Pregnancy represents a uniquely vulnerable period during which viral infections can exert profound effects on maternal health, placental function, and fetal development. Over the past 30 years, emerging and re-emerging viruses, including flaviviruses, coronaviruses, poxviruses, orthomyxoviruses, paramyxoviruses, and filoviruses, have repeatedly demonstrated their capacity to disrupt pregnancy through diverse mechanisms that extend far beyond classical teratogenic outcomes. Nearly every major viral outbreak has revealed a critical gap in our understanding of maternal susceptibility during pregnancy. In this review, we will examine how emerging and re-emerging viruses threaten pregnancy across multiple biological scales, ranging from congenital infection, placental dysfunction, maternal immune dysregulation, and infertility, focusing on modern day viruses from a range of families. Understanding the mechanisms by which reproductive health can be impacted by these viruses and integrating this knowledge in developing care, prevention, and intervention strategies tailored to pregnancy and reproduction should be a foundational part of global health and preparedness.
Human endogenous retroviruses (HERVs) provide a direct record of the millions of years of co-evolution between humans and viruses. Yet, due to their repetitive nature and former reputation as "junk DNA," a full characterization of the functional roles and transcriptional regulation of HERVs remains to be achieved. As sequencing technologies improve, better resolution data regarding HERV expression and regulation has become attainable, and there is mounting evidence of aberrant HERV expression in various human diseases, particularly cancer. However, the perturbations to the transcriptional regulatory processes that govern these endogenized retroviral elements in cancer remain unclear. In this review, we will summarize the state of our understanding of the various mechanisms that control HERV expression in cancer, focusing primarily on aberrant methylation and KRAB-domain containing zinc finger proteins (KZFPs), among others. Many of these regulatory mechanisms are employed in stem cells to regulate pluripotency and differentiation and are also deployed in a subpopulation of cancer cells with high self-renewal and proliferation capacity, called cancer stem cells. While the expression of specific HERVs in cancer could be beneficial, deleterious, or neutral, the potential to use HERVs as biomarkers or immune adjuvants to enhance immunotherapies against cancer is promising. The implications of shared transcriptional mechanisms across cancer and stem cells will expose new areas to intervene with cancer treatments, ushering in a new era of HERV-based cancer therapeutics and diagnostics.
The vertical transmission of tomato viruses through seeds and pollen is a significant yet often overlooked pathway for the persistence and global spread of these pathogens. This review provides a comprehensive synthesis of current knowledge on the mechanisms, epidemiological implications, and management strategies of vertically transmitted tomato viruses. While recent advances in diagnostic techniques such as high-throughput sequencing (HTS), have improved virus detection, key research gaps remain in understanding the molecular and ecological dynamics of seed and pollen transmission. The interaction between vertical and horizontal transmission modes complicates virus epidemiology, necessitating an integrated management approach that includes rigorous seed health testing, genetic resistance breeding, and biosecurity measures. Emerging threats, such as resistance-breaking virus strains and the impact of climate change on vector distribution, underscore the need for enhanced surveillance and stronger international regulatory cooperation. This review highlights the need for interdisciplinary research and collaboration to develop sustainable virus mitigation strategies. Future research priorities include optimizing detection methods, exploring next-generation breeding technologies, and strengthening international biosecurity frameworks to safeguard global tomato production against the growing threat of vertically transmitted viruses.
Plant virus emergence is a major threat for agricultural production and for the preservation of biodiversity in wild ecosystems. This process is determined by genetic and ecological factors and, among the latter, one of the most important is the chance for the virus to encounter susceptible plant populations. Seed transmission has a great potential to facilitate such encounters: from allowing plant viruses to persist locally over unfavorable conditions such as the absence of susceptible hosts, to mediate long range dissemination to reach distant plant populations that could not otherwise be invaded. Here, we review current knowledge on the relationship between plant virus seed transmission and emergence, and on its consequences for the epidemiology of these pathogens. We start by setting up a conceptual framework based on mathematical modelling. Then, we summarize experimental and empirical evidence supporting the central role of seed transmission for initiating damaging plant virus-induced disease epidemics, at different geographical scales and in wild and cultivated plant populations. Finaly, we explore current methodologies to limit the emergence of plant viruses associated with seed transmission. Considering these studies, we propose avenues for future research on this subject.
