified-inactivated virus (ZPIV) vaccine. We demonstrate that three doses of ZPIV vaccine elicited robust CD4 T cell responses to ZIKV structural proteins, while ZIKV-specific CD4 T cells in pre-immunized individuals with JEV vaccine, but not YFV vaccine, were more durable and directed predominantly toward conserved epitopes, which elicited Th1 and Th2 cytokine production. In addition, T cell receptor repertoire analysis revealed preferential expansion of cross-reactive clonotypes between JEV and ZIKV, suggesting that pre-existing immunity against JEV may prime the establishment of stronger CD4 T cell responses to ZPIV vaccination. These CD4 T cell responses correlated with titers of ZIKV-neutralizing antibodies in the JEV pre-vaccinated group, but not in flavivirus-naïve or YFV pre-vaccinated individuals, suggesting a stronger contribution of CD4 T cells in the generation of neutralizing antibodies in the context of JEV-ZIKV cross-reactivity.

Transcriptional signatures of Zika virus infection in astrocytes

Astrocytes are an early and important target of Zika virus (ZIKV) infection in the developing brain, but the impacts of infection on astrocyte function remain controversial. Given that nonhuman primate (NHP) models of ZIKV infection replicate aspects of neurologic disease seen in human infections, we cultured primary astrocytes from the brain tissue of infant rhesus macaques and then infected the cells with Asian or African lineage ZIKV to identify transcriptional patterns associated with infection in these cells. The African lineage virus appeared to have greater infectivity and promote stronger antiviral signaling, but infection by either strain ultimately produced typical virus response patterns. Both viruses induced hypoxic stress, but the Asian lineage strain additionally had an effect on metabolic and lipid biosynthesis pathways. Together, these findings describe an NHP astrocyte model that may be used to assess transcriptional signatures following ZIKV infection.

Clinical and Preclinical Evidence for Adverse Neurodevelopment after Postnatal Zika Virus Infection

Although the Zika virus (ZIKV) typically causes mild or no symptoms in adults, during the 2015−2016 outbreak, ZIKV infection in pregnancy resulted in a spectrum of diseases in infants, including birth defects and neurodevelopmental disorders identified in childhood. While intense clinical and basic science research has focused on the neurodevelopmental outcomes of prenatal ZIKV infection, less is known about the consequences of infection during early life. Considering the neurotropism of ZIKV and the rapidly-developing postnatal brain, it is important to understand how infection during infancy may disrupt neurodevelopment. This paper reviews the current knowledge regarding early postnatal ZIKV infection. Emerging clinical evidence supports the hypothesis that ZIKV infection during infancy can result in negative neurologic consequences. However, clinical data regarding postnatal ZIKV infection in children are limited; as such, animal models play an important role in understanding the potential complications of ZIKV infection related to the vulnerable developing brain. Preclinical data provide insight into the potential behavioral, cognitive, and motor domains that clinical studies should examine in pediatric populations exposed to ZIKV during infancy.

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.