Presence of broadly reactive and group-specific neutralizing epitopes on newly described isolates of Crimean-Congo hemorrhagic fever virus

Neutralizing monoclonal antibodies against the Gc fusion loop region of Crimean-Congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever virus (CCHFV) is a highly pathogenic tick-borne virus, prevalent in more than 30 countries worldwide. Human infection by this virus leads to severe illness, with an average case fatality of 40%. There is currently no approved vaccine or drug to treat the disease. Neutralizing antibodies are a promising approach to treat virus infectious diseases. This study generated 37 mouse-derived specific monoclonal antibodies against CCHFV Gc subunit. Neutralization assays using pseudotyped virus and authentic CCHFV identified Gc8, Gc13, and Gc35 as neutralizing antibodies. Among them, Gc13 had the highest neutralizing activity and binding affinity with CCHFV Gc. Consistently, Gc13, but not Gc8 or Gc35, showed in vivo protective efficacy (62.5% survival rate) against CCHFV infection in a lethal mouse infection model. Further characterization studies suggested that Gc8 and Gc13 may recognize a similar, linear epitope in domain II of CCHFV Gc, while Gc35 may recognize a different epitope in Gc. Cryo-electron microscopy of Gc-Fab complexes indicated that both Gc8 and Gc13 bind to the conserved fusion loop region and Gc13 had stronger interactions with sGc-trimers. This was supported by the ability of Gc13 to block CCHFV GP-mediated membrane fusion. Overall, this study provides new therapeutic strategies to treat CCHF and new insights into the interaction between antibodies with CCHFV Gc proteins.

Identification of T cell responses to the nonstructural glycoproteins in survivors of Crimean-Congo hemorrhagic fever in South Africa

Crimean-Congo hemorrhagic fever orthonairovirus (CCHFV) is listed as a priority pathogen by the World Health Organization due to the severity of disease, propensity for spread to nonendemic regions, and absence of a vaccine or specific treatment. The immune correlates of protection are not clearly defined and hence the importance of investigating host immune responses in survivors. We have previously shown that survivors generate memory T cell responses that are long-lived and this study aimed to further define specific viral proteins targeted by the T cell response. The NSM , GP38, highly variable mucin-like domain, and N-terminus of GC regions in CCHFV are considered immunogenic regions and were investigated using peptide libraries representing regions of interest. An interferon gamma ELISpot assay was used to identify responses in peripheral blood mononuclear cells isolated from 12 survivors of laboratory confirmed CCHFV infections. IFN-γ responses were detected from eight survivors, against nine peptides, including four peptides located in the NSM region and five peptides located in the GP38 protein. No response was detected against peptides representing the mucin-like domain. In conclusion, the results suggest the presence of a long-lasting T cell memory response upon stimulation with viral epitopes in survivors of infection.

Evaluation of the immunogenicity of a Crimean-Congo hemorrhagic fever virus vaccine candidate in mice developed based on a baculovirus Zera nanoparticle delivery system

Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic disease caused by Crimean-Congo hemorrhagic fever virus (CCHFV), which can cause severe clinical disease and even death in humans. In recent years, the disease has spread to a wider area, posing a major public health threat to China as well as the Middle East, Europe and Africa, and there is no safe and effective vaccine to prevent the disease. Recently, it has been shown that using the Zera fusion to target proteins can enhance immunogenicity and improve the potential for developing viral vaccines. Based on this finding, in this study, two vaccine candidates, Zera-Gn and Zera-Np, were prepared using an insect baculovirus system expressing CCHFV glycoprotein (Gn) and nucleocapsid protein (Np) fused with Zera tags, and evaluated for immunogenicity in BALB/c mice. The obtainedresults showed that both Zera-Gn and Zera-Np recombinant nanoparticles were successfully expressed, and Zera-Gn had good induction of humoral and cellular immunity in mice, and its immunogenicity was significantly higher than that of Zera-Np. The results indicated that Zera-Gn self-assembled nanoparticles prepared by fusing Zera tags with CCHFV spike-in protein Gn have the potential to be a candidate vaccine for CCHF, and this study provides a reference for the development of Zera self-assembled nanoparticle vaccine for CCHF.

Advances and perspectives in the development of vaccines against highly pathogenic bunyaviruses

Increased human activities around the globe and the rapid development of once rural regions have increased the probability of contact between humans and wild animals. A majority of bunyaviruses are of zoonotic origin, and outbreaks may result in the substantial loss of lives, economy contraction, and social instability. Many bunyaviruses require manipulation in the highest levels of biocontainment, such as Biosafety Level 4 (BSL-4) laboratories, and the scarcity of this resource has limited the development speed of vaccines for these pathogens. Meanwhile, new technologies have been created, and used to innovate vaccines, like the mRNA vaccine platform and bioinformatics-based antigen design. Here, we summarize current vaccine developments for three different bunyaviruses requiring work in the highest levels of biocontainment: Crimean-Congo Hemorrhagic Fever Virus (CCHFV), Rift Valley Fever Virus (RVFV), and Hantaan virus (HTNV), and provide perspectives and potential future directions that can be further explored to advance specific vaccines for humans and livestock.

Evaluation of the immunogenicity of vaccine candidates developed using a baculovirus surface display system for Crimean-Congo hemorrhagic fever virus in mice

Crimean-Congo hemorrhagic fever (CCHF), which has a fatality rate of 20–30%, is widely prevalent in several regions in Asia, Europe, and Africa and has spread to a wider range of areas in recent years. At present, there is a lack of safe and effective vaccines for the prevention of CCHF. In this study, we prepared three vaccine candidates, rvAc-Gn, rvAc-Np, and rvAc-Gn-Np, that encoded the CCHF virus (CCHFV) glycoprotein Gn and the nucleocapsid protein (Np) on the surface of baculovirus using an insect baculovirus vector expression system (BVES) and evaluated their immunogenicity in BALB/c mice. The experimental results showed that both CCHFV Gn and Np were expressed by the respective recombinant baculoviruses and anchored to the viral envelope. BALB/c mice were immunized, and all three recombinant baculoviruses showed significant humoral immunity. At the cellular level, the level of immunity in the rvAc-Gn group was significantly higher than that in the rvAc-Np and rvAc-Gn-Np groups, and the rvAc-Gn-Np coexpression group exhibited the lowest level of cellular immunity. In conclusion, the strategy of coexpressing Gn and Np in the baculovirus surface display system did not result in improvements in immunogenicity, whereas the recombinant baculovirus displaying Gn alone could induce significant humoral and cellular immunity in mice, indicating that rvAc-Gn has potential as a CCHF vaccine candidate. This study thus provides new ideas for the development of a CCHF baculovirus vaccine.

