Search Results (444)

Torque Teno Virus (TTV), a common and genetically diverse component of the human virome, is not linked to any known disease but reflects immune status. Its plasma viral load has shown clinical relevance in solid organ transplant recipients, correlating it with immunosuppression when present at high levels. However, the clinical significance of TTV viral load in hematopoietic stem cell transplantation (HSCT) recipients is less understood. This systematic review aims to evaluate whether plasma TTV DNA load directly correlates with the degree of T-cell immune reconstitution after HSCT, supporting its potential role as a biomarker for immune competence. The study protocol was registered in the PROSPERO International Prospective Register of Systematic Reviews (CRD420251116208) and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Twenty-one studies were included. The results showed concordant data about TTV kinetics with peak levels reaching approximately between +90 to +120 days after transplantation. Contradictory results have instead been found for the association of TTV load with immune parameters (lymphocyte counts, viral opportunistic infection, and development of acute graft versus host diseases). Even if a low-risk bias assessment was classified in most studies (67%), it was possible to identify important clinical and methodological differences between them, which might account for the different findings observed. Therefore, future larger studies with standardized protocols are needed to assess whether TTV viral load can serve as a reliable tool for guiding clinical decisions in the context of HSCT. Full article

The SARS-CoV-2 nucleocapsid protein (Np) is essential for viral RNA replication and genomic RNA packaging. Phosphorylation of Np within its central Ser-Arg-rich (SRR) linker is proposed to modulate these functions. To gain mechanistic insights into these distinct roles, we performed in vitro biophysical and biochemical studies using recombinantly expressed ancestral Np and phosphomimetic SRR variants. Limited-proteolysis showed minor cleavage differences between wild-type (WT) and phosphomimetic Np, but no major structure or stability changes in the N- and C-terminal domains were observed by circular dichroism spectroscopy and differential scanning fluorimetry, respectively. Mass photometry (MP) revealed that WT Np dimerized more readily than phosphomimetic variants. Crosslinking-MP showed that WT Np formed discrete complexes on viral 5′ UTR stem-loop (SL) 5 RNA, whereas phosphomimetic Np assembled preferentially on SL1–4. WT Np bound non-specifically to all RNAs tested primarily via hydrophobic interactions, whereas phosphomimetic Np showed selectivity for SARS-CoV-2-derived RNAs despite binding more electrostatically. A major difference was observed in the binding kinetics; WT Np compacted and irreversibly bound single-stranded DNA, whereas phosphomimetic Np displayed reduced compaction and fast on/off binding kinetics. These mechanistic insights support a model where phosphorylated Np functions in RNA replication and chaperoning, while non-phosphorylated Np facilitates genomic RNA packaging. The findings also help to explain infectivity differences and clinical outcomes associated with SRR linker variants. Full article

Background: Parvovirus B19 (B19V; Erythroparvovirus primate 1) is now the most commonly detected virus in human endomyocardial biopsies from patients with myocarditis or dilated cardiomyopathy; however, its true causal role remains uncertain. By contrast, Protoparvovirus carnivoran 1, also known as canine parvovirus type 2 (CPV-2), is an apparent cause of myocarditis in neonatal puppies, where it replicates in cardiomyocytes, induces extensive cell death, and often leaves fibrotic scars in survivors. Conclusions: This review compares B19V and CPV-2 from basic biology to clinical expression. Divergent tropism and replication kinetics produce distinct injury patterns: predominantly endothelial and microvascular dysfunction with immune-mediated damage in adult human B19V infection versus direct, age-restricted cardiomyocyte lysis in neonatal CPV-2 infection, often followed by fibrosis. Because parvoviral DNA can persist in cardiac tissue, detection alone does not prove causality. We advocate an “evidence bundle” integrating viral load by quantitative polymerase chain reaction (qPCR), detection of viral transcripts and/or proteins when feasible, spatial co-localization with histological injury, and concordant clinical markers (cardiac troponins and advanced imaging, including cardiac magnetic resonance imaging [CMR]) to support etiologic attribution and guide management in human and veterinary cardiology. Full article