RNA interference (RNAi) is emerging as a powerful technology to potentially protect wheat and barley crops from plant viruses such as Luteovirus pashordei, historicaly known as barley yellow dwarf virus (BYDV), and insect/vector pest infestation. The induction of the RNAi mechanism by the spray on delivery of double-stranded (ds) RNAs that display homology to vital genes encoding virus movement protein, coat protein and other genes related to the virus-plant or virus-vector interaction can lead to limiting virus infection and replication as well as its transmission by aphid vectors. Introducing small interfering RNA (siRNA) into plant cells, targeting these genes, is initiated using various delivery methods, where the most promising is termed spray induced gene silencing (SIGS). This review overviews the significance of barley yellow dwarf viruses (BYDVs) and their aphid vectors. We examine RNAi technology with a focus on the potential for SIGS as a sustainable and environmentally friendly solution for combating barley yellows disease (BYD) in grain crops. The discussion also covers the applications approaches, advantages and disadvantages of this technology, its in-field implementation, the challenges SIGS RNAi application faces and potential for future directions.
Domestic pigs are a vital component of the global food supply, with a population nearing 780 million worldwide, making them one of the most commonly raised livestock. As pig production intensifies, the associated practices and environmental conditions may elevate the risk of emergence and spread of zoonotic agents, including ebolaviruses. Previously, we demonstrated that experimentall infection with Orthoebolavirus bundibugyoense and Orthoebolavirus restonense in pigs caused sub-clinical signs, with only a few animals exhibiting elevated temperatures and limited signs of acute respiratory distress. In this study, we sought to describe immune-related gene exression changes following those viral infections in pigs. Our findings revealed no significant changes in infection- and inflammation-related cytokines, but a strong adaptive immune response was observed in the lungs and tracheobronchial lymph nodes. Comparative analysis with a study in which non-human primates were experimentally infected with Orthoebolavirus bundibugyoense, where the virus is lethal, revealed molecular similarities in gene expression. This may suggest that certain viral processes may be conserved across species. These results highlight the potential role of pigs in ebolavirus spillover dynamics and underscore the importance of understanding the role of livestock in the emergence of these pathogens to guide prevention and mitigation strategies.
Human maximum containment facilities-also known as biosafety level 4 (BSL-4) laboratories-for zoonotic viruses such as Ebola virus or Nipah virus and veterinary maximum containment (BSL-4vet) facilities, e.g. for foot-and-mouth disease virus or peste-de-petits-ruminants virus, share many similar features but also differ in their design, standard operating procedures and operational requirements. This article summarizes the similarities and differences by addressing relevant aspects of these two types of maximum containment facilities. Construction and operation of both facilities is bound by strict regulations and regular audits by national or state authorities. The technical infrastructure is similar with respect to air handling, negative pressure differential to the outside and between rooms, as well as autoclaves and waste water handling. Both facilities require strict access control and training for entry into the area, which is more extensive on the human maximum containment side. Special personal protective equipment such as a positive pressure suits needs to be worn in the human maximum containment facility, but this is not generally necessary in veterinary facilities. Exiting the facility requires showering of personnel-a personal shower only in the veterinary containment and at least a chemical shower to decontaminate the suit in the human containment. Removal of samples from both kinds of facilities can only occur after application of strict and validated inactivation protocols. In addition, both facilities undergo room decontamination processes for maintenance or between animal studies. Overall, we would like to demonstrate that these facilities have more in common than expected at first glance and close coordination and cooperation between the individuals responsible for them is advisable.
Sudan virus (SUDV) causes highly lethal outbreaks of hemorrhagic disease throughout Africa, but there has yet to be an approved vaccine or therapeutic to combat this public health threat. The most common route of natural exposure to filoviruses is through mucosal contact which greatly impacts initial viral replication. Historically, SUDV animal models used an intramuscular infection route. Here, we sought to further characterize an animal model using mucosal challenge routes and compared the impact that intramuscular, intranasal, or aerosol exposure had on SUDV pathogenicity in a ferret model. We determined that the route of infection did not significantly impact overall SUDV pathogenicity; only subtle changes were detected in magnitude of viremia and oral viral shedding. Additionally, we sought to determine if preexisting Lloviu virus (LLOV) immunity could protect ferrets from lethal SUDV infection. We found that the previous immunity elicited by LLOV infection was not sufficient to protect ferrets from lethal SUDV disease. In conclusion, our results indicate that the infection route has minimal effect on overall pathogenicity of SUDV in ferrets and that prior LLOV infection does not elicit a cross-protective immune response to SUDV.