GEM-PA-Based Subunit Vaccines of Crimean Congo Hemor-Rhagic Fever Induces Systemic Immune Responses in Mice

The Crimean Congo Hemorrhagic Fever Virus (CCHFV) is a tick-borne bunyavirus of the Narovirus genus, which is the causative agent of Crimean Congo Hemorrhagic Fever (CCHF). CCHF is endemic in Africa, the Middle East, Eastern Europe and Asia, with a high case-fatality rate of up to 50% in humans. Currently, there are no approved vaccines or effective therapies available for CCHF. The GEM-PA is a safe, versatile and effective carrier system, which offers a cost-efficient, high-throughput platform for recovery and purification of subunit proteins for vaccines. In the present study, based on a GEM-PA surface display system, a GEM-PA based vaccine expressing three subunit vaccine candidates (G-GP, including G-eG_N, G-eG_C and G-NAb) of CCHFV was developed, displaying the ectodomains of the structural glycoproteins eG_N, eG_C and NAb, respectively. According to the immunological assays including indirect-ELISA, a micro-neutralization test of pseudo-virus and ELISpot, 5 μg GPBLP₃ combined with Montanide ISA 201VG plus Poly (I:C) adjuvant (A-G-GP-5 μg) elicited GP-specific humoral and cellular immunity in BALB/c mice after three vaccinations via subcutaneous injection (s.c.). The consistent data between IgG subtype and cytokine detection, ELISpot and cytokine detection indicated balanced Th1 and Th2 responses, of which G-eG_N vaccines could elicit a stronger T-cell response post-vaccination, respectively. Moreover, all three vaccine candidates elicited high TNF-α, IL-6, and IL-10 cytokine levels in the supernatant of stimulated splenocytes in vitro. However, the neutralizing antibody (nAb) was only detected in A-G-eG_C and A-G-eG_C vaccination groups with the highest neutralizing titer of 128, suggesting that G-eG_C could elicit a stronger humoral immune response. In conclusion, the GEM-PA surface display system could provide an efficient and convenient purification method for CCHFV subunit antigens, and the G-GP subunit vaccine candidates will be promising against CCHFV infections with excellent immunogenicity.

Immunobiology of Crimean-Congo hemorrhagic fever

Human infection with Crimean-Congo hemorrhagic fever virus (CCHFV), a tick-borne pathogen in the family Nairoviridae, can result in a spectrum of outcomes, ranging from asymptomatic infection through mild clinical signs to severe or fatal disease. Studies of CCHFV immunobiology have investigated the relationship between innate and adaptive immune responses with disease severity, attempting to elucidate factors associated with differential outcomes. In this article, we begin by highlighting unanswered questions, then review current efforts to answer them. We discuss in detail current clinical studies and research in laboratory animals on CCHF, including immune targets of infection and adaptive and innate immune responses. We summarize data about the role of the immune response in natural infections of animals and humans and experimental studies in vitro and in vivo and from evaluating immune-based therapies and vaccines, and present recommendations for future research.

Structural basis of synergistic neutralization of Crimean-Congo hemorrhagic fever virus by human antibodies

Crimean-Congo hemorrhagic fever virus (CCHFV) is the most widespread tick-borne zoonotic virus, with a 30% case fatality rate in humans. Structural information is lacking in regard to the CCHFV membrane fusion glycoprotein Gc—the main target of the host neutralizing antibody response—as well as antibody–mediated neutralization mechanisms. We describe the structure of prefusion Gc bound to the antigen-binding fragments (Fabs) of two neutralizing antibodies that display synergy when combined, as well as the structure of trimeric, postfusion Gc. The structures show the two Fabs acting in concert to block membrane fusion, with one targeting the fusion loops and the other blocking Gc trimer formation. The structures also revealed the neutralization mechanism of previously reported antibodies against CCHFV, providing the molecular underpinnings essential for developing CCHFV–specific medical countermeasures for epidemic preparedness.

Immunoinformatics guided modeling of CCHF_GN728, an mRNA-based universal vaccine against Crimean-Congo hemorrhagic fever virus

The Crimean-Congo hemorrhagic fever virus (CCHFV) is a lethal human pathogen belonging to the Nairoviridae family that causes Crimean-Congo hemorrhagic fever (CCHF), a tick-borne infection with an alarming mortality rate of up to 80%. CCHFV is the most widespread tick-borne virus with the potential to trigger a pandemic. To date, no vaccines or therapeutics for CCHF have been authorized. In this study, we implemented immunoinformatics approach for developing CCHF_GN728, a universal mRNA-based multi-epitope vaccine against CCHFV. Glycoprotein precursor (GPC) and nucleoprotein (NP) from the virus were selected and screened for potential immunogenic T- and B-cell epitopes. Our developed antigen exhibited the potential to generate 99.95% population coverage worldwide. Stable epitope-allele interaction was confirmed using molecular docking and dynamics simulation. In silico immune simulation corroborated immune cell response to antigen clearance rate. Optimized codons ensured efficient expression of the mRNA in the host cell. The vaccine exhibited stable and strong interactions with the Toll-like receptors. Our findings suggest that the CCHF_GN728 vaccine will trigger specific anti-CCHFV immune responses. Our model is ready for wet-lab experimentation to assess the efficacy of this putative vaccine candidate.

