Recent advances in understanding Crimean–Congo hemorrhagic fever virus [version 1; referees: 4 approved]

Crimean-Congo hemorrhagic fever virus (CCHFV) is a widely distributed hemorrhagic fever virus and the cause of hemorrhagic disease in Africa, Southern and Eastern Europe, the Middle East, India and Asia. Recent emergence of CCHFV into Spain indicates that the geographic range of this virus is expanding and the presence of its tick vector in several countries without reported disease suggest that CCHFV will continue to spread. Research into CCHFV was historically limited by a lack of suitable animal models and tools to study viral pathogenesis. However, in the past few years the toolset for studying CCHFV has expanded with small animal and non-human primate models for CCHFV being developed along with a reverse genetics system that allows for investigation of viral determinants of disease. These tools have been utilized to understand how CCHFV antagonizes host restriction factors and to develop novel vaccine candidates that may help limit the substantial morbidity and mortality in humans caused by CCHFV

Mutations in the E2 glycoprotein and the 3\u27 untranslated region enhance chikungunya virus virulence in mice

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes debilitating musculoskeletal pain and inflammation and can persist for months to years after acute infection. Although studies of humans and experimentally infected animals suggest that CHIKV infection persists in musculoskeletal tissues, the mechanisms for this remain poorly understood. To evaluate this further, we isolated CHIKV from the serum of persistently infected Rag1 -/- mice at day 28. When inoculated into naive wild-type (WT) mice, this persistently circulating CHIKV strain displayed a capacity for earlier dissemination and greater pathogenicity than the parental virus. Sequence analysis revealed a nonsynonymous mutation in the E2 glycoprotein (E2 K200R) and a deletion within the 3' untranslated region (3'-UTR). The introduction of these changes into the parental virus conferred enhanced virulence in mice, although primary tropism for musculoskeletal tissues was maintained. The E2 K200R mutation was largely responsible for enhanced viral dissemination and pathogenicity, although these effects were augmented by the 3'- UTR deletion. Finally, studies with Irf3/Irf7 -/- and Ifnar1 -/- mice suggest that the E2 K200R mutation enhances viral dissemination from the site of inoculation independently of interferon regulatory factor 3 (IRF3)-, IRF7-, and IFNAR1-mediated responses. As our findings reveal viral determinants of CHIKV dissemination and pathogenicity, their further study should help to elucidate host-virus interactions that determine acute and chronic CHIKV infection

Animal Models of Chikungunya Virus Infection and Disease

Chikungunya virus (CHIKV) is a reemerging alphavirus that causes acute febrile illness and severe joint pain in humans. Although acute symptoms often resolve within a few days, chronic joint and muscle pain can be long lasting. In the last decade, CHIKV has caused widespread outbreaks of unprecedented scale in the Americas, Asia, and the Indian Ocean island regions. Despite these outbreaks and the continued expansion of CHIKV into new areas, mechanisms of chikungunya pathogenesis and disease are not well understood. Experimental animal models are indispensable to the field of CHIKV research. The most commonly used experimental animal models of CHIKV infection are mice and nonhuman primates; each model has its advantages for studying different aspects of CHIKV disease. This review will provide an overview of animal models used to study CHIKV infection and disease and major advances in our understanding of chikungunya obtained from studies performed in these models

A 44-Nucleotide Region in the Chikungunya Virus 3′ UTR Dictates Viral Fitness in Disparate Host Cells

We previously reported that deletion of a 44-nucleotide element in the 3′ untranslated region (UTR) of the Chikungunya virus (CHIKV) genome enhances the virulence of CHIKV infection in mice. Here, we find that while this 44-nucleotide deletion enhances CHIKV fitness in murine embryonic fibroblasts in a manner independent of the type I interferon response, the same mutation decreases viral fitness in C6/36 mosquito cells. Further, the fitness advantage conferred by the UTR deletion in mammalian cells is maintained in vivo in a mouse model of CHIKV dissemination. Finally, SHAPE-MaP analysis of the CHIKV 3′ UTR revealed this 44-nucleotide element forms a distinctive two-stem-loop structure that is ablated in the mutant 3′ UTR without altering additional 3′ UTR RNA secondary structures

T-Cells and Interferon Gamma Are Necessary for Survival Following Crimean-Congo Hemorrhagic Fever Virus Infection in Mice