Concern over spillover events caused by high-consequence pathogens has grown in recent years due to the increased occurrence of such events, and because the COVID-19 pandemic demonstrated how severe the consequences of spillover events can be. As such, there is escalading interest in uncovering the factors that make spillover events more likely, specifically for high-consequence pathogens. An important aspect of this work involves researching how high-consequence pathogens interact with their reservoir hosts. Thus, this chapter discusses the importance of studying high-consequence pathogens in their reservoir hosts, specifically in experimental laboratory settings, with a special emphasis on Sin Nombre virus and Lassa virus, and their respective rodent reservoir hosts, Peromyscus maniculatus and Mastomys natalensis. Value gained from this research, as well as the current limitations faced when conducting this work are also discussed. Overall, this work helps to shed light on various aspects of these pathogens such as their transmission patterns, pathogenesis (and lack thereof), and mechanisms of persistence in their reservoir hosts. Limitations include a need for highly developed laboratory infrastructure, demanding funding requirements, and a lack of compatible reagents for the exotic species that are often the subject of these studies. Continued interest and research is needed to expand this work to include host reservoirs of other high consequence pathogens so that the risks of future spillover events can be mitigated as best as possible.
Bats are the reservoir hosts for a diverse range of viruses, including some that are highly pathogenic to humans, yet they generally harbor these pathogens without showing symptoms. This unique tolerance to viral infection makes them a critical model to study virus-host interactions and immune responses. Immunological in vivo studies in bats are however often hampered by low reproducibility, a lack of specific reagents, limited access to adequate facilities and availability of inbred bat colonies to perform experiments. In order to overcome these challenges, we have developed a bat xenograft mouse model by intravenously engrafting mice with Rousettus aegyptiacus bone marrow (bat immune system mice; BIS-mice). R. aegyptiacus is of special interest since it is the reservoir host of Marburg virus (MARV). Here we show that MARV does not cause morbidity in bat-engrafted mice, while Ebola virus (EBOV) seems to be highly lethal in this model. Further transcriptome analysis of MARV and EBOV infected BIS-mice revealed that the infection route significantly influences gene expression profiles in host tissues. Additionally, distinct gene expression patterns were observed in BIS-mice when comparing EBOV and MARV infection, underscoring virus-specific timing and intensity of immune gene activation, with MARV typically inducing earlier and more sustained antiviral responses compared to EBOV, which triggers a pronounced inflammatory response. This study demonstrates, for the first time, the use of BIS-mice to study filovirus immunopathogenesis. Additionally, it establishes a crucial foundation for generating bat species-specific immune mouse models, enabling in-depth characterization of bat-borne viruses and promoting translational research in this field.
In the present study, effective inactivation protocols were successfully developed and validated for the two airborne room disinfection methods vaporized hydrogen peroxide (VHP, H2O2) and dry fogging of aerosolized peroxyacetic acid (aPAA). Both methods were tested within the same HEPA filter housing (HEPA FH), allowing a direct comparison in an identical experimental setup. This approach provided a detailed comparison of their respective advantages and disadvantages. The main focus was on the determination of the microbicidal efficacy. This is the first time, that the efficacy of both methods has been clearly demonstrated for the most relevant classes of microorganisms using a broad spectrum of different test organisms. During the development phase of the respective optimal inactivation protocols the efficacy of the aPAA process was shown to correspond to the generally accepted microbicidal efficacy profile, whereas the efficacy pattern of the VHP process differed significantly from this. The VHP method demonstrated an exceptionally high sporicidal efficacy, significantly exceeding the measurable antiviral efficacy against both non-enveloped and even enveloped viruses. Moreover, even by reducing the used hydrogen peroxide (HP) amount drastically, no protocol could be applied in which the mycobacterial and the bacterial spore carriers were not be sufficiently inactivated. Based on these clear results, the current practice of using almost exclusively bacterial spore carriers for the establishment and validation of VHP-based inactivation protocols in particular have to be adjusted. Safe and effective inactivation protocols can only be developed by using suitable test organisms adapted to the respective individual requirements.