Crimean-Congo Hemorrhagic Fever Virus: Current Advances and Future Prospects of Antiviral Strategies

Crimean-Congo hemorrhagic fever virus (CCHFV) is a widespread, tick-borne pathogen that causes Crimean-Congo hemorrhagic fever (CCHF) with high morbidity and mortality. CCHFV is transmitted to humans through tick bites or direct contact with patients or infected animals with viremia. Currently, climate change and globalization have increased the transmission risk of this biosafety level (BSL)-4 virus. The treatment options of CCHFV infection remain limited and there is no FDA-approved vaccine or specific antivirals, which urges the identification of potential therapeutic targets and the design of CCHF therapies with greater effort. In this article, we discuss the current progress and some future directions in the development of antiviral strategies against CCHFV.

Fine mapping epitope on glycoprotein Gc from Crimean-Congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne zoonosis, caused by CCHF virus (CCHFV) and which there are no diagnostic or therapeutic strategies. The C-terminus of glycoprotein (Gc) encoded by the CCHFV M gene is responsible for CCHFV binding to cellular receptors and acts as a neutralizing-antibody target. In this study, a modified biosynthetic peptide technique (BSP) was used to identify fine epitopes of Gc from the CCHFV YL04057 strain using rabbit antiserum against CCHFV-Gc. Six B cell epitopes (BCEs) and one antigenic peptide (AP) were identified: E1 (⁸⁸VEDASES⁹⁴), E2 (¹¹⁷GDRQVEE¹²³), E3 (²⁴¹EIVTLH²⁴⁶), AP-4 (²⁸¹DFQVYHVGNLLRGDKV²⁹⁶), E5a (³⁷⁰GDTP QLDL³⁷⁷), E5b (³⁷³PQLDLKAR³⁸⁰), and E6 (⁴⁴³HVRSSD⁴⁴⁸). Western blotting analysis showed that each epitope interacted with the positive serum of sheep that had been naturally infected with CCHFV, and the results were consistent with that of Dot-ELISA. The multiple sequence alignment (MSA) revealed high conservation of the identified epitopes among ten CCHFV strains from different areas, except for epitopes AP-4 and E6. Furthermore, three-dimensional structural modeling showed that all identified epitopes were located on the surface of the Gc "head" domain. These mapped epitopes of the CCHFV Gc would provide a basis for further increase our understanding CCHFV glycoprotein function and the development of a CCHFV epitope-based diagnostics vaccine and detection antigen.

Crimean-Congo Hemorrhagic Fever Mouse Model Recapitulating Human Convalescence

Crimean-Congo hemorrhagic fever virus (CCHFV) is a cause of severe hemorrhagic fever. Its tick reservoir and vector are widely distributed throughout Africa, Southern and Eastern Europe, the Middle East, and Asia. Serological evidence suggests that CCHFV can productively infect a wide variety of species, but only humans develop severe, sometimes fatal disease. The role of the host adaptive immunity in control or contribution to the severe pathology seen in CCHF cases is largely unknown. Studies of adaptive immune responses to CCHFV have been limited due to lack of suitable small animal models. Wild-type mice are resistant to CCHFV infection, and type I interferon-deficient mice typically develop a rapid-onset fatal disease prior to development of adaptive immune responses. We report here a mouse model in which type I interferon-deficient mice infected with a clinical isolate of CCHFV develop a severe inflammatory disease but ultimately recover. Recovery was coincident with development of CCHFV-specific B- and T-cell responses that were sustained for weeks postinfection. We also found that recovery from a primary CCHFV infection could protect against disease following homologous or heterologous reinfection. Together this model enables study of multiple aspects of CCHFV pathogenesis, including convalescence, an important aspect of CCHF disease that existing mouse models have been unsuitable for studying.IMPORTANCE The role of antibody or virus-specific T-cell responses in control of acute Crimean-Congo hemorrhagic fever virus infection is largely unclear. This is a critical gap in our understanding of CCHF, and investigation of convalescence following severe acute CCHF has been limited by the lack of suitable small animal models. We report here a mouse model of CCHF in which infected mice develop severe disease but ultimately recover. Although mice developed an inflammatory immune response along with severe liver and spleen pathology, these mice also developed CCHFV-specific B- and T-cell responses and were protected from reinfection. This model provides a valuable tool to investigate how host immune responses control acute CCHFV infection and how these responses may contribute to the severe disease seen in CCHFV-infected humans in order to develop therapeutic interventions that promote protective immune responses.

Animal Models for Crimean-Congo Hemorrhagic Fever Human Disease

Crimean-Congo hemorrhagic fever virus (CCHFV) is an important tick-borne human pathogen endemic throughout Asia, Africa and Europe. CCHFV is also an emerging virus, with recent outbreaks in Western Europe. CCHFV can infect a large number of wild and domesticated mammalian species and some avian species, however the virus does not cause severe disease in these animals, but can produce viremia. In humans, CCHFV infection can lead to a severe, life-threating disease characterized by hemodynamic instability, hepatic injury and neurological disorders, with a worldwide lethality rate of ~20-30%. The pathogenic mechanisms of CCHF are poorly understood, largely due to the dearth of animal models. However, several important animal models have been recently described, including novel murine models and a non-human primate model. In this review, we examine the current knowledge of CCHF-mediated pathogenesis and describe how animal models are helping elucidate the molecular and cellular determinants of disease. This information should serve as a reference for those interested in CCHFV animal models and their utility for evaluation of medical countermeasures (MCMs) and in the study of pathogenesis.

