Search Results (6,016)

Klebsiella pneumoniae infection following H9N2 Influenza A virus (IAV) infection causes severe pneumonia. But the underlying pathogenic mechanisms of H9N2 IAV and K. pneumoniae co-infection are complex and need to be further explored. In this study, the lung transcriptomes of mice with H9N2 IAV and K. pneumoniae co-infection were characterized by transcriptomic profiling. As a result, GO enrichment analysis revealed that the differential genes were primarily involved in the activation of immune responses, cellular components of membranes and extracellular spaces, and defense responses against pathogen infections. According to KEGG enrichment, the differentially expressed genes (DEGs) were concentrated in TLR signaling pathways, RLR signaling pathways, TNF signaling pathways and NLRP3 signaling pathways. Furthermore, in vitro cell models were established to investigate the innate immune responses induced by H9N2 IAV and K. pneumoniae CPS co-stimulation. K. pneumoniae CPS stimulation influenced the cytokine profiles of mink lung epithelial cells infected with H9N2 IAV, worsened cell viability, and aggravated apoptosis, indirectly inhibiting H9N2 IAV replication. The findings demonstrated that K. pneumoniae superinfection modulated the innate immune responses induced by H9N2 IAV infection, contributing to its pathogenesis. Full article

Background/Objective: Vaccination is one of the most effective and cost-effective preventive health measures for preventing infectious diseases. The literature reports that children with chronic illnesses have lower vaccination rates than healthy children and are at higher risk for preventable diseases. This study aimed to determine the immunization status of children with chronic illnesses, assess vaccination rates, and help raise awareness on this issue. Material/Method: Children aged 1 month to 18 years who presented to or were admitted to the Pediatric Clinic of Mersin City Education and Research Hospital between 1 March and 30 June 2024, and who were followed up for their chronic illness, and whose parents gave their consent, were included in the study. Sociodemographic data and information about routine and vaccines outside the national immunization schedule (Rotavirus, meningococcal, HPV, Influenza) were obtained from the parents. The status of vaccination of disease-specific recommended vaccines was also recorded. Results: A total of 256 children were included in the study (mean age 8.7 ± 4.69 years; 42.2% girls). A high rate of complete vaccination according to the routine vaccination schedule was observed. However, non-routine vaccinations were administered at low rates: rotavirus 9%, meningococcal 4.7%, and influenza 12.2%. The HPV vaccine was administered to only one patient in the study group. Recommended vaccines for the disease were administered to only 16.4% of eligible children. Conclusions: Children with chronic illnesses are at high risk for infection and complications. Increasing vaccine awareness among both healthcare professionals and parents will contribute to higher immunization rates. Comprehensive studies are needed to identify factors influencing vaccination in this population. Full article

High-pathogenicity avian influenza (HPAI) remains a recurrent threat to poultry production in the Republic of Korea, but production-type-specific clustering has rarely been assessed against the underlying farm population. This retrospective unmatched case–control point-pattern study examined spatial and space–time clustering across six epidemic seasons from 2020 to 2026. We analyzed 486 reported poultry-farm outbreak records together with a national registry of 66,499 poultry farms. The principal analyses compared 204 layer and 204 duck outbreak events with farms of the same production type using the Cuzick–Edwards k-nearest-neighbor statistic, an observed-to-expected clustering-intensity ratio, kernel relative-risk mapping, and spatial and space–time scan statistics. At k = 5, the observed-to-expected intensity ratio was 2.51 for layer events and 1.63 for duck events; this between-type contrast was descriptive because no direct inferential test was performed. Layer-event clustering remained elevated across all seasons, although the extreme 2023–2024 estimate was based on only 15 events. Duck-event clustering was more intermittent and increased in 2025–2026. Premises-level scan statistics identified a broad layer cluster with a relative risk of 3.12 and a smaller duck cluster with a higher local relative risk but far fewer farms. A layer space–time cluster occurred in 2024–2025. These findings support production-type-specific, density-aware surveillance. They do not establish farm-to-farm transmission or implicate egg-handling infrastructure, and they should be interpreted in light of the static registry, repeated-event design, and unmeasured flock size, movements, biosecurity, environmental exposure, and viral lineage. Full article

