Search Results (159)

Dengue Virus (DENV) circulates as four antigenically distinct serotypes whose dominance fluctuates over time in many endemic regions, a phenomenon known as serotype shift that is frequently associated with large outbreaks and increased disease severity. This review, through a synthesis of epidemiological, virological, immunological, entomological, and environmental evidence, observes that serotype shift likely arises from the interaction of multiple determinants rather than solely from viral evolution, with population immunity playing a central role. The accumulation of serotype-specific herd immunity, together with short-lived cross-protection and Antibody-Dependent Enhancement (ADE), reshapes population susceptibility and creates ecological space for heterologous serotypes with higher transmission potential. The synthesis of global dengue studies indicates that these immune dynamics interact with viral genetic diversity, vector competence, climate variability, and human factors such as demography, socioeconomic status, population density and mobility to drive cyclical and sometimes abrupt changes in serotype dominance. Notably, the review indicates that serotype changes often precede or coincide with more clinical severity and patterns of outbreaks, with direct implications for the process of forecasting outbreaks, vaccine performance, and preparedness to respond with appropriate health measures. On the whole, this review confirms the opinion that the change of dengue serotype occurrence becomes a consequence of interconnected biological and ecological processes involved in the transmission of dengue serotype shifts in hyperendemic areas. Full article

Different protozoan parasites are the causative agents of tropical diseases, including malaria, toxoplasmosis, leishmaniasis, and Chagas disease (CD), which, altogether, affect over 300 million people throughout the world. Except for two recently approved malaria vaccines, individuals affected by or at risk of contracting any of these four diseases still experience a lack of effective treatments and vaccines. Many vaccine studies, including those that have reached clinical trials, are based on inactivated parasites, adjuvanted recombinant proteins, or viral vector vaccines. Here, we review the current advances towards the development of vaccines based on genetically modified live-attenuated parasites (GMLAP) as well as RNA formulations encoding parasite antigens. Because these are diseases caused by intracellular pathogens that depend on efficient T-cell responses for parasite control, these two new vaccine platforms have generated great expectations, since they are known to induce a robust cellular immune response. Although preclinical studies aimed at developing new malaria, toxoplasmosis, and leishmaniasis vaccines have led to significant progress that may soon result in clinical trials, advances in next-generation vaccines against CD are lagging behind. Increased collaborative efforts between research groups, governments, and the pharmaceutical industry, particularly in Africa, Asia, and Latin American countries, are urgently needed to accelerate the development of vaccines for all neglected and less-studied diseases. Full article

Background/Objectives: The emergence of SARS-CoV-2 variants and breakthrough infections underscores the need for next-generation vaccines capable of protecting from natural infection and/or preventing virus transmission. Intranasal vaccination offers a promising approach by eliciting local immune responses in the nasal mucosa, the primary site of infection and reservoir for transmissible virus. We evaluated two live-attenuated, respiratory syncytial virus-vectored vaccines in which the RSV F and G surface glycoproteins were replaced with a chimeric SARS-CoV-2 Spike protein from the ancestral USA/WA-1/2020 strain (MV-014-212) or the Delta variant (MV-014-212-delta). Methods: K18-hACE2 mice and LVG Syrian hamsters were vaccinated with a single intranasal dose of MV-014-212 or MV-014-212-delta. Systemic and mucosal immunity were assessed following vaccination, and protection was evaluated following Delta SARS-CoV-2 challenge. In vaccinated hamsters, morbidity, viral shedding, and lung inflammation and injury were also assessed following natural exposure to infected cagemates. Results: A single intranasal dose of either vaccine elicited systemic and mucosal immunity in K18-hACE2 mice, including serum neutralizing antibodies, Spike-specific memory B cells and plasmablasts, and Spike-specific CD8⁺ lung-resident memory T cells. Although MV-014-212-delta vaccination provided the best protection against the Delta variant virus challenge, both vaccines decreased viral loads in nasal discharge, lung, and brain, and reduced weight loss and mortality. In naturally acquired infection studies, vaccinated hamsters exposed to infected cagemates exhibited minimal weight loss, limited viral replication within the nasal mucosa, and attenuated lung pathology. Conclusions: Intranasal RSV-vectored vaccines can elicit broad protective respiratory immunity, suggesting that this platform could be leveraged for other respiratory pathogens. Full article