Vesicular Stomatitis Virus-Based Vaccine Protects Mice against Crimean-Congo Hemorrhagic Fever

Crimean-Congo hemorrhagic fever virus (CCHFV), a tick-borne bunyavirus, can cause a life-threatening hemorrhagic syndrome in humans but not in its animal host. The virus is widely distributed throughout southeastern Europe, the Middle East, Africa, and Asia. Disease management has proven difficult and there are no broadly licensed vaccines or therapeutics. Recombinant vesicular stomatitis viruses (rVSV) expressing foreign glycoproteins (GP) have shown promise as experimental vaccines for several viral hemorrhagic fevers. Here, we developed and assessed a replication competent rVSV vector expressing the CCHFV glycoprotein precursor (GPC), which encodes CCHFV structural glycoproteins. This construct drives strong expression of CCHFV-GP, in vitro. Using these vectors, we vaccinated STAT-1 knock-out mice, an animal model for CCHFV. The vector was tolerated and 100% efficacious against challenge from a clinical strain of CCHFV. Anti-CCHFV-GP IgG and neutralizing antibody titers were observed in surviving animals. This study demonstrates that a rVSV expressing only the CCHFV-GP has the potential to serve as a replication competent vaccine platform against CCHF infections.

Diagnostic tests for Crimean-Congo haemorrhagic fever: a widespread tickborne disease

Crimean-Congo haemorrhagic fever (CCHF) is a widespread tickborne disease that circulates in wild and domestic animal hosts, and causes severe and often fatal haemorrhagic fever in infected humans. Due to the lack of treatment options or vaccines, and a high fatality rate, CCHF virus (CCHFV) is considered a high-priority pathogen according to the WHO R&D Blueprint. Several commercial reverse transcriptase PCR (RT-PCR) and serological diagnostic assays for CCHFV are already available, including febrile agent panels to distinguish CCHFV from other viral haemorrhagic fever agents; however, the majority of international laboratories use inhouse assays. As CCHFV has numerous amplifying animal hosts, a cross-sectoral 'One Health' approach to outbreak prevention is recommended to enhance notifications and enable early warning for genetic and epidemiological shifts in the human, animal and tick populations. However, a lack of guidance for surveillance in animals, harmonisation of case identification and validated serodiagnostic kits for animal testing hinders efforts to strengthen surveillance systems. Additionally, as RT-PCR tests tend to be lineage-specific for regional circulating strains, there is a need for pan-lineage sensitive diagnostics. Adaptation of existing tests to point-of-care molecular diagnostic platforms that can be implemented in clinic or field-based settings would be of value given the potential for CCHFV outbreaks in remote or low-resource areas. Finally, improved access to clinical specimens for validation of diagnostics would help to accelerate development of new tests. These gaps should be addressed by updated target product profiles for CCHFV diagnostics.

Exploring Crimean-Congo Hemorrhagic Fever Virus-Induced Hepatic Injury Using Antibody-Mediated Type I Interferon Blockade in Mice

Crimean-Congo hemorrhagic fever virus (CCHFV) can cause severe hepatic injury in humans. However, the mechanism(s) causing this damage is poorly characterized. CCHFV produces an acute disease, including liver damage, in mice lacking type I interferon (IFN-I) signaling due to either STAT-1 gene deletion or disruption of the IFN-I receptor 1 gene. Here, we explored CCHFV-induced liver pathogenesis in mice using an antibody to disrupt IFN-I signaling. When IFN-I blockade was induced within 24 h postexposure to CCHFV, mice developed severe disease with greater than 95% mortality by 6 days postexposure. In addition, we observed increased proinflammatory cytokines, chemoattractants, and liver enzymes in these mice. Extensive liver damage was evident by 4 days postexposure and was characterized by hepatocyte necrosis and the loss of CLEC4F-positive Kupffer cells. Similar experiments in CCHFV-exposed NOD-SCID-γ (NSG), Rag2-deficient, and perforin-deficient mice also demonstrated liver injury, suggesting that cytotoxic immune cells are dispensable for hepatic damage. Some apoptotic liver cells contained viral RNA, while other apoptotic liver cells were negative, suggesting that cell death occurred by both intrinsic and extrinsic mechanisms. Protein and transcriptional analysis of livers revealed that activation of tumor necrosis factor superfamily members occurred by day 4 postexposure, implicating these molecules as factors in liver cell death. These data provide insights into CCHFV-induced hepatic injury and demonstrate the utility of antibody-mediated IFN-I blockade in the study of CCHFV pathogenesis in mice.IMPORTANCE CCHFV is an important human pathogen that is both endemic and emerging throughout Asia, Africa, and Europe. A common feature of acute disease is liver injury ranging from mild to fulminant hepatic failure. The processes through which CCHFV induces severe liver injury are unclear, mostly due to the limitations of existing small-animal systems. The only small-animal model in which CCHFV consistently produces severe liver damage is mice lacking IFN-I signaling. In this study, we used antibody-mediated blockade of IFN-I signaling in mice to study CCHFV liver pathogenesis in various transgenic mouse systems. We found that liver injury did not depend on cytotoxic immune cells and observed extensive activation of death receptor signaling pathways in the liver during acute disease. Furthermore, acute CCHFV infection resulted in a nearly complete loss of Kupffer cells. Our model system provides insight into both the molecular and the cellular features of CCHFV hepatic injury.

Development of vaccines against Crimean-Congo haemorrhagic fever virus

Crimean-Congo haemorrhagic fever virus (CCHFV) is a deadly human pathogen of the utmost seriousness being highly lethal causing devastating disease symptoms that result in intense and prolonged suffering to those infected. During the past 40years, this virus has repeatedly caused sporadic outbreaks responsible for relatively low numbers of human casualties, but with an alarming fatality rate of up to 80% in clinically infected patients. CCHFV is transmitted to humans by Hyalomma ticks and contact with the blood of viremic livestock, additionally cases of human-to-human transmission are not uncommon in nosocomial settings. The incidence of CCHF closely matches the geographical range of permissive ticks, which are widespread throughout Africa, Asia, the Middle East and Europe. As such, CCHFV is the most widespread tick-borne virus on earth. It is a concern that recent data shows the geographic distribution of Hyalomma ticks is expanding. Migratory birds are also disseminating Hyalomma ticks into more northerly parts of Europe thus potentially exposing naïve human populations to CCHFV. The virus has been imported into the UK on two occasions in the last five years with the first fatal case being confirmed in 2012. A licensed vaccine to CCHF is not available. In this review, we discuss the background and complications surrounding this limitation and examine the current status and recent advances in the development of vaccines against CCHFV.