Airborne transmission represents a primary route of influenza virus dissemination. In animal infection models, conventional intranasal instillation fails to recapitulate the physiological features of natural respiratory infection. Existing aerosol-based challenge methods—including whole-body inhalation and oronasal exposure—face limitations in precise quantification of the delivered infectious dose. Moreover, oronasal exposure systems require specialized, high-cost instrumentation. This study established an economical and dosing-controlled aerosol challenge method utilizing a lung fluid quantitative nebulizer, which can deliver aerosolized virus directly to the lower respiratory tract via endotracheal intubation. The count median aerodynamic diameter (CMAD) of aerosols generated by the nebulizer was 2.28 μm. We compared pulmonary deposition efficiency and pathogenicity between lung-delivery aerosol inhalation and conventional intranasal instillation of PR8 influenza virus in mice. The pulmonary deposition rate for the aerosol inhalation was 63.1%, with an LD₅₀ of 31.1 EID₅₀; in contrast, intranasal instillation achieved a pulmonary deposition rate of 20.0% and an LD₅₀ of 115.0 EID₅₀. Histopathological analysis revealed significantly more severe lesions in lungs of mice challenged via lung-delivery aerosol inhalation relative to those receiving intranasal instillation. Furthermore, using a guinea pig model and a recombinant PR8 virus expressing Gaussia luciferase (PR8-Gluc), we demonstrated that pulmonary aerosol inhalation resulted in both more homogeneous spatial distribution and higher viral loads across lung tissues. Our results demonstrate that animals are more sensitive to lung-delivery inhaled virus than virus delivered by intranasal instillation. This study provides an optimized, economical, and technically straightforward aerosol challenge method with controlled administered dosing for viral infection models. Full article

The completion of this Special Issue, “Coronaviruses and Influenza Viruses: Evolution, Cross-Species Transmission, and Recombination”, offers a valuable opportunity to reflect on the remarkable scientific progress in understanding two of the most critical groups of emerging and re-emerging viral pathogens that affect both human and animal health [...] Full article

This paper proposes a novel susceptible–infected–susceptible (SIS) epidemic model incorporating a fractional-order term and white-noise perturbations. Several analytical results concerning its dynamical behavior are established. Firstly, we prove the existence and uniqueness of model solutions using the Carathéodory approximation. Secondly, the extinction of disease is rigorously proven based on the properties of the quadratic function. Meanwhile, the Ulam–Hyers stability of the model is derived by using stochastic Gronwall-type inequalities and the stochastic analysis techniques. Furthermore, the solution of the proposed fractional-order stochastic model can be approximated by that of the corresponding averaged model under suitable averaging conditions. Then, numerical simulations are conducted to illustrate the effects of key parameters on disease extinction, stability, and long-term dynamical behavior. To improve its adaptability to real-world epidemic dynamics, this paper embeds dynamical constraints into neural networks and constructs a stochastic physics-informed identification framework for seasonal infectious diseases. Empirical results based on monthly influenza data from Xinjiang show that the proposed framework can capture epidemic trends, seasonal peaks, and fitting uncertainty. These results provide a theoretically grounded and practically applicable approach for infectious disease modeling under memory effects and stochastic perturbations. Full article

Background: Despite the increasing availability of tailored vaccines, vaccine-preventable respiratory diseases (VPRDs), including influenza, respiratory syncytial virus (RSV), COVID-19, and pneumococcal disease (PD), continue to impose a significant health and economic burden. This study assessed the epidemiological and economic burden of VPRD among adults aged ≥65 across four Nordic countries (Denmark, Sweden, Norway, and Finland). Methods: Data on incidence, hospital admissions, and mortality were obtained from national statistics (week 21, 2024–week 20, 2025) and supplemented with peer-reviewed literature. A static model was developed to quantify epidemiological and economic burden associated with VPRD during the 2024/2025 winter season. Results: During the 2024/2025 season, VPRD resulted in approximately 830,000 symptomatic cases, 60,300 hospital admissions, and 7750 deaths across the Nordic countries. COVID-19 showed the highest estimated incidence and numbers of hospital admissions, followed by influenza, PD, and RSV. Mortality was comparable between COVID-19 and influenza, followed by PD and RSV. Annual healthcare costs were approximately €1132 million, with productivity losses constituting an additional 7%. Conclusions: Despite national vaccination efforts, VPRDs remain a major health and economic burden in the Nordic countries. Strengthening immunization programs through improved vaccine uptake, broader coverage, and use of advanced vaccines may contribute to further reducing this burden. Full article