The continuing spread of SARS-CoV-2 and the associated morbidity and mortality, especially in vulnerable populations, highlight the need for the development of antiviral therapeutics. Reverse genetics systems and reporter viruses are valuable for antiviral screening by simplifying methods to detect and quantify virus infections. This study aimed to generate wild-type and Nluc reporter full-length SARS-CoV-2 molecular clones and viruses as tools for high-throughput antiviral assays. The large SARS-CoV-2 genome (~30 kb) makes cDNA cloning and virus rescue technically challenging, so we opted to use cDNA chemical synthesis services to generate full-length wild-type and reporter Delta and Omicron clones. Clone-derived Delta and Omicron wild-type and reporter viruses were successfully rescued and showed replication kinetics comparable to patient-derived isolates. Nluc reporter viruses displayed stable luciferase expression that correlated with viral titres, supporting their reliability as replication substitutes. Antiviral assays measuring replication inhibition by Remdesivir, Molnupiravir, and Nirmatrelvir, based on Nluc expression, yielded IC₅₀ values and selectivity indices consistent with published ranges. Finally, Delta Nluc viruses replicated in primary human bronchial epithelial cells, demonstrating the application of clone-derived viruses in physiologically relevant models. The SARS-CoV-2 cDNA clones and Nluc reporter viruses derived from DNA synthesis services provide a rapid, scalable reverse genetics platform for generating new viruses and developing assays to rapidly assess antiviral compounds against current and emerging SARS-CoV-2 variants or coronaviruses that may emerge in the future. Full article

The GI.3 norovirus is the most detected and recombinant-rich genotype within genogroup I, yet the mechanistic basis for its epidemiological success remains poorly understood. This study integrates Bayesian evolutionary analysis with in vitro enzymology to investigate the link between RdRp function and the evolutionary dynamics of GI.3 NoV. We analyzed 831 GI.3 sequences, finding that prevalent strains (GI.3[P3] and GI.3[P13]) exhibited significantly higher evolutionary rates in both the RdRp and VP1 genes than non-prevalent strains (GI.3[P10] and GI.3[P14]). While the RdRp gene displayed a strong molecular clock signal, the VP1 gene’s evolution was more complex, showing cluster-specific trends. Functionally, the RdRps from prevalent strains demonstrated superior enzymatic activity and substrate affinity (K_m: GI.3[P13] = 0.092 mM; GI.3[P3] = 0.176 mM) compared to non-prevalent strains (K_m: GI.3[P14] = 0.273 mM). Notably, GI.3 RdRp required higher manganese ion concentrations for optimal activity than previously reported for GII strains, suggesting a potential biochemical constraint. Our findings demonstrate a clear correlation between RdRp enzymatic efficiency, evolutionary rate, and strain prevalence. We propose that a highly active RdRp may potentially accelerate VP1 evolution and confer a replicative advantage, underpinning the dominance of specific GI.3 lineages. This work provides crucial experimental evidence linking viral polymerase function to evolutionary and epidemiological outcomes. Full article

Background: Two natural steroids derived from cholesterol pathways are testosterone and progesterone, androgen and antiandrogen receptor binding. Steroid androgen antagonists can be prescribed to treat an array of diseases and disorders such as gender dysphoria. In men, androgen antagonists are frequently used to treat prostate cancer and hyperplasia. Sex hormones regulate the expression of the viral receptors in COVID-19 progression, and these hormones may act as a metabolic signal-mediating response to changes in glucose and Reactive Oxygen Species (ROS). The objective of the present study is to use artificial intelligence (AI) applications in healthcare to predict the targets and to assess biological assays of novel steroid derivatives prepared in house from the commercially available 16-dehydropregnenolone acetate (DPA^®) aimed at achieving the metabolic stability of glucose and steroid brain homeostasis. This suggests the introduction of aromatic or aliphatic structures in the steroid B-ring and D-ring. This is important since the roles of 5α-reductase and ROS in brain control of glucose and novel steroids homeostasis remain unclear. Methods: A tool prediction was used as a tuned algorithm, with the novel steroid derivatives data in web interface to carry out their pharmacological evaluation. The new steroidal derivatives were determined with neuroprotection effect using the select biomarkers of oxidative stress on induced hypoglycemic male rat brain and liver. The enzyme kinetics was established by the inhibition of the 5α-reductase enzyme on the brain myelin. Results: We used novel chemical structures to order the information of a Swiss data bank that allow target predictions. Biological assays suggest that steroid derivatives with an electrophilic center can interact more efficiently with the 5α-reductase enzyme, and by this way, induce neuroprotection in hypoglycemia model. All compounds were synthesized with a yield of 30–80% and evaluated with tool target prediction to understand the molecular mechanisms underlying a given phenotype or bioactivity and to rationalize possible favorable or unfavorable side effects, as well as to predict off-targets of known molecules and to clear the way for drug repurposing. Apart, they turned out to be good inhibitors for the 5α-reductase enzyme. Conclusions: The probed efficacy of these novel steroids with respect to spironolactone control appears to be a promising compound for future hormonal therapy with neuroprotection activity in glucose disorder status. However, further research with clinically meaningful endpoints is needed to optimize the use of androgen antagonists in these hormonal therapies in COVID-19 progression. Full article