Immunization with DNA Plasmids Coding for Crimean-Congo Hemorrhagic Fever Virus Capsid and Envelope Proteins and/or Virus-Like Particles Induces Protection and Survival in Challenged Mice

Crimean-Congo hemorrhagic fever virus (CCHFV) is a bunyavirus causing severe hemorrhagic fever disease in humans, with high mortality rates. The requirement of a high-containment laboratory and the lack of an animal model hampered the study of the immune response and protection of vaccine candidates. Using the recently developed interferon alpha receptor knockout (IFNAR^−/−) mouse model, which replicates human disease, we investigated the immunogenicity and protection of two novel CCHFV vaccine candidates: a DNA vaccine encoding a ubiquitin-linked version of CCHFV Gc, Gn, and N and one using transcriptionally competent virus-like particles (tc-VLPs). In contrast to most studies that focus on neutralizing antibodies, we measured both humoral and cellular immune responses. We demonstrated a clear and 100% efficient preventive immunity against lethal CCHFV challenge with the DNA vaccine. Interestingly, there was no correlation with the neutralizing antibody titers alone, which were higher in the tc-VLP-vaccinated mice. However, the animals with a lower neutralizing titer, but a dominant cell-mediated Th1 response and a balanced Th2 response, resisted the CCHFV challenge. Moreover, we found that in challenged mice with a Th1 response (immunized by DNA/DNA and boosted by tc-VLPs), the immune response changed to Th2 at day 9 postchallenge. In addition, we were able to identify new linear B-cell epitope regions that are highly conserved between CCHFV strains. Altogether, our results suggest that a predominantly Th1-type immune response provides the most efficient protective immunity against CCHFV challenge. However, we cannot exclude the importance of the neutralizing antibodies as the surviving immunized mice exhibited substantial amounts of them.

IMPORTANCE Crimean-Congo hemorrhagic fever virus (CCHFV) is responsible for hemorrhagic diseases in humans, with a high mortality rate. There is no FDA-approved vaccine, and there are still gaps in our knowledge of the immune responses to infection. The recently developed mouse models mimic human CCHF disease and are useful to study the immunogenicity and the protection by vaccine candidates. Our study shows that mice vaccinated with a specific DNA vaccine were fully protected. Importantly, we show that neutralizing antibodies are not sufficient for protection against CCHFV challenge but that an extra Th1-specific cellular response is required. Moreover, we describe the identification of five conserved B-cell epitopes, of which only one was previously known, that could be of great importance for the development of diagnostics tools and the improvement of vaccine candidates.

Expression and characterization of codon-optimized Crimean-Congo hemorrhagic fever virus Gn glycoprotein in insect cells

Crimean-Congo hemorrhagic fever virus (CCHFV) is a major cause of tick-borne viral hemorrhagic disease in the world. Despite of its importance as a deadly pathogen, there is currently no licensed vaccine against CCHF disease. The attachment glycoprotein of CCHFV (Gn) is a potentially important target for protective antiviral immune responses. To characterize the expression of recombinant CCHFV Gn in an insect-cell-based system, we developed a gene expression system expressing the full-length coding sequence under a polyhedron promoter in Sf9 cells using recombinant baculovirus. Recombinant Gn was purified by affinity chromatography, and the immunoreactivity of the protein was evaluated using sera from patients with confirmed CCHF infection. Codon-optimized Gn was successfully expressed, and the product had the expected molecular weight for CCHFV Gn glycoprotein of 37 kDa. In time course studies, the optimum expression of Gn occurred between 36 and 48 hours postinfection. The immunoreactivity of the recombinant protein in Western blot assay against human sera was positive and was similar to the results obtained with the anti-V5 tag antibody. Additionally, mice were subjected to subcutaneous injection with recombinant Gn, and the cellular and humoral immune response was monitored. The results showed that recombinant Gn protein was highly immunogenic and could elicit high titers of antigen-specific antibodies. Induction of the inflammatory cytokine interferon-gamma and the regulatory cytokine IL-10 was also detected. In conclusion, a recombinant baculovirus harboring CCHFV Gn was constructed and expressed in Sf9 host cells for the first time, and it was demonstrated that this approach is a suitable expression system for producing immunogenic CCHFV Gn protein without any biosafety concerns.

A chronological review of experimental infection studies of the role of wild animals and livestock in the maintenance and transmission of Crimean-Congo hemorrhagic fever virus

This article provides a definitive review of experimental studies of the role of wild animals and livestock in the maintenance and transmission of Crimean-Congo hemorrhagic fever virus (CCHFV), the etiologic agent of Crimean-Congo hemorrhagic fever (CCHF), beginning with the first recognized outbreak of the human disease in Crimea in 1944. Published reports by researchers in the former Soviet Union, Bulgaria, South Africa, and other countries where CCHF has been observed show that CCHFV is maintained in nature in a tick-vertebrate-tick enzootic cycle. Human disease most commonly results from the bite of an infected tick, but may also follow crushing of infected ticks or exposure to the blood and tissues of infected animals during slaughter. Wild and domestic animals are susceptible to infection with CCHFV, but do not develop clinical illness. Vertebrates are important in CCHF epidemiology, as they provide blood meals to support tick populations, transport ticks across wide geographic areas, and transmit CCHFV to ticks and humans during the period of viremia. Many aspects of vertebrate involvement in the maintenance and spread of CCHFV are still poorly understood. Experimental investigations in wild animals and livestock provide important data to aid our understanding of CCHFV ecology. This article is the second in a series of reviews of more than 70 years of research on CCHF, summarizing important findings, identifying gaps in knowledge, and suggesting directions for future research.