Background/Objectives: Bovine viral diarrhea (BVD) is a major infectious disease of cattle caused by bovine viral diarrhea virus genotypes 1 and 2 (BVDV-1 and BVDV-2). Current inactivated and live attenuated vaccines provide incomplete cross-genotype protection and may exhibit limitations related to durability of immunity or safety. This study evaluated whether co-expression of the BVDV envelope glycoproteins E1 and E2 in a Modified Vaccinia Ankara (MVA) vector could support antigen expression and induce immune responses in a proof-of-concept model. Methods: Recombinant Modified Vaccinia Ankara (MVA) viruses expressing BVDV-1 E1E2 or BVDV-2 E1E2 were generated by homologous recombination. Recombinant viruses were purified and characterized for antigen expression, genetic stability, and growth properties in vitro. Immunogenicity was evaluated in a BALB/c mouse model by measuring E2-specific antibody responses, virus-neutralizing antibodies, and antigen-responsive cellular immune responses. Results: Both recombinant MVA constructs showed detectable E2 expression when E1 and E2 were co-expressed, and exhibited growth characteristics comparable to parental MVA with stable maintenance after serial passage. In contrast, recombinant MVA expressing E2 alone did not yield detectable E2 protein under the same experimental conditions. Immunization induced detectable humoral and cellular immune responses, including E2-specific IgG antibodies, virus-neutralizing antibodies, and increased frequencies of antigen-responsive CD8⁺ T cells with a tendency toward a Th1-biased profile. Conclusions: These findings indicate that co-expression of BVDV E1 and E2 in an MVA vector can support detectable antigen expression and induce measurable immune responses in a mouse proof-of-concept model. Further studies in cattle, including challenge experiments, will be required to determine the protective efficacy and practical applicability of this platform for BVDV vaccine development. Full article

Background: Infectious hematopoietic necrosis virus (IHNV), a rhabdovirus classified within the genus Novirhabdovirus, continues to be one of the most detrimental pathogens impacting salmonid aquaculture on a global scale. Notable for inducing high mortality rates among fry and fingerlings, IHNV represents a substantial threat to the economic stability of the aquaculture industry. This review offers an in-depth analysis of the contemporary advancements in IHNV vaccine development. Methods: We assess the efficacy and immunological mechanisms of traditional vaccine platforms, including inactivated and live-attenuated vaccines, while emphasizing the groundbreaking success of DNA vaccines, particularly those encoding the viral glycoprotein (G). Although nucleic acid-based therapies provide high levels of protection, they face logistical challenges related to delivery and regulatory obstacles associated with Genetically Modified Organisms (GMOs). Additionally, we examine emerging “next-generation” platforms, such as viral vector vaccines, subunit proteins produced in yeast or plant systems, and RNA-based technologies. We critically analyze technical bottlenecks, including the lack of efficient mucosal delivery systems and the limited understanding of long-term cellular memory in teleosts. Results: We propose future research directions that emphasize the development of multivalent formulations and the incorporation of molecular adjuvants to augment mucosal immunity. Conclusions: This synthesis seeks to integrate fundamental viral pathogenesis with applied immunology to develop a strategic framework for the sustainable, long-term management of IHNV in global salmonid populations. Full article

African swine fever (ASF), a highly contagious and lethal viral disease caused by the African swine fever virus (ASFV), poses a severe threat to the global swine industry. Recent outbreaks across Asia, Europe, and the Caribbean are exacerbating the challenge. Current control measures rely mainly on early detection, culling and strict biosecurity practices, underscoring the urgent need for a safe and effective vaccine. Since the mid-1960s, diverse vaccine strategies, including inactivated, subunit, DNA/mRNA, vectored, and live attenuated virus (LAV) vaccines, have been explored. Inactivated vaccines have consistently failed to confer protection due to insufficient functional antigen presentation and weak cellular immune activation. Subunit vaccines targeting single or multiple ASFV antigens have also shown limited success, often failing to induce sterile or long-lasting immunity. Among these approaches, LAV vaccines have demonstrated the greatest promise in eliciting robust and durable immune responses. However, major knowledge gaps remain regarding ASFV biology, ASFV–host interactions, ASFV immune evasion mechanisms, protective and cross-protective immunity, stable cell lines for LAV production, virulence reversion of LAVs, and the lack of harmonized standards for evaluating vaccine safety and efficacy, all of which impede the development of safe and broadly effective ASF vaccines. This narrative review summarizes recent advances in ASF vaccine research and highlights the critical obstacles that must be overcome to achieve successful ASF vaccine development. Full article