Efficient reverse genetics systems are essential for understanding SARS-CoV-2 pathogenesis, host–virus interactions, and potential therapeutic interventions. Here, we developed a cost-effective PCR-based reverse genetics platform that splits the SARS-CoV-2 genome into only six bacterial plasmids, enabling cloning, manipulation, and the rescue of recombinant SARS-CoV-2 (rSARS-CoV-2) with high fidelity and high viral titers after a single passage. Using this system, we generated and characterized spike protein mutants Y453F and N501Y, as well as a U76G mutation in the 5′-UTR. Y453F showed reduced replication kinetics, lower cell binding, and diminished fitness, while N501Y exhibited comparable replication and fitness, highlighting the distinct effects of these spike protein mutations. The U76G mutation is located within a novel NSP9 binding site in the 5′-UTR and leads to impaired RNA synthesis and reduced viral replication efficiency, suggesting an important role in transcription and replication. Our findings highlight the robustness and adaptability of this reverse genetics system, providing a versatile, cost-effective tool for studying SARS-CoV-2 mutations and their effects on replication and fitness, with potential applications in vaccine and therapeutic development. Full article

Feline herpesvirus-1 (FHV-1) is taxonomically classified within the family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus, and species Felid alphaherpesvirus 1. The genome of FHV-1 is 135,797 bp in length and encodes 74 proteins. Among these proteins, serine/threonine protein kinase (pK) and thymidine kinase (TK) have been identified as potential virulence factors in alphaherpesviruses, although these kinases are dispensable for viral replication. As kinases, regulating phosphorylation modification is one of their functions, while the mechanism by which phosphorylation modification affects cell physiological functions and thereby influences viral replication remains unclear. In this study, we generated pK- and TK-deficient FHV-1 mutants by CRISPR/Cas9-mediated homologous recombination. The pK-deficient virus produced significantly smaller plaques than the TK-deficient virus. The replication kinetics of the pK-deficient virus were attenuated in multistep growth compared to the TK-deficient virus. These results indicate that deletion of the pK gene markedly reduces the replicative capacity of FHV-1. We applied data-independent acquisition (DIA) quantitative proteomics to profile changes in global protein expression and phosphorylation in F81 cells upon infection with TK⁻, pK^−, and wild-type FHV-1 strain. The pK-deficient virus exhibited 3632 differentially phosphorylated proteins containing 11,936 modification sites; the TK-deficient virus showed 4529 differentially phosphorylated proteins with 19,225 phosphorylation sites. Functional characterization through Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses identified significant involvement of phosphoproteins in spliceosome pathways in pK-deficient virus and ATP-dependent chromatin remodeling pathway in TK-deficient virus. Notably, several splicing regulators—including Ess-2 and CDK13, which modulate host spliceosomal function—displayed significantly reduced phosphorylation levels in pK-deficient viruses. A significant enrichment of ATP-dependent factors, such as SMARCA5 and RSF1, was observed in the TK-deficient virus. To our knowledge, this is the first investigation into the effects of FHV-1 infection on the host cell phosphoproteome. These data offer new insights into the phosphoregulatory circuits and signaling networks triggered by FHV-1 and may enhance our understanding of the FHV-1 replication mechanism. Full article

Plant protease inhibitors (PPI) play a significant role against microbes, insects, and, to a considerable extent, human pathogens. PPIs inactivate hydrolase enzymes or depolarize the plasma membrane of the pathogens, thereby inhibiting their growth, replication, and invasion. Here, an active serine protease inhibitor was isolated and purified from the seeds of Cleome viscosa. The purified inhibitor was homogenous and exhibited a molecular weight of around 12 kDa as a monomer. The secondary structure analysis indicated that the inhibitor was predominantly composed of α-helical content. The kinetics experiments demonstrated a noncompetitive mode of inhibition towards serine protease when casein was used as the enzyme substrate. The inhibitor formed a stable complex with serine protease, having a likely 1:1 stoichiometry, as inferred from ITC, and the dissociation constant was examined to be K_d = 1.9 × 10⁻⁶ M with a Gibbs free energy of ΔG = −8.079 (kcal/mol). The inhibitor exhibits stable protease inhibition up to 90 °C. Further, in vitro preliminary studies revealed its inhibitory effects against HSV-2 function, evidence that it may have a role in the treatment of viral infections. Full article