Plant-produced candidate countermeasures against emerging and reemerging infections and bioterror agents

Despite progress in the prevention and treatment of infectious diseases, they continue to present a major threat to public health. The frequency of emerging and reemerging infections and the risk of bioterrorism warrant significant efforts towards the development of prophylactic and therapeutic countermeasures. Vaccines are the mainstay of infectious disease prophylaxis. Traditional vaccines, however, are failing to satisfy the global demand because of limited scalability of production systems, long production timelines and product safety concerns. Subunit vaccines are a highly promising alternative to traditional vaccines. Subunit vaccines, as well as monoclonal antibodies and other therapeutic proteins, can be produced in heterologous expression systems based on bacteria, yeast, insect cells or mammalian cells, in shorter times and at higher quantities, and are efficacious and safe. However, current recombinant systems have certain limitations associated with production capacity and cost. Plants are emerging as a promising platform for recombinant protein production due to time and cost efficiency, scalability, lack of harboured mammalian pathogens and possession of the machinery for eukaryotic post-translational protein modification. So far, a variety of subunit vaccines, monoclonal antibodies and therapeutic proteins (antivirals) have been produced in plants as candidate countermeasures against emerging, reemerging and bioterrorism-related infections. Many of these have been extensively evaluated in animal models and some have shown safety and immunogenicity in clinical trials. Here, we overview ongoing efforts to producing such plant-based countermeasures.

Molecular and serological findings in suspected patients with Crimean-Congo hemorrhagic fever virus in Iran

Crimean-Congo hemorrhagic fever (CCHF) is an arthropod-borne disease of humans associated with a severe clinical picture, including hemorrhagic syndrome and a high mortality rate. CCHF virus is widely distributed throughout large areas of the world. To characterize the serological status in CCHF patients, paired clinical samples were collected from suspected CCHF patients and analyzed by microbiological and other laboratory analyses with the aim of: determining the presence of neutralizing antibodies against CCHF virus; investigating the cross-reactivity of these neutralizing antibodies against virus isolated from the same outbreak and against other available laboratory strain; and studying the relationship between the isolated virus with other virus by whole genome sequencing. Patients at Boo-Ali Hospital, Zahedan, Iran, with clinical symptoms ranging from mild to severe hemorrhagic fever were included in the study. Two serum samples were taken from each patient, the first as soon as the patient matched the criteria for CCHF notification and the second when the patient was discharged from hospital (2 weeks later). Commercial and in-house assays revealed a positive IgM signal in acute serum samples from six patients. A novel finding was that CCHF patients develop neutralizing antibodies soon after infection. Interestingly these antibodies were able to neutralize other CCHF virus strains too. The complete sequence of the Zahedan 2007 isolate, including the hitherto unknown first L-segment sequence, was identified using an original clinical sample from one patient with confirmed CCHF infection.

The molecular biology of nairoviruses, an emerging group of tick-borne arboviruses

The nairoviruses are a rapidly emerging group of tick-borne bunyaviruses that includes pathogens of humans (Crimean-Congo hemorrhagic fever virus [CCHFV]) and livestock (Nairobi sheep disease virus [NSDV], also known as Ganjam virus), as well as a large number of viruses for which the normal vertebrate host has not been established. Studies on this group of viruses have been fairly limited, not least because CCHFV is a BSL4 human pathogen, restricting the number of labs able to study the live virus, while NSDV, although highly pathogenic in naive animals, is not seen as a threat in developed countries, making it a low priority. Nevertheless, recent years have seen significant progress in our understanding of the biology of these viruses, particularly that of CCHFV, and this article seeks to draw together our existing knowledge to generate an overall picture of their molecular biology, underlining areas of particular ignorance for future studies.

A novel vaccine against Crimean-Congo Haemorrhagic Fever protects 100% of animals against lethal challenge in a mouse model

Crimean-Congo Haemorrhagic Fever (CCHF) is a severe tick-borne disease, endemic in many countries in Africa, the Middle East, Eastern Europe and Asia. Between 15-70% of reported cases are fatal. There is no approved vaccine available, and preclinical protection in vivo by an experimental vaccine has not been demonstrated previously. In the present study, the attenuated poxvirus vector, Modified Vaccinia virus Ankara, was used to develop a recombinant candidate vaccine expressing the CCHF virus glycoproteins. Cellular and humoral immunogenicity was confirmed in two mouse strains, including type I interferon receptor knockout mice, which are susceptible to CCHF disease. This vaccine protected all recipient animals from lethal disease in a challenge model adapted to represent infection via a tick bite. Histopathology and viral load analysis of protected animals confirmed that they had been exposed to challenge virus, even though they did not exhibit clinical signs. This is the first demonstration of efficacy of a CCHF vaccine.

Possible future monoclonal antibody (mAb)-based therapy against arbovirus infections

More than 150 arboviruses belonging to different families are known to infect humans, causing endemic infections as well as epidemic outbreaks. Effective vaccines to limit the occurrence of some of these infections have been licensed, while for the others several new immunogens are under development mostly for their improvements concerning safety and effectiveness profiles. On the other hand, specific and effective antiviral drugs are not yet available, posing an urgent medical need in particular for emergency cases. Neutralizing monoclonal antibodies (mAbs) have been demonstrated to be effective in the treatment of several infectious diseases as well as in preliminary in vitro and in vivo models of arbovirus-related infections. Given their specific antiviral activity as well-tolerated molecules with limited side effects, mAbs could represent a new therapeutic approach for the development of an effective treatment, as well as useful tools in the study of the host-virus interplay and in the development of more effective immunogens. However, before their use as candidate therapeutics, possible hurdles (e.g., Ab-dependent enhancement of infection, occurrence of viral escape variants) must be carefully evaluated. In this review are described the main arboviruses infecting humans and candidate mAbs to be possibly used in a future passive immunotherapy.