Background/Objectives: Chimpanzee adenoviral-vectored vaccines have proven to be both safe and effective, with a manufacturing and distribution pipeline capable of rapid global supply, as demonstrated during the COVID-19 pandemic. Yellow fever is a mosquito-borne viral hemorrhagic disease endemic in parts of Africa and Latin America, and although an effective live attenuated vaccine exists, its use is limited by safety and eligibility restrictions. Moreover, large outbreaks continue to expose critical challenges, such as an insufficient vaccine supply, reliance on fractional dosing, and slow and difficult-to-scale manufacturing processes. Here, we report the design, development and in vivo immunogenicity of multiple yellow fever virus (YFV) antigen constructs based on the pre-membrane (prM) and envelope (E) proteins—with or without the transmembrane domain (TM or ΔTM)—delivered using the ChAdOx1 adenoviral vector. Methods: Four ChAdOx1 YF vaccines were developed, and immunogenicity was evaluated. The efficacy of the full-length YF envelope vaccine was also tested in Balb/c mice. Results/Conclusions: In contrast to previously described orthoflavivirus vaccines on the same platform, the full-length antigen elicited superior immunogenicity and conferred protection against intracranial challenge with the YF17D virus in mice. Notably, this protection was comparable to that induced by the licensed YF17D vaccine, highlighting the promise of this platform as a next-generation yellow fever vaccine candidate. Full article

Background: Members of the virus family Herpesviridae are among the most successful pathogen groups in evolutionary history. They not only pose a serious public health threat to humans but also cause significant economic losses in the global livestock industry. The primary immunological challenge in developing sterilizing vaccines is the lifelong latency of herpesviruses in the nervous system or lymphoid tissues. Methods: This analysis compares the vaccine strategies designed against the five most important Alphaherpesvirinae pathogens: HSV-1/2, PRV, BHV-1, EHV-1/4, and FHV-1. The contrast between the globally licensed veterinary vaccines and the relative stagnation in the field of human HSV vaccines is stark. However, there are notable success stories regarding the implementation of ‘Marker Vaccines’ (DIVA strategies) in veterinary medicine. This review examines various vaccine modalities, assessing their potential to mitigate clinical outbreaks and their shortcomings in preventing viral shedding and establishing latency. Results: This study reveals common technical bottlenecks across species, attributed to immune evasion mechanisms such as the downregulation of MHC I, TAP inhibition, the failure to induce robust mucosal IgA, and safety concerns regarding the recombination of live vectors. Conclusions: This review highlights several promising avenues that could lead to enhanced herpesvirus vaccines and recommends the rational design of T-cell epitopes alongside innovative mucosal adjuvants. Furthermore, it bridges the gap between veterinary and human vaccinology from a One Health perspective, suggesting that lessons learned from veterinary practices could facilitate necessary breakthroughs in human medicine. Full article

Live attenuated Salmonella enterica serovar Typhimurium has been investigated for decades as an orally delivered vaccine vector due to its ability to target the intestinal mucosa and engage both innate and adaptive immune responses. In humans, S. Typhimurium infection is largely restricted to the gastrointestinal tract, distinguishing it from Salmonella Typhi and providing a rationale for its use in mucosal vaccine strategies. In this review, we discuss the biological features of S. Typhimurium that support its use as a vaccine vector and summarize current understanding of the immune responses generated during wild-type infection, including innate activation and downstream T cell and B cell responses. We compare key biological differences between Salmonella Typhi and S. Typhimurium and outline emerging vector design strategies, including delayed attenuation and chromosomal integration of heterologous antigens. We then review applications of attenuated S. Typhimurium vectors targeting viral, bacterial, and parasitic pathogens, highlighting shared immunological outcomes and design principles across platforms. Finally, we discuss recent advances in vector engineering, including chromosomal integration of heterologous antigens, as well as remaining gaps in knowledge related to the durability of immune responses and translational considerations. Full article

