A single-dose live-attenuated vaccine prevents Zika virus pregnancy transmission and testis damage

Zika Virus in the Male Reproductive Tract

Arthropod-borne viruses (arboviruses) are resurging across the globe. Zika virus (ZIKV) has caused significant concern in recent years because it can lead to congenital malformations in babies and Guillain-Barré syndrome in adults. Unlike other arboviruses, ZIKV can be sexually transmitted and may persist in the male reproductive tract. There is limited information regarding the impact of ZIKV on male reproductive health and fertility. Understanding the mechanisms that underlie persistent ZIKV infections in men is critical to developing effective vaccines and therapies. Mouse and macaque models have begun to unravel the pathogenesis of ZIKV infection in the male reproductive tract, with the testes and prostate gland implicated as potential reservoirs for persistent ZIKV infection. Here, we summarize current knowledge regarding the pathogenesis of ZIKV in the male reproductive tract, the development of animal models to study ZIKV infection at this site, and prospects for vaccines and therapeutics against persistent ZIKV infection.

Cellular and Humoral Immunity Protect against Vaginal Zika Virus Infection in Mice

Zika virus (ZIKV), which can cause devastating disease in fetuses of infected pregnant women, can be transmitted by mosquito inoculation and sexual routes. Little is known about immune protection against sexually transmitted ZIKV. In this study, we show that previous infection through intravaginal or subcutaneous routes with a contemporary Brazilian strain of ZIKV can protect against subsequent intravaginal challenge with a homologous strain. Both routes of inoculation induced high titers of ZIKV-specific and neutralizing antibody in serum and the vaginal lumen. Virus-specific T cells were recruited to and retained in the female reproductive tract after intravaginal and subcutaneous ZIKV infection. Studies in mice with genetic or acquired deficiencies in B and/or T cells demonstrated that both lymphocyte populations redundantly protect against intravaginal challenge in ZIKV-immune animals. Passive transfer of ZIKV-immune IgG or T cells significantly limited intravaginal infection of naive mice, although antibody more effectively prevented dissemination throughout the reproductive tract. Collectively, our experiments begin to establish the immune correlates of protection against intravaginal ZIKV infection, which should inform vaccination strategies in nonpregnant and pregnant women.IMPORTANCE The recent ZIKV epidemic resulted in devastating outcomes in fetuses and may affect reproductive health. Unlike other flaviviruses, ZIKV can be spread by sexual contact as well as a mosquito vector. While previous studies have identified correlates of protection for mosquito-mediated infection, few have focused on immunity against sexual transmission. As exposure to ZIKV via mosquito bite has likely occurred to many living in areas where ZIKV is endemic, our study addresses whether this route of infection can protect against subsequent sexual exposure. We demonstrate that subcutaneous ZIKV infection can protect against subsequent vaginal infection by generating both local antiviral T cell and antibody responses. Our research begins to define the immune correlates of protection for ZIKV infection in the vagina and provides a foundation for testing ZIKV vaccines against sexual transmission.

A systematic approach to the development of a safe live attenuated Zika vaccine

Zika virus (ZIKV) is a flavivirus that can cause congenital disease and requires development of an effective long-term preventative strategy. A replicative ZIKV vaccine with properties similar to the yellow fever 17D (YF17D) live-attenuated vaccine (LAV) would be advantageous, as a single dose of YF17D produces lifelong immunity. However, a replicative ZIKV vaccine must also be safe from causing persistent organ infections. Here we report an approach to ZIKV LAV development. We identify a ZIKV variant that produces small plaques due to interferon (IFN)-restricted viral propagation and displays attenuated infection of endothelial cells. We show that these properties collectively reduce the risk of organ infections and vertical transmission in a mouse model but remain sufficiently immunogenic to prevent wild-type ZIKV infection. Our findings suggest a strategy for the development of a safe but efficacious ZIKV LAV.