Crimean-Congo hemorrhagic fever (CCHF) is a severe tick-borne febrile illness with wide geographic distribution. In humans, the disease follows infection by the Crimean-Congo hemorrhagic fever virus (CCHFV) and begins as flu-like symptoms that can rapidly progress to hemorrhaging and death. Case fatality rates can be as high as 30%. An important gap in our understanding of CCHF are the host immune responses necessary to control the infection. A better understanding of these responses is needed to direct therapeutic strategies to limit the often-severe morbidity and mortality seen in humans. In this report, we have utilized a mouse model in which mice develop severe disease but ultimately recover. T-cells were robustly activated, differentiated to produce antiviral cytokines, and were critical for survival following CCHFV infection. We further identified a key role for interferon gamma (IFNγ) in survival following CCHFV infection. These results significantly improve our understanding of the host adaptive immune response to severe CCHFV infection

The Role of Adaptive Mutations in Mouse Adapted Crimean-Congo Hemorrhagic Fever Virus

Crimean-Congo Hemorrhagic Fever Virus (CCHFV) is endemic in Europe, Asia, and Africa. The geographic distribution of CCHFV is expanding as Hyalomma ticks, the main carriers of the virus, migrate northward. Infection with CCHFV initially manifests with non-specific symptoms including fever, muscle pains, and nausea that may progress into a hemorrhagic phase characterized by severe bleeding throughout the body. The case fatality rate is reported to range between 9-50%. With increasing numbers of humans at risk, further understanding of how the virus causes disease is essential for developing effective therapeutics. Studies investigating the host and viral determinants of pathogenesis, however, have been constrained due to mouse models requiring mice to be deficient in initial innate immune responses to manifest CCHFV disease symptoms after infection. However, we have recently developed a mouse-adapted CCHFV (MA-CCHFV) which presents with disease similar to human CCHFV cases in fully immunocompetent mice. We hypothesize that adaptive mutations in MA-CCHFV have enabled the virus to overcome mouse innate immunity and cause disease in immunocompetent mice. CCHFV is an RNA virus with three genomic segments. The S segment encodes the nucleoprotein (NP) and a non-structural protein (NSs) while the M segment encodes a large multi-unit protein which is later cleaved into two structural glycoproteins and three non-structural proteins. The L segment has largely unknown function(s) but does encode a protein required for viral replication. Compared to parental strain CCHFV-Hoti, MA-CCHFV has 6 mutations which result in changes to proteins encoded by the virus. Two mutations occur in the NP, one in the NSs, two in the M segment non-structural proteins GP38 and NSm and two in the viral L protein. These mutations likely indicate key proteins CCHFV uses as virulence factors to cause severe disease. To determine the role of these adaptations, we are examining the responses of human and mouse cell lines to infection with parental and MA-CCHFV strains. In addition, we can express the viral proteins independently of the virus to isolate the specific roles of these proteins and understand how they affect the initial immune responses in mouse cells. Understanding how these mutated proteins uniquely interact with the mouse immune system will help identify the host and viral determinants of CCHFV-induced disease. This will support new avenues of focus in CCHFV research to develop effective therapeutics and vaccines. This research is funded by the Intramural Research Program, NIAID, NIH

A Look into <i>Bunyavirales</i> Genomes: Functions of Non-Structural (NS) Proteins

In 2016, the Bunyavirales order was established by the International Committee on Taxonomy of Viruses (ICTV) to incorporate the increasing number of related viruses across 13 viral families. While diverse, four of the families (Peribunyaviridae, Nairoviridae, Hantaviridae, and Phenuiviridae) contain known human pathogens and share a similar tri-segmented, negative-sense RNA genomic organization. In addition to the nucleoprotein and envelope glycoproteins encoded by the small and medium segments, respectively, many of the viruses in these families also encode for non-structural (NS) NSs and NSm proteins. The NSs of Phenuiviridae is the most extensively studied as a host interferon antagonist, functioning through a variety of mechanisms seen throughout the other three families. In addition, functions impacting cellular apoptosis, chromatin organization, and transcriptional activities, to name a few, are possessed by NSs across the families. Peribunyaviridae, Nairoviridae, and Phenuiviridae also encode an NSm, although less extensively studied than NSs, that has roles in antagonizing immune responses, promoting viral assembly and infectivity, and even maintenance of infection in host mosquito vectors. Overall, the similar and divergent roles of NS proteins of these human pathogenic Bunyavirales are of particular interest in understanding disease progression, viral pathogenesis, and developing strategies for interventions and treatments