Bluetongue (BT) is a noncontagious, arthropod-borne viral disease of domestic and wild ruminants caused by bluetongue virus (BTV), an arbovirus of the Orbivirus genus within the Sedoreoviridae family. At least 36 serotypes have been identified globally; recurrent circulation of BTV-1, -4, and -8, along with the recent emergence of BTV-3 in northern Europe, underscores a persistent incursion risk for Mediterranean herds. Key drivers include climate-driven expansion of Culicoides vector niches, windborne dispersal, animal movements, and subclinical reservoirs in cattle and goats. As no specific treatment is currently available, control of bluetongue disease still relies largely on vaccination. Live-attenuated vaccines and inactivated vaccines have reduced incidence, but important limitations persist: risk of reversion and the possibility of reassortment for LAVs; requirement for multiple doses and limited cross-protection for inactivated products; and the absence of DIVA capability for both. As an alternative, next-generation platforms are under active evaluation. Subunit formulations, often VP2 combined with VP5 and/or NS1/NS2 virus-like particles (VLPs), and viral-vectored constructs demonstrate favorable safety, strong humoral and cellular responses, inherent or engineered DIVA compatibility, and potential for rapid updating against emergent serotypes. This review synthesizes recent bluetongue activity across the Mediterranean Basin and provides a critical assessment of both existing and emerging vaccine strategies, with a focus on recommending next-generation platforms that emphasize DIVA-compliant, multiserotype, and adaptable vaccination approaches, supported by integrated surveillance and vector control in the region. Full article

Arthropod-borne orthoflaviviruses, including dengue, Zika, Japanese encephalitis, yellow fever and West Nile viruses, pose a significant global public health threat, causing hundreds of millions of infections annually with severe clinical symptoms. However, the lack of effective vaccines and antiviral drugs, coupled with the biosafety risks associated with handling live highly pathogenic strains, hinders progress in antiviral research. Pseudovirus technology, which uses single-round infectious viral particles lacking replication competence, has thus gained prominence as a safe and versatile tool for antiviral research. This review systematically summarizes the construction, optimization, and applications of orthoflavivirus pseudoviruses in antiviral research. The primary construction strategies of orthoflavivirus pseudoviruses rely on multi-plasmid co-transfection of viral replicons and structural protein expression vectors, leveraging the host cell secretory pathway to mimic natural viral assembly and maturation. The core applications of pseudovirus technology are highlighted, including high-throughput screening and detection of neutralizing antibodies, identification of antiviral drugs targeting viral entry or replication, and evaluation of vaccine immunogenicity. Despite these strengths, the approach still faces limitations, such as incomplete simulation of native viral structures and batch-to-batch titer variability, which may affect the physiological relevance of findings. In summary, orthoflavivirus pseudovirus technology has become an essential platform in both basic virology research and translational medicine, providing critical insights and tools in the ongoing fight against arthropod-borne orthoflaviviruses diseases. Full article

Recombinant adeno-associated viral vectors (rAAVs) are the leading gene delivery vehicles in clinical development, yet efficient nuclear delivery remains a major barrier to effective transduction. This limitation is partly due to the incomplete understanding of rAAV’s complex subcellular trafficking dynamics. Here, we establish a longitudinal confocal live-cell imaging workflow that tracks rAAV2 from 4 to 12 h post-transduction, paired with an automated 3D analysis pipeline that quantifies spatiotemporal vector distribution, cytoplasmic trafficking, nuclear accumulation, and transgene expression at single-cell resolution. We use this platform to evaluate the effects of vector dose, cell cycle progression, and the behavior of empty particles. We identify previously undescribed trafficking features associated with high transgene expression. Higher rAAV2 doses enhanced cytoplasmic trafficking and nuclear delivery, while cell cycle progression facilitated both trafficking efficiency and transgene expression. We also characterize empty rAAV2 particles, revealing distinct trafficking patterns and markedly reduced nuclear accumulation compared to genome-containing vectors. By uncovering new bottlenecks in rAAV transduction, this platform provides mechanistic insights and potential strategies to improve AAV-based gene therapy. Its generalizable design further supports broad applicability to other non-enveloped viruses. Full article