Development of a chimeric Zika vaccine using a licensed live-attenuated flavivirus vaccine as backbone

The global spread of Zika virus (ZIKV) and its unexpected association with congenital defects necessitates the rapid development of a safe and effective vaccine. Here we report the development and characterization of a recombinant chimeric ZIKV vaccine candidate (termed ChinZIKV) that expresses the prM-E proteins of ZIKV using the licensed Japanese encephalitis live-attenuated vaccine SA14-14-2 as the genetic backbone. ChinZIKV retains its replication activity and genetic stability in vitro, while exhibiting an attenuation phenotype in multiple animal models. Remarkably, immunization of mice and rhesus macaques with a single dose of ChinZIKV elicits robust and long-lasting immune responses, and confers complete protection against ZIKV challenge. Significantly, female mice immunized with ChinZIKV are protected against placental and fetal damage upon ZIKV challenge during pregnancy. Overall, our study provides an alternative vaccine platform in response to the ZIKV emergency, and the safety, immunogenicity, and protection profiles of ChinZIKV warrant further clinical development.

Prevention and Control Strategies to Counter Zika Virus, a Special Focus on Intervention Approaches against Vector Mosquitoes-Current Updates

Zika virus (ZIKV) is the most recent intruder that acquired the status of global threat creating panic and frightening situation to public owing to its rapid spread, attaining higher virulence and causing complex clinical manifestations including microcephaly in newborns and Guillain Barré Syndrome. Alike other flaviviruses, the principal mode of ZIKV transmission is by mosquitoes. Advances in research have provided reliable diagnostics for detecting ZIKV infection, while several drug/therapeutic targets and vaccine candidates have been identified recently. Despite these progresses, currently there is neither any effective drug nor any vaccine available against ZIKV. Under such circumstances and to tackle the problem at large, control measures of which mosquito population control need to be strengthened following appropriate mechanical, chemical, biological and genetic control measures. Apart from this, several other known modes of ZIKV transmission which have gained importance in recent past such as intrauterine, sexual intercourse, and blood-borne spread need to be checked and kept under control by adopting appropriate precautions and utmost care during sexual intercourse, blood transfusion and organ transplantation. The virus inactivation by pasteurization, detergents, chemicals, and filtration can effectively reduce viral load in plasma-derived medicinal products. Added to this, strengthening of the surveillance and monitoring of ZIKV as well as avoiding travel to Zika infected areas would aid in keeping viral infection under check. Here, we discuss the salient advances in the prevention and control strategies to combat ZIKV with a focus on highlighting various intervention approaches against the vector mosquitoes of this viral pathogen along with presenting an overview regarding human intervention measures to counter other modes of ZIKV transmission and spread. Additionally, owing to the success of vaccines for a number of infections globally, a separate section dealing with advances in ZIKV vaccines and transmission blocking vaccines has also been included.

An evolutionary NS1 mutation enhances Zika virus evasion of host interferon induction

Virus-host interactions determine an infection outcome. The Asian lineage of Zika virus (ZIKV), responsible for the recent epidemics, has fixed a mutation in the NS1 gene after 2012 that enhances mosquito infection. Here we report that the same mutation confers NS1 to inhibit interferon-β induction. This mutation enables NS1 binding to TBK1 and reduces TBK1 phosphorylation. Engineering the mutation into a pre-epidemic ZIKV strain debilitates the virus for interferon-β induction; reversing the mutation in an epidemic ZIKV strain invigorates the virus for interferon-β induction; these mutational effects are lost in IRF3-knockout cells. Additionally, ZIKV NS2A, NS2B, NS4A, NS4B, and NS5 can also suppress interferon-β production through targeting distinct components of the RIG-I pathway; however, for these proteins, no antagonistic difference is observed among various ZIKV strains. Our results support the mechanism that ZIKV has accumulated mutation(s) that increases the ability to evade immune response and potentiates infection and epidemics.