An Intramuscular DNA Vaccine for SARS-CoV-2 Decreases Viral Lung Load but Not Lung Pathology in Syrian Hamsters

The 2019 novel coronavirus, SARS-CoV-2, first reported in December 2019, has infected over 102 million people around the world as of February 2021 and thus calls for rapid development of safe and effective interventions, namely vaccines. In our study, we evaluated a DNA vaccine against SARS-CoV-2 in the Syrian hamster model. Hamsters were vaccinated with a DNA-plasmid encoding the SARS-CoV-2 full length spike open reading frame (ORF) to induce host cells to produce spike protein and protective immune responses before exposure to infectious virus. We tested this vaccine candidate by both intranasal (IN) and intramuscular (IM) routes of administration and complexing with and without an in vivo delivery reagent. Hamsters receiving prime-boost-boost IM-only vaccinations recovered body weight quicker, had decreased lung viral loads, and increased SARS-CoV-2-specific antibody titers compared to control vaccinated animals but, surprisingly, lung pathology was as severe as sham vaccinated controls. The IM/IN combination group showed no efficacy in reducing lung virus titers or pathology. With increasing public health need for rapid and effective interventions, our data demonstrate that in some vaccine contexts, significant antibody responses and decreased viral loads may not be sufficient to prevent lung pathology

An RNA Vaccine Protects against Crimean-Congo Hemorrhagic Fever Virus Infection in Mice

Crimean-Congo Hemorrhagic Fever Virus (CCHFV) is commonly transmitted by ticks and has a wide geographic distribution, being endemic throughout southern and eastern Europe, the Middle East, Asia, and Africa. Due to climate change, this range is even expanding northward. CCHFV causes a hemorrhagic disease characterized by initial non-specific illness (fever, muscle pains, nausea) followed by severe internal and external bleeding with a case fatality rate of 5-60%. As there is no licensed therapeutics or vaccines, there is great need for highly effective countermeasures. Recently, we have developed a self-replicating RNA-based vaccine which expresses two of the viral proteins: the CCHFV nucleoprotein (repNP) and glycoprotein precursor (repGPC) and is highly protective against a lethal viral challenge in mice. We found that vaccination with this vaccine prevented disease and conferred 100% survival against a lethal CCHFV infection in mice. This vaccine significantly stimulated both antibody-producing B-cells and T-cells which kill infected cells. Our repNP vaccination primarily stimulated B-cells to produce anti-NP antibodies while repGPC primarily stimulated the T-cells. To confirm whether B-cells or T-cells are most responsible for protection, we vaccinated mice lacking B- or T-cells. While mice lacking T-cells survived, B-cell deficient mice only had ~40% survival indicating that the B-cells and antibodies are essential to confer protection. Currently, this vaccine is undergoing further preclinical testing in preparation for human clinical trials while ongoing studies are continuing to investigate how these antibodies protect against CCHFV so that we may improve additional and much needed CCHFV therapeutics. This research was funded by the Intramural Research Program, NIAID, NIH

Species-specific MARCO-alphavirus interactions dictate chikungunya virus viremia

Summary: Arboviruses are public health threats that cause explosive outbreaks. Major determinants of arbovirus transmission, geographic spread, and pathogenesis are the magnitude and duration of viremia in vertebrate hosts. Previously, we determined that multiple alphaviruses are cleared efficiently from murine circulation by the scavenger receptor MARCO (Macrophage receptor with collagenous structure). Here, we define biochemical features on chikungunya (CHIKV), o’nyong ’nyong (ONNV), and Ross River (RRV) viruses required for MARCO-dependent clearance in vivo. In vitro, MARCO expression promotes binding and internalization of CHIKV, ONNV, and RRV via the scavenger receptor cysteine-rich (SRCR) domain. Furthermore, we observe species-specific effects of the MARCO SRCR domain on CHIKV internalization, where those from known amplification hosts fail to promote CHIKV internalization. Consistent with this observation, CHIKV is inefficiently cleared from the circulation of rhesus macaques in contrast with mice. These findings suggest a role for MARCO in determining whether a vertebrate serves as an amplification or dead-end host following CHIKV infection