Epizootic hemorrhagic disease (EHD) is an important livestock disease caused by Epizootic hemorrhagic disease virus (EHDV). The recent incursion and wide distribution of EHDV in Europe have increased the need for effective vaccine candidates. Background/Objectives: The VP2 protein of EHDV forms the outer capsid layer of the virion and is essential for viral assembly and host cell entry. Owing to its antigenic properties, VP2 represents a major target for vaccine development. However, the recombinant production of VP2 is limited by low stability and poor yields, representing a significant barrier for the generation of safe and effective subunit vaccines. Methods: To overcome these limitations, the VP2 protein from EHDV serotype 8 (EHDV-8) was rationally engineered with targeted modifications at both the amino and carboxyl termini of its coding sequence. Recombinant expression was performed using a baculovirus vector-mediated system in Trichoplusia ni pupae (CrisBio^® technology), employed as living biofactories. Results: The engineering of VP2 resulted in up to a tenfold increase in protein yields compared with the wild-type sequence, while maintaining the trimeric structural integrity of the recombinant protein. Both wild-type and engineered VP2 protein variants were formulated and used to immunize IFNAR(−/−) mice, a model susceptible to EHDV infection. Both engineered and wild-type VP2 formulations elicited comparable neutralizing antibody responses in vaccinated animals. Furthermore, immunization with either formulation conferred full protection against lethal EHDV-8 challenge. Conclusions: In this work, we demonstrated that the rational engineering of the VP2 protein significantly improved recombinant expression yields in a baculovirus-based system without compromising structural integrity or immunogenicity. These findings additionally demonstrate the feasibility of producing high-quality VP2 antigens in T. ni pupae using CrisBio^® technology and support their potential application in the development of subunit vaccines against EHDV. Full article

Influenza viruses remain a major global public health concern, causing significant morbidity and mortality annually despite widespread vaccination efforts. The limitations of current seasonal vaccines, including strain-specific efficacy and manufacturing delays, have accelerated the development of next-generation candidates aiming for universal protection. This review comprehensively summarizes the recent progress in universal influenza vaccine research. We first outline the key conserved antigenic targets, such as the hemagglutinin (HA) stem, neuraminidase (NA), and matrix proteins (M2e, NP, and M1), which are crucial for eliciting broad cross-reactive immunity. We then delve into advanced antigen design strategies, including immunofocusing, multi-antigen combinations, computationally optimized broadly reactive antigens (COBRA), and nanoparticle-based platforms. Furthermore, we evaluate evolving vaccine delivery systems, from traditional inactivated and live-attenuated vaccines to modern mRNA and viral vector platforms, alongside the critical role of novel adjuvants in enhancing immune responses. The convergence of these disciplines—structural biology, computational design, and nanotechnology—is driving the field toward a transformative goal. We conclude that the successful development of a universal influenza vaccine will likely depend on the strategic integration of these innovative approaches to overcome existing immunological and logistical challenges, ultimately providing durable and broad-spectrum protection against diverse influenza virus strains. Full article

Background/Objectives: African Swine Fever (ASF), caused by the African Swine Fever Virus (ASFV), is a highly contagious and lethal disease in pigs, for which no recognized safe and effective vaccine is currently available. The ASFV EP153R gene, expressed during both early and late infection stages, exhibits strong protective potential. Utilizing advances in genetic engineering, recombinant PRRSV vector vaccines carrying ASFV exogenous genes were constructed. This study aims to prepare pEP153R-based polyclonal antibodies and an iELISA detection method using the constructed rPRRSV-EP153R as a specific target to verify the iELISA’s specificity and effectiveness. Methods: A prokaryotic plasmid, pCold-TF-EP153R, was constructed to express protein in BL21 (DE3). The purified soluble protein (2 mg/mL) was used to generate a murine polyclonal antibody and establish an indirect ELISA. The EP153R gene was inserted between ORF1b and ORF2a of PRRSV via reverse genetics, yielding recombinant rPRRSV-EP153R. Its biological properties were assessed in vitro and in vivo. Results: The pEP153R was specifically detected by both anti-His antibody and generated polyclonal antibodies. An established iELISA showed high specificity, sensitivity, and 98.18% accuracy. The antibodies specifically recognized pEP153R expressed in recombinant virus and eukaryotic systems. Additionally, the recombinant virus stably maintained EP153R without changes in virological characteristics relative to vHuN4-F112. In vaccinated piglets, the rPRRSV-EP153R induced a specific, consistent, and detectable immune response. Conclusions: The established iELISA, characterized by high specificity, sensitivity, and accuracy, furnishes reliable technical support for the serological diagnosis of ASFV. Meanwhile, the recombinant virus rPRRSV-EP153R demonstrates potential as a novel live vectored vaccine candidate, with the capability to induce specific immunity against both ASFV and PRRSV. Full article