Using immunocompromised mice to identify mechanisms of Zika virus transmission and pathogenesis

Zika virus (ZIKV) is responsible for a recent global epidemic that has been associated with congenital brain malformations in fetuses and with Guillain-Barré syndrome in adults. Within the last 2 years, a major effort has been made to develop murine models to study the mechanism of viral transmission, pathogenesis and the host immune response. Here, we discuss the findings from these models regarding the role that the innate and adaptive immune responses have in controlling ZIKV infection and pathogenesis. Additionally, we examine how innate and adaptive immune responses influence sexual and vertical transmission of ZIKV infection as well as how these responses can influence the ability of ZIKV to cross the placenta and to induce damage in the developing brain.

Current concerns and perspectives on Zika virus co-infection with arboviruses and HIV

Dissemination of vector-borne viruses, such as Zika virus (ZIKV), in tropical and sub-tropical regions has a complicated impact on the immunopathogenesis of other endemic viruses such as dengue virus (DENV), chikungunya virus (CHIKV) and human immunodeficiency virus (HIV). The consequences of the possible co-infections with these viruses have specifically shown significant impact on the treatment and vaccination strategies. ZIKV is a mosquito-borne flavivirus from African and Asian lineages that causes neurological complications in infected humans. Many of DENV and CHIKV endemic regions have been experiencing outbreaks of ZIKV infection. Intriguingly, the mosquitoes, Aedes Aegypti and Aedes Albopictus, can simultaneously transmit all the combinations of ZIKV, DENV, and CHIKV to the humans. The co-circulation of these viruses leads to a complicated immune response due to the pre-existence or co-existence of ZIKV infection with DENV and CHIKV infections. The non-vector transmission of ZIKV, especially, via sexual intercourse and placenta represents an additional burden that may hander the treatment strategies of other sexually transmitted diseases such as HIV. Collectively, ZIKV co-circulation and co-infection with other viruses have inevitable impact on the host immune response, diagnosis techniques, and vaccine development strategies for the control of these co-infections.

Small Molecules and Antibodies for Zika Therapy

Zika virus (ZIKV) infection during pregnancy can cause devastating congenital abnormities or fetal demise. Zika virus infection could also cause Guillain-Barré syndrome in adults. Mosquito control, vaccine, and therapeutics are 3 potential, effective means to prevent ZIKV infection. Here we review the current status of ZIKV drug discovery. Both small molecule inhibitors and therapeutic antibodies have been identified, some of which have shown promising efficacy in mouse models. Most inhibitors were identified through screening US Food and Drug Administration-approved drugs and clinical trial compounds; however, none of them were potent enough to justify a ZIKV clinical trial. Such a repurposing approach has also been pursued for dengue therapy, with several compounds tested in clinical trials showing no clinical benefits. Because pregnant women are the main target population for ZIKV treatment, therapeutic candidates could be developed through a 2-stage path. The first stage should demonstrate safety and efficacy in nonpregnant patients. Once efficacy has been demonstrated in nonpregnant patients, the candidates should be rapidly advanced to stage 2 for safety and efficacy evaluation in pregnant patients. The 2-stage developmental path is supported by previous results from trials with other viral infections that showed that treatment of pregnant women with antiviral drugs or hyperimmunoglobulins significantly reduced congenital abnormalities in neonates.

Preconceptual Zika virus asymptomatic infection protects against secondary prenatal infection

Pregnant women, and their fetal offspring, are uniquely susceptible to Zika virus and other microbial pathogens capable of congenital fetal infection. Unavoidable exposure to Zika virus in endemic areas underscores the need for identifying at-risk individuals, and protecting expecting mothers and their fetal offspring against prenatal infection. Here we show that primary Zika virus asymptomatic infection in mice confers protection against re-infection, and that these protective benefits are maintained during pregnancy. Zika virus recovery was sharply reduced in maternal tissues and amongst fetal concepti after prenatal challenge in mothers with resolved subclinical infection prior to pregnancy compared with mice undergoing primary prenatal infection. These benefits coincide with expanded accumulation of viral-specific antibodies in maternal serum and fetal tissues that protect against infection by the identical or heterologous Zika virus genotype strains. Thus, preconceptual infection primes Zika virus-specific antibodies that confer cross-genotype protection against re-infection during pregnancy.