Crimean-Congo hemorrhagic fever: history, epidemiology, pathogenesis, clinical syndrome and genetic diversity

Crimean-Congo hemorrhagic fever (CCHF) is the most important tick-borne viral disease of humans, causing sporadic cases or outbreaks of severe illness across a huge geographic area, from western China to the Middle East and southeastern Europe and throughout most of Africa. CCHFV is maintained in vertical and horizontal transmission cycles involving ixodid ticks and a variety of wild and domestic vertebrates, which do not show signs of illness. The virus circulates in a number of tick genera, but Hyalomma ticks are the principal source of human infection, probably because both immature and adult forms actively seek hosts for the blood meals required at each stage of maturation. CCHF occurs most frequently among agricultural workers following the bite of an infected tick, and to a lesser extent among slaughterhouse workers exposed to the blood and tissues of infected livestock and medical personnel through contact with the body fluids of infected patients. CCHFV is the most genetically diverse of the arboviruses, with nucleotide sequence differences among isolates ranging from 20% for the viral S segment to 31% for the M segment. Viruses with diverse sequences can be found within the same geographic area, while closely related viruses have been isolated in far distant regions, suggesting that widespread dispersion of CCHFV has occurred at times in the past, possibly by ticks carried on migratory birds or through the international livestock trade. Reassortment among genome segments during co-infection of ticks or vertebrates appears to have played an important role in generating diversity, and represents a potential future source of novel viruses. In this article, we first review current knowledge of CCHFV, summarizing its molecular biology, maintenance and transmission, epidemiology and geographic range. We also include an extensive discussion of CCHFV genetic diversity, including maps of the range of the virus with superimposed phylogenetic trees. We then review the features of CCHF, including the clinical syndrome, diagnosis, treatment, pathogenesis, vaccine development and laboratory animal models of CCHF. The paper ends with a discussion of the possible future geographic range of the virus. For the benefit of researchers, we include a Supplementary Table listing all published reports of CCHF cases and outbreaks in the English-language literature, plus some principal articles in other languages, with total case numbers, case fatality rates and all CCHFV strains on GenBank.

Development, screening, and analysis of DNA aptamer libraries potentially useful for diagnosis and passive immunity of arboviruses

BACKGROUND

Nucleic acid aptamers have long demonstrated the capacity to bind viral envelope proteins and to inhibit the progression of pathogenic virus infections. Here we report on initial efforts to develop and screen DNA aptamers against recombinant envelope proteins or synthetic peptides and whole inactivated viruses from several virulent arboviruses including Chikungunya, Crimean-Congo hemorrhagic fever (CCHF), dengue, tickborne encephalitis and West Nile viruses. We also analyzed sequence data and secondary structures for commonalities that might reveal consensus binding sites among the various aptamers. Some of the highest affinity and most specific aptamers in the down-selected libraries were demonstrated to have diagnostic utility in lateral flow chromatographic assays and in a fluorescent aptamer-magnetic bead sandwich assay. Some of the reported aptamers may also be able to bind viral envelope proteins in vivo and therefore may have antiviral potential in passive immunity or prophylactic applications.

RESULTS

Several arbovirus DNA aptamer sequences emerged multiple times in the various down selected aptamer libraries thereby suggesting some consensus sequences for binding arbovirus envelope proteins. Screening of aptamers by enzyme-linked aptamer sorbent assay (ELASA) was useful for ranking relative aptamer affinities against their cognate viral targets. Additional study of the aptamer sequences and secondary structures of top-ranked anti-arboviral aptamers suggest potential virus binding motifs exist within some of the key aptamers and are highlighted in the supplemental figures for this article. One sequence segment (ACGGGTCCGGACA) emerged 60 times in the anti-CCHF aptamer library, but nowhere else in the anti-arbovirus library and only a few other times in a larger library of aptamers known to bind bacteria and rickettsia or other targets. Diagnostic utility of some of the aptamers for arbovirus detection in lateral flow chromatographic assays and a fluorescent sandwich assay on the surface of magnetic microbeads is also demonstrated.

CONCLUSIONS

This article catalogues numerous DNA aptamer sequences which can bind various important pathogenic arboviruses and have, in some cases, already demonstrated diagnostic potential. These aptamer sequences are proprietary, patent-pending, and partially characterized. Therefore, they are offered to the scientific community for potential research use in diagnostic assays, biosensor applications or for possible passive immunity and prophylaxis against pathogenic viruses.

Healthy individuals' immune response to the Bulgarian Crimean-Congo hemorrhagic fever virus vaccine

Crimean-Congo hemorrhagic fever virus (CCHFV) poses a great threat to public health due to its high mortality and transmission rate and wide geographical distribution. There is currently no specific antiviral therapy for CCHF. This study provides the first in-depth analysis of the cellular and humoral immune response in healthy individuals following injection of inactivated Bulgarian vaccine, the only CCHFV vaccine available at present. Vaccinated individuals developed robust, anti-CCHFV-specific T-cell activity as measured by IFN-γ ELISpot assay. The frequency of IFN-γ secreting T-cells was 10-fold higher in individuals after vaccination with four doses than after one single dose. High levels of CCHFV antibodies were observed following the first dose, but repeated doses were required to achieve antibodies with neutralizing activity against CCHFV. However, the neutralizing activity in these groups was low.

Mice orally immunized with a transgenic plant expressing the glycoprotein of Crimean-Congo hemorrhagic fever virus

While Crimean-Congo hemorrhagic fever (CCHF) has a high mortality rate in humans, the associated virus (CCHFV) does not induce clinical symptoms in animals, but animals play an important role in disease transmission to humans. Our aim in this study was to examine the immunogenicity of the CCHFV glycoprotein when expressed in the root and leaf of transgenic plants via hairy roots and stable transformation of tobacco plants, respectively. After confirmatory analyses of transgenic plant lines and quantification of the expressed glycoprotein, mice were either fed with the transgenic leaves or roots, fed the transgenic plant material and injected subcutaneously with the plant-made CCHFV glycoprotein (fed/boosted), vaccinated with an attenuated CCHF vaccine (positive control), or received no treatment (negative control). All immunized groups had a consistent rise in anti-glycoprotein IgG and IgA antibodies in their serum and feces, respectively. The mice in the fed/boosted group showed a significant rise in specific IgG antibodies after a single boost. Our results imply that oral immunization of animals with edible materials from transgenic plants is feasible, and further assessments are under way. In addition, while the study of CCHF is challenging, our protocol should be further used to study CCHFV infection in the knockout mouse model and virus neutralization assays in biosafety level 4 laboratories.