The Filoviridae family encompasses Ebola virus (EBOV) and Marburg virus (MARV), some of the most lethal viruses known to cause sporadic, recurring outbreaks of severe hemorrhagic fever mainly throughout central Africa. However, other lesser-known viruses also belong to the filovirus family as they are closely related, such as Bundibugyo, Reston and Taï Forest virus. These viruses differ in their virulence in humans significantly: while EBOV and MARV show lethality in humans of up to 90 %, Reston virus appears to be avirulent in humans. Here, underlying molecular factors leading to differences in virulence via changes in filovirus entry, replication and immune evasion strategies are summarized and assessed. While the filovirus glycoprotein contributes towards virulence by facilitating entry into a wide variety of tissues, differences in virus-host interactions and replication efficacies lead to measurable variances of progeny virus production. Additionally, immune evasion strategies lead to alterations in replication efficacy thus changing who has the upper hand between the virus and the host. Understanding and unraveling the contributions of these molecular determinants on filovirus virulence provide insights into the processes causing the underlying pathogenesis. It will further help to assess the pathogenicity of newly discovered filoviruses. Finally, these molecular determinants and processes present attractive targets for therapeutic intervention and development of novel antiviral countermeasures.
Zoonotic paramyxoviruses, including the highly pathogenic henipaviruses (HNVs), pose significant risks to global health due to their high mortality rates, potential for human-to-human transmission, and lack of approved countermeasures. Recent metagenomic surveys have uncovered an extensive diversity of HNVs and related paramyxoviruses circulating in wildlife, the majority of which remain uncharacterized due to the dearth of viral isolates. In lieu of viral isolates, reverse genetics systems offer an approach to derive infectious clones de novo in the laboratory, facilitating research into the biology, zoonotic potential, and pathogenicity of novel HNVs. This chapter explores the methodologies and applications of reverse genetics systems for novel HNVs, including considerations for virus sequence validation, full-length virus recovery, and the development of platforms such as minigenomes, replicons, and virus replicon particles. Such biologically-contained life cycle modeling systems enable research to be conducted at lower biocontainment, and provide accessible tools through which to investigate HNV biology. This work demonstrates the versatility of reverse genetics systems in advancing our understanding of high-consequence pathogens, enabling the proactive development of vaccines, antivirals, and diagnostic tools. By integrating these methodologies within a framework of biosafety and biosecurity, researchers can better prepare for and respond to future zoonotic threats.
In response to outbreaks of (re)emerging highly pathogenic RNA viruses, simple and scalable antiviral screening methods are urgently needed. Using established and validated diagnostic methods like RT-PCR for antiviral screening offers a rapid readout of viral replication. This becomes particular important when other traditional viral replication readouts, such as TCID50 or plaque assays cannot be used due to the absence of cytopathic effects, lack of reporter gene-containing recombinant viruses or unavailability of appropriate antibodies - the latter two common challenges when so far unknown viruses emerge. This study evaluated semi-automated diagnostic RT-PCR in a 96-well approach for antiviral compound screening using Marburg virus serving as a case study. Remdesivir, a prodrug that exhibits antiviral activities against multiple RNA viruses, was used as positive control inhibiting replication of filoviruses. Applicability of the protocol to other members of the filovirus family was feasible using the same settings, while for other viruses like Middle East respiratory syndrome coronavirus (MERS-CoV) or Crimean-Congo hemorrhagic fever virus (CCHFV) adaptations to optimal infection settings were necessary. Our results demonstrate a high reproducibility and highlight the rapid adaptability of semi-automated RT-PCR assays as an accelerated antiviral screening assay with high scalability against a wide range of newly or (re)emerging RNA viruses. This is critical especially during outbreak situations where timely antiviral assessments are urgently needed.
Usutu virus (USUV, Flaviviridae) is an emerging arbovirus that has led to epizootic outbreaks in birds and numerous human neuroinvasive disease cases in Europe. It is maintained in an enzootic cycle with Culex mosquitoes and passerine birds, a transmission cycle that is shared by West Nile virus (WNV) and St. Louis encephalitis virus (SLEV), two flaviviruses that are endemic in the United States. USUV and WNV co-circulate in Africa and Europe, and SLEV and WNV co-circulate in North America. These three viruses are prime examples of One Health issues, in which the interactions between humans, animals, and the environments they reside in can have important health impacts. The three facets of One Health are interwoven throughout this article as we discuss the mechanisms of flavivirus transmission and emergence. We explore the possibility of USUV emergence in the United States by analyzing the shared characteristics among USUV, WNV, and SLEV, including the role that flavivirus co-infections and sequential exposures may play in viral emergence. Finally, we provide insights on the importance of integrated surveillance programs as One Health tools that can be used to mitigate USUV emergence and spread.