This study investigates the production of volatile organic compounds (VOCs) in RK-13 cells infected with three equine viruses representing different families: equine arteritis virus (EAV) (Arteriviridae), equine herpesvirus 1 (EHV-1) (Herpesviridae), and equine rhinitis B virus (ERBV) (Picornaviridae). VOCs, which are byproducts of cellular metabolism and potential non-invasive diagnostic markers, were analyzed using headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC-MS). Since viruses do not possess intrinsic metabolic activity, the observed changes in the VOC profiles were attributed to host responses, such as metabolic reprogramming, oxidative stress, and apoptosis. We hypothesized that each viral infection induces distinct metabolic changes, resulting in characteristic VOC signatures that mirror the virus type, replication kinetics, and cytopathic effects. Notably, viruses with rapid cytopathic effects (e.g., EHV-1) were anticipated to trigger more pronounced VOC alterations. In our experimental design, RK-13 cells were infected at a multiplicity of infection of 1 and incubated for 24 h, 48 h, or 72 h. Distinct VOC profiles emerged, with significant elevations in compounds like 2-ethyl-1-hexanol, particularly in EHV-1 infections, and selective increases in acetophenone and benzaldehyde. Principal component analysis (PCA) of the VOC concentration data showed the clear separation of data from viruses from different families. These findings support the potential of VOC profiling as a rapid diagnostic tool for viral infections. Full article

ZIKA virus (ZIKV) infections in human neonates and adults are associated with deleterious effects on brain cognition and neurological disorders. The mechanism(s) of ZIKV infection in neurons and associated neuronal antiviral responses are not fully understood. In this study, we determined the effects of ZIKV infectivity in human neuronal (SH-SY5Y) cells and mouse N2a cells/primary cultures of murine cortical neurons at early and late tested timepoints of infection. The human neuronal cells had higher ZIKV loads compared to the mouse N2a cells, but the viral loads in the murine cortical neurons were between the loads in these two in vitro cell lines. The murine cortical neurons were thought to be more permissive to ZIKV infection, but viral infection kinetics showed a declining trend like that observed in the mouse N2a cells. We noted that infectious extracellular vesicle (EV)-mediated ZIKV infection showed higher viral loads in the SH-SY5Y cells compared to direct infection with laboratory virus stocks. Similar results were obtained with ZIKV infectious EVs in the mouse N2a cells and cortical neurons. In addition, we noted that ZIKV infection significantly induced EV secretion from all three neuronal cells. Also, we found that ZIKV infection modulates the expression of type 1 interferons (IFNs) and entry receptors such as Tyro3, Axl, and MER-TK (TAM). Alongside the increased ZIKV loads in the SH-SY5Y cells, IFN-beta transcript levels and receptors Tyro3/MER-TK were upregulated at early timepoints of infection. Overall, the reduced ZIKV loads and decreasing IFN expression in the mouse neuronal cells suggested a unique murine cellular ability to restrict and limit viral replication. This could be one of the reasons for the unavailability of wild-type mouse models for ZIKV infection. Our data further shows that ZIKV may preferentially infect human rather than murine neuronal cells, and this could be the potential reason for microcephaly in newborns. Full article

Influenza reporter viruses are essential for studying viral infection dynamics and assessing antiviral drug efficacy. However, insertion of exogenous reporter genes can impair both viral replication and reporter expression, limiting the development of these systems. In this study, CE1 compensatory mutation (G3A/C8U) was introduced into the 3′ non-coding region of the NS segment of influenza A/Puerto Rico/8/1934 using reverse genetics, generating the recombinant reporter virus H1N1-PR8-NS_CE1-mCherry. Compared with H1N1-PR8-NS_WT-mCherry, H1N1-PR8-NS_CE1-mCherry produced approximately 2.7-fold more infectious particles. CE1 compensatory mutation partially restored impaired replication kinetics in vitro, as evidenced by higher titers of H1N1-PR8-NS_CE1-mCherry at 48 h post-infection in MDCK cells. Additionally, H1N1-PR8-NS_CE1-mCherry maintained the intact mCherry gene insertion and high viral titers during serial passaging. Additionally, a real-time, non-invasive in vivo imaging of influenza A viruses was established using H1N1-PR8-NS_CE1-mCherry. A significant correlation was observed between lung fluorescence intensity and viral load, indicating that fluorescence signals serve as a reliable indicator of lung viral load in infected mice. Finally, utility of this model for in vivo drug screening was confirmed by antiviral drug oseltamivir phosphate. Above all, H1N1-PR8-NS_CE1-mCherry provides a tool for visualizing influenza A virus infection and evaluating antiviral drug efficacy. Full article