Highly pathogenic avian influenza (HPAI) virus H5N1of clade 2.3.4.4b has emerged as the predominant lineage circulating in poultry flocks worldwide, raising concerns regarding the protective efficacy of currently available commercial vaccines, particularly in domestic ducks, which play an important role in virus maintenance and transmission. Thus, this study evaluated the immunogenicity along with the protective efficacy of four inactivated H5 vaccines against a recently isolated local HPAI-H5N1 (Newvalley-3-H5N1-2024, clade 2.3.4.4b) strain in Pekin ducks in Egypt. A total of 150 seronegative ducks were divided into vaccinated and control groups (10 groups) and vaccinated at 10 days of age. At 31 days of age, the vaccinated and positive control groups were challenged using 10^6.5 EID₅₀/0.5 mL/duck with the local isolate (Newvalley-3-H5N1-2024) via the oculo-nasal route. The vaccine efficacy was assessed through clinical signs, survival rate, hemagglutination inhibition (HI) antibody titer, tracheal and cloacal viral shedding quantified by real-time RT-PCR, and histopathological examination of trachea, lung, pancreas, and brain tissues. Generally, all ducks vaccinated with the ValleyVac Avian Flu H5 plus and MEFLUVAC^TM H5 PLUS 8 showed a significantly higher survival rate (100%) at 10 days post-vaccination (DPV) than those in the positive control (66.7% mortality rate). In contrast, ducks exhibited mortality rates ranging from 6.7% in the SERVAC Flu H5N1 group to 13.4% in the Sinder Fluvac group. The ValleyVac Avian Flu H5 plus and MEFLUVAC™ H5 PLUS 8 vaccines induced the highest HI antibody titers at 7, 14, 21, and 28 DPV in both homologous and heterologous AIV antigens, resulting in a significant reduction in viral load among all vaccinated duck groups (p-value < 0.05) comparable to the positive control group. Conversely, the SERVAC Flu H5N1 and Sinder Fluvac vaccines provided partial protection, suboptimal immunogenicity at different time points, and elevated viral shedding. Histopathological findings in ValleyVac Avian Flu H5 plus and MEFLUVAC™ H5 PLUS 8 vaccines exhibited mild tissue alterations following AIV challenge. Marked pathological lesions were observed in the SERVAC Flu H5N1 and Sinder Fluvac vaccinated groups. Among tested vaccines, both ValleyVac Avian Flu H5 plus and MEFLUVAC^TM H5 PLUS 8 showed the highest level of protective efficacy against the circulating AIV strain compared with other commercial vaccines. This study highlights the need for continuous molecular surveillance, antigenic matching, and regular updating of vaccine seed strains to ensure efficient HPAI control in Egypt. Full article

Background/Objectives: Obesity is associated with respiratory infection risk, but its relationship with post-discharge healthcare burden remains unclear. This study examined the associations of body mass index (BMI) and waist circumference (WC), evaluated separately, with hospitalization and post-discharge outcomes in analyses stratified by sex among South Korean adults with claims-defined hospitalizations involving influenza or pneumonia. Methods: This retrospective cohort study used the 2018 National Health Insurance Service (NHIS) Customized Research Database linked to health-screening data. Adults aged 20–89 years with claims-defined hospitalizations involving influenza or pneumonia were included if BMI and WC measurements were available from the most recent NHIS health-screening examination conducted within two years before the index admission. Length of stay and index hospitalization costs were summarized descriptively. Cox proportional hazards models were used to estimate hazard ratios (HRs) for all-cause and pneumonia-related readmission within two years after discharge, and two-part models were used to estimate readmission-related costs, expressed in US dollars (USD). Results: The cohort included 175,774 patients, of whom 80,257 (45.7%) were male. Category-specific associations varied according to the anthropometric measure, outcome, and sex stratum. In female patients, the highest WC category had the largest estimated all-cause readmission HR (HR 1.195, 95% confidence interval 1.157–1.235), and the highest model-based mean cost of the first all-cause readmission was also observed in this category (USD 1407.4). In male patients, several higher BMI categories had lower estimated readmission HRs than the reference category; however, these estimates should not be interpreted as protective effects because competing mortality was not accounted for using competing-risk methods. Patterns for pneumonia-related readmission and costs were less consistent. Conclusions: BMI and WC showed category-specific associations with readmission, while model-based mean readmission costs varied across anthropometric categories and sex strata. Higher WC categories were associated with higher all-cause readmission HRs in the female stratum; however, the independent or incremental prognostic value of BMI and WC was not evaluated. Full article