Schmallenberg virus, an arbovirus of the Orthobunyavirus genus that primarily infects ruminants, emerged in 2011 near the Dutch-German border region and subsequently caused a large number of abortions and the births of severely malformed newborns in the European livestock population. Immediate intensive research led to the development of reliable diagnostic tests, the identification of competent Culicoides vector species, and the elucidation of the pathogenesis in infected vertebrate hosts. In addition, the structure of the major antigenic domain has been elucidated in great detail, leading to the development of effective marker vaccine candidates. The knowledge gained over the last decade on the biology and pathogenesis of SBV and the experience acquired in its control will be of great value in the future for the control of any similar emerging pathogen of veterinary or public health importance such as Shuni or Oropouche virus. However, some important knowledge gaps remain, for example, the factors contributing to the highly variable transmission rate from dam to fetus or the viral factors responsible for the vector competence of Culicoides midges are largely unknown. Thus, questions still remain for the next decade of research on SBV and related viruses.
Norovirus infections are a leading cause of gastroenteritis worldwide. Despite the substantial global health burden and economic impact, there are currently no approved antiviral therapeutics or vaccines. Additionally, much of our knowledge of norovirus comes from experiments using surrogate viruses, such as murine norovirus and feline calicivirus. The challenge surrounding human norovirus research arises from a lack of robust cell culture systems and efficient animal models. In this review, we explore recent advances in the in vitro cultivation of human norovirus and reverse genetics systems and discuss commonly used in vivo models. We summarize the current understanding of both innate and adaptive immune responses to norovirus infection and provide an overview of vaccine strategies and the current clinical trial landscape, with a focus on the only vaccine candidate that has reached phase III clinical development stage.
Resistance to infection by plant viruses involves proteins encoded by plant resistance (R) genes, viz., nucleotide-binding leucine-rich repeats (NLRs), immune receptors. These sensor NLRs are activated either directly or indirectly by viral protein effectors, in effector-triggered immunity, leading to induction of defense signaling pathways, resulting in the synthesis of numerous downstream plant effector molecules that inhibit different stages of the infection cycle, as well as the induction of cell death responses mediated by helper NLRs. Early events in this process involve recognition of the activation of the R gene response by various chaperones and the transport of these complexes to the sites of subsequent events. These events include activation of several kinase cascade pathways, and the syntheses of two master transcriptional regulators, EDS1 and NPR1, as well as the phytohormones salicylic acid, jasmonic acid, and ethylene. The phytohormones, which transit from a primed, resting states to active states, regulate the remainder of the defense signaling pathways, both directly and by crosstalk with each other. This regulation results in the turnover of various suppressors of downstream events and the synthesis of various transcription factors that cooperate and/or compete to induce or suppress transcription of either other regulatory proteins, or plant effector molecules. This network of interactions results in the production of defense effectors acting alone or together with cell death in the infected region, with or without the further activation of non-specific, long-distance resistance. Here, we review the current state of knowledge regarding these processes and the components of the local responses, their interactions, regulation, and crosstalk.
RNA viruses are some of the most successful biological entities due their ability to adapt and evolve. Despite their small genome and parasitic nature, RNA viruses have evolved many mechanisms to ensure their survival and maintenance in the host population. We propose that one of these mechanisms of survival is the generation of nonstandard viral genomes (nsVGs) that accumulate during viral replication. NsVGs are often considered to be accidental defective byproducts of the RNA virus replication, but their ubiquity and the plethora of roles they have during infection indicate that they are an integral part of the virus life cycle. Here we review the different types of nsVGs and discuss how their multiple roles during infection could be beneficial for RNA viruses to be maintained in nature. By shifting our perspectives on what makes a virus successful, we posit that nsVG generation is a conserved phenomenon that arose during RNA virus evolution as an essential component of a healthy virus community.