African swine fever (ASF) continues to spread across the globe, causing a severe impact on the swine industry. Passive surveillance based on testing dead pigs is one of the most effective methods for early detection of ASF incursions. We have previously shown that the superficial inguinal lymph node (SILN) is a convenient and effective sample type for ASF virus (ASFV) genome detection in pigs succumbed to highly or moderately virulent ASFV infections. In this study, we explored the distribution kinetics of ASFV into SILN and other lymphoid tissues in pigs exposed to moderately virulent ASFV strains (ASFV Estonia 2014 and ASFV Malta’78), oronasally. The ASFV genome was detected in SILNs as early as 2–3 days post-infection (dpi), peaking around 5–9 dpi. The detection of ASFV Estonia 2014 started early, and the pigs succumbed to infection faster compared to the ASFV Malta’78 infected pigs that remained longer. All pigs that succumbed to ASF had comparable levels of ASFV genomic material in the spleen and SILNs. The levels of ASFV genomic material gradually started to decrease in pigs that did not succumb to ASF, indicating possible virus clearance. In contrast, ASFV genome levels in blood and spleen samples remained relatively steady during the study period. Immunohistochemistry and in situ hybridization of spleen and SILN samples supported real-time PCR results. This study demonstrates the distribution kinetics of moderately virulent ASFV in peripheral lymph nodes and highlights the utility of SILNs for dead pig screening. Full article

Background: Understanding the immune mechanisms that differentiate protective from pathogenic responses during dengue virus (DENV) infection is critical for effective vaccine development. Objective: To investigate how CD4⁺ T cell depletion alters viral control and the humoral immune response during primary DENV2 infection in a non-human primate (NHP) model. Methods: Rhesus macaques were depleted of CD4⁺ T cells prior to DENV2 infection. Viral kinetics, B cell activation, antibody specificity, and functional outcomes were evaluated longitudinally, including cross-reactivity and antibody-dependent enhancement (ADE) potential. Results: CD4⁺ T cells were essential for early viral clearance and the generation of robust, type-specific neutralizing antibodies. In their absence, animals exhibited early non-specific polyclonal B cell activation, delayed isotype switching, and an expanded repertoire of cross-reactive antibodies to DENV and Zika virus (ZIKV), with diminished neutralizing capacity. CD4-depleted macaques also showed increased ADE potential, particularly against ZIKV, and elevated anti-NS1 IgG titers that persisted one-year post-infection. Conclusion: CD4⁺ T cells play a critical role in orchestrating effective, durable, and type-specific antibody responses during primary DENV infection. Their absence leads to delayed antibody maturation, greater cross-reactivity, and higher ADE potential. These findings emphasize the need for DENV and ZIKV vaccines to include CD4⁺ T cell epitopes that promote high-quality, type-specific antibody responses and minimize ADE risk. Full article

Early studies on the evolution of SARS-CoV-2 revealed mutations that favored host transmission of the virus and more efficient viral entry. However, cell-free virus spread is vulnerable to host-neutralizing antibodies. As population immunity developed, mutations that confer escape from neutralization were selected. Notably, cell syncytia formation wherein an infected cell fuses with a noninfected cell is a more efficient route of transmission that bypasses humoral immunity. Cell syncytia formation has been implicated in the pathogenicity of SARS-CoV-2 infection whilst compromising host transmission due to impaired whole virion release. Therefore, understanding the mechanisms of virus-mediated cell–cell fusion will aid in identifying and targeting more pathogenic strains of SARS-CoV-2. Whilst the general kinetics of cell–cell fusion have been known for decades, the specific mechanisms by which SARS-CoV-2 induces fusion are beginning to be elucidated. This is partially due to emergence of more reliable, high throughput methods of quantifying and comparing fusion efficiency in experimental models. Moreover, the ongoing inflammatory response and emerging health burden of long COVID may point to cell–cell fusion in the pathogenesis. In this review, we synthesize current understanding of SARS-CoV-2-mediated cell–cell fusion and its consequences on immune escape, viral persistence, and the innate immune response. Full article