An update on crimean congo hemorrhagic Fever

Crimean Congo hemorrhagic fever (CCHF) is one of the deadly hemorrhagic fevers that are endemic in Africa, Asia, Eastern Europe, and the Middle East. It is a tick-borne zoonotic viral disease caused by CCHF virus of genus Nairovirus (family Bunyaviridae). CCHF not only forms an important public health threat but has a significant effect on the healthcare personnel, especially in resource-poor countries. India was always a potentially endemic area until an outbreak hit parts of Gujarat, taking four lives including the treating medical team. The current review is an attempt to summarize the updated knowledge on the disease particularly in modern era, with special emphasis on nosocomial infections. The knowledge about the disease may help answer certain questions regarding entry of virus in India and future threat to community.

Epidemiological survey of Crimean-Congo hemorrhagic fever virus in Yunnan, China, 2008

OBJECTIVES

We aimed to determine the seroprevalence of Crimean-Congo hemorrhagic fever virus (CCHFV) infection in Yunnan Province, China.

MATERIALS AND METHODS

One thousand six hundred and fifty-seven human serum samples and 1280 ticks (Hyalomma asiaticum) were collected from five counties (Menglian, Menghai, Lancang, Mengla, and Ximeng). Serum samples were analyzed independently by indirect immunofluorescence assay and Western blotting to detected CCHFV antibody. The ticks were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) to detect virus RNA.

RESULTS

The CCHFV IgG positivity was 3.4% (57/1657). A multivariate analysis was performed, and variables that increased the chance of infection were found to include history of tick bite or contact (odds ratio (OR) 16.6, 95% confidence interval (CI) 7.5-37.0) and age>30 years (OR 6.8, 95% CI 1.6-28.2). The RT-PCR positive rate for ticks was 14.3% (6/42).

CONCLUSIONS

The five counties (Menglian, Menghai, Lancang, Mengla, and Ximeng) in Yunnan are areas with the potential for CCHF outbreaks. Residents should protect themselves against tick bites and the surveillance of CCHFV in this region should be improved.

Recent progress in molecular biology of Crimean-Congo hemorrhagic fever

Crimean-Congo hemorrhagic fever (CCHF) is a severe hemorrhagic fever in humans with a case fatality rate of up to 50%. A causative agent of CCHF is CCHF virus, which is a tick-borne virus in the family Bunyaviridae, genus Nairovirus. The virus is transmitted to humans through infected tick bites, squashed ticks or from direct contact with viremic animals or humans. Outbreaks of CCHF have been documented in Africa, the Middle East, Eastern Europe and Western Asia where the vector and/or reservoir ticks of Hyalomma spp. are distributed. Recent advances in molecular and biochemical analyses of CCHF virus revealed that the virus encodes larger proteins compared to other genus of Bunyavirus and the processing of viral proteins are complicated. Recent studies also showed that the CCHF viruses are relatively divergent in its genome sequence and the viruses are grouped in seven different clades. In general, these phylogenetic analyses based on sequences of S-RNA and L-RNA segment of CCHF viruses indicate that the seven clades correlate with their geographical location. The phylogenetic topology based on M-RNA segment sequences of CCHF viruses is different from those based on S-RNA and L-RNA segments. These analyses indicate that M-RNA segment reassortment events occur more frequently than those in S- and L-RNA segments.

Identification of a novel C-terminal cleavage of Crimean-Congo hemorrhagic fever virus PreGN that leads to generation of an NSM protein

The structural glycoproteins of Crimean-Congo hemorrhagic fever virus (CCHFV; genus Nairovirus, family Bunyaviridae) are derived through endoproteolytic cleavage of a 1,684-amino-acid M RNA segment-encoded polyprotein. This polyprotein is cotranslationally cleaved into the PreGN and PreGC precursors, which are then cleaved by SKI-1 and a SKI-1-like protease to generate the N termini of GN and GC, respectively. However, the resulting polypeptide defined by the N termini of GN and GC is predicted to be larger (58 kDa) than mature GN (37 kDa). By analogy to the topologically similar M segment-encoded polyproteins of viruses in the Orthobunyavirus genus, the C-terminal region of PreGN that contains four predicted transmembrane domains may also contain a nonstructural protein, NSM. To characterize potential PreGN C-terminal cleavage events, a panel of epitope-tagged PreGN truncation and internal deletion mutants was developed. These constructs allowed for the identification of a C-terminal endoproteolytic cleavage within, or very proximal to, the second predicted transmembrane domain following the GN ectodomain and the subsequent generation of a C-terminal fragment. Pulse-chase experiments showed that PreGN C-terminal cleavage occurred shortly after synthesis of the precursor and prior to generation of the GN glycoprotein. The resulting fragment trafficked to the Golgi compartment, the site of virus assembly. Development of an antiserum specific to the second cytoplasmic loop of PreGN allowed detection of cell-associated NSM proteins derived from transient expression of the complete CCHFV M segment and also in the context of virus infection.

Crimean-Congo hemorrhagic fever virus genomics and global diversity

Crimean-Congo hemorrhagic fever (CCHF) is a severe illness with high case fatality that occurs in Africa, Europe, the Middle East, and Asia. The complete genomes of 13 geographically and temporally diverse virus strains were determined, and CCHF viruses were found to be highly variable with 20 and 8%, 31 and 27%, and 22 and 10% nucleotide and deduced amino acid differences detected among virus S (nucleocapsid), M (glycoprotein), and L (polymerase) genome segments, respectively. Distinct geographic lineages exist, but with multiple exceptions indicative of long-distance virus movement. Discrepancies among the virus S, M, and L phylogenetic tree topologies document multiple RNA segment reassortment events. An analysis of individual segment datasets suggests genetic recombination also occurs. For an arthropod-borne virus, the genomic plasticity of CCHF virus is surprisingly high.