Background: Conformational stability has been shown to modulate the immunogenicity of structural class 1 viral fusion glycoproteins, yet the relationship between influenza A hemagglutinin (HA) stability and antigenicity remains poorly understood. Methods: Here, we screened a panel of 21 A/Hawaii/70/2019 (H1N1) HA mutants for expression, cleavage, and acid and conformational stability in cells. Twelve mutant HA proteins expressed from transfected plasmid constructs that showed relatively robust expression compared to WT also exhibited either altered stability or glycosylation deletion. mRNA-LNPs were generated containing these 12 HAs, along with the wild-type (WT) HA, to investigate the mutational effects on mRNA-LNP vaccine immunogenicity and protection in mice. Hemagglutination inhibition, microneutralization, and total serum IgG ELISAs were performed using a panel of H1N1 antigens to evaluate humoral immune responses at 28 days post vaccination. The vaccinated mice were then subjected to lethal challenge with a forward-drifted H1N1 virus. Results: Most mutant HA candidates elicited WT-like serological responses and provided protection against challenge, although noticeable decreases in serological responses and, to a lesser extent, protection were observed, especially among G72K- and R109E-vaccinated mice. Of note, substitutions at position E107 enhanced total IgG responses against the HA stalk. Modest, but detectable, increases in antibody-dependent cellular cytotoxicity (ADCC) were also observed, particularly with E107R. Although substitution-specific differences in weight loss were found in E107-vaccinated mice challenged with a mouse-adapted Cal/09 virus, these differences were minor, and protection against the forward-drifted challenge virus and a heterologous PR8 challenge virus was no different from that in mice vaccinated with WT HA. Conclusions: These findings demonstrate the ability of specific substitutions to alter components of humoral immunity by shifting HA domain-specific antibody responses, which could prove useful in the design and development of HA vaccine antigens possessing optimized immunogenicity. Full article

Background: Trimeric envelope-proximal domains in viral class I fusion proteins are conserved targets of broadly neutralizing antibodies (bNAbs), but it has proven difficult to develop vaccines against those targets. The HIV-1 gp41 membrane-proximal external region (MPER) is one such target. Induction of a neutralizing response likely depends on the immunogen having a close-to-native structure. Methods: Native sequence MPER was displayed on genome-reduced bacteria as a coiled-coil homotrimer using a Haemophilus influenzae Hia trimeric autotransporter. Vaccine designs incorporated additional features, including trimerization domains to stabilize MPER, tandem MPER repeats to increase antigen valency, and immunomodulatory elements. Antigen exposure was assessed by flow cytometry, antibody responses were evaluated by ELISA, and functional activity was measured using HIV-1 pseudovirus neutralization assays. Results: Trimer stabilization improved MPER exposure, but immunogen visibility alone did not predict neutralization. After three immunizations, neutralizing activity was detected only in the most extensively engineered vaccine, which neutralized tier 2 virus CNE55. After five immunizations, the same vaccine also neutralized the tier 2 virus 25710-2.43. A further design modification that included an extended Hia-derived spacer increased MPER exposure and antibody binding, with neutralization detected against MN.3, X1632_S2_B10, and 25710-2.43 viruses in subsets of animals. Conclusions: As a proof-of-concept, native-sequence MPER can induce detectable, though modest and virus-dependent, HIV-1 neutralizing activity when displayed in a carefully controlled trimeric bacterial surface-display platform. The results show that MPER vaccine performance depends not only on antigen exposure, but also on multimeric organization, immunomodulatory context, and antigen-scaffold geometry. Analogous coiled-coil trimeric bacterial surface display immunogens may inform vaccine development for stem/stalk regions of other Class I fusion protein viruses. Full article

Background: Influenza is primarily a respiratory illness, but it is increasingly linked to acute cardiovascular complications, including myocarditis and sudden cardiac death. Evidence on influenza-associated cardiac involvement remains fragmented and largely derived from case-based reports. Methods: This systematic review followed PRISMA guidelines and was registered with PROSPERO (CRD420251249130). PubMed, Web of Science, and Google Scholar were searched for eligible studies. Case reports and case series were included to characterize rare, severe, or atypical cardiac manifestations that are not captured in larger epidemiological studies. Data on demographics, influenza subtype, cardiac manifestations, investigations, management, and outcomes were extracted. Results: Thirty-three studies (32 case reports and one case series) comprising 36 cases were included. Influenza A was reported in 26 cases and influenza B was reported in 9 cases. Myocarditis was the most common manifestation (19 cases, 53%), including fulminant myocarditis in 9 cases (25%). Cardiogenic shock occurred in seven cases (19%), malignant arrhythmias in four(11%), myocardial infarction–like presentations in three (8%), and cardiac arrest or sudden cardiac death in six cases (17%). Cardiac involvement occurred across all age groups, frequently in patients without pre-existing coronary artery disease. Overall mortality was 44% (16/36), with fatalities reported in both influenza A and B infections. These findings predominantly reflect severe and published cases and may not represent the full clinical spectrum of influenza-associated cardiac involvement. Conclusions: This review highlights that influenza infection has been reported in association with a range of acute cardiac manifestations, particularly myocarditis, including severe and fulminant presentations. However, given the reliance on case reports and case series, the findings are subject to significant publication bias and do not permit the estimation of incidence, risk, or causal inference. These observations should therefore be interpreted as hypothesis-generating. Full article

Although most upper respiratory tract infections (URTIs) have a viral etiology, antibiotics are widely prescribed, thus contributing substantially to antimicrobial resistance. This study investigated the potential beneficial effects of a novel strain, Limosilactobacillus reuteri LMG P-27481, against major URT pathobionts (Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Moraxella catarrhalis, and Haemophilus influenzae) with the aim of reducing or delaying antibiotic use. Antibacterial and immunomodulatory activities were evaluated using L. reuteri alone or combined with resveratrol, a natural compound with antiviral and anti-inflammatory properties. Both agents inhibited pathogen growth, while their combination showed additive antibacterial activity, particularly against Gram-negative bacteria. Antioxidant assays demonstrated significant antioxidant capacity for both agents, with enhanced effects in combination in NBT and ABTS assays but antagonistic in ORAC. Immune mediators (IL-6, IL-8, IL-1β, TNF-α, IL-25, IL-33, CCL17, CCL22) were assessed in epidermal, epithelial, and macrophage cell lines, together with epidermal integrity markers (Filaggrin, Loricrin, Involucrin) in a 3D reconstructed human skin model (EpiDermFT^TM). L. reuteri, resveratrol, and their combination exerted cell-specific effects in the different models, modulating cytokine expression and production, and barrier integrity. Our findings support the potential efficacy of oral L. reuteri LMG P-27481 plus resveratrol in URTIs. Full article

Background/objectives: The emergence of highly pathogenic avian influenza A (H5N1) virus infections in dairy cattle in the United States revealed a novel mammalian host and a potential transmission pathway involving raw milk and dairy production systems. Sustained circulation of H5N1 in dairy herds is of concern because ongoing viral adaptation in mammals may increase the risk of efficient mammalian transmission and subsequent zoonotic spread. In response to this emerging threat, we developed a chimpanzee adenovirus (ChAd)-vectored vaccine expressing the haemagglutinin 5 antigen (H5HA) from the dairy cattle isolate A/dairy cattle/Texas. Methods: Lactating dairy cows were vaccinated by either intramuscular (N = 3) or intranasal administration (N = 3). H5HA clade 2.3.4.4b antibodies in cow’s milk and sera were evaluated by ELISA. Hemagglutination and neutralisation capacity were also evaluated. Results: IgG and IgA H5HA-specific antibodies were detected in serum and milk from parenterally vaccinated animals, demonstrating the induction of a systemic immune response. The neutralising antibody responses elicited were only detected in serum of cows vaccinated via the intramuscular route. Conclusions: These preliminary findings support the feasibility of ChAd-vectored vaccination as a strategy to induce humoral immunity in cattle against emerging H5N1 influenza A viruses. Cross-reactive antibody responses against both A/dairy cattle/Texas/24-008749_001/2024 and A/Ibis/Egypt/RLQP-229S/2022 support the capacity of the vaccine to recognise antigenically related H5N1 clade 2.3.4.4b viruses circulating in mammalian and avian reservoirs. Further studies of vaccine efficacy and the immunological mechanism of protection should now be undertaken with the aim of reducing viral transmission and milk-associated shedding in dairy herds. Full article

The emergence of highly pathogenic avian influenza viruses (AIVs) poses significant threats to global public health and the poultry economy. Rapid detection methods targeting the hemagglutinin (HA) protein have become increasingly unreliable due to ongoing antigenic drift and genetic mutations. In this study, we screened two monoclonal antibodies (mAbs) against the highly conserved neuraminidase (NA) protein, which were characterized by high affinity and specificity for the N9 subtype. Using the paired mAbs 12A2 and 12F12, an NA-targeting lateral flow immunoassay (NA-LFIA) was developed for the rapid detection of N9 subtype AIVs. The NA-LFIA demonstrated exceptional specificity, exhibiting no cross-reactivity with the N1, N2, or N6 subtypes. The limits of detection (LODs) were established at 10^3.3 TCID₅₀/0.1 mL for the virus and 98 ng/mL for the recombinant NA protein. The test strips exhibited excellent reproductivity for detecting the NA antigen, with intra-assay and inter-assay variations of 5.32% and 6.05%, respectively. Stability testing confirmed a six-month shelf life without any loss of sensitivity. These finds indicate that the NA-LFIA is a robust, rapid point-of-care testing (POCT) tool for the early detection of N9 subtype AIV infection. Full article