Respiratory syncytial virus: from pathogenesis to potential therapeutic strategies

The Epidemiology of Respiratory Syncytial Virus: New Trends and Future Perspectives

RSV (respiratory syncytial virus) is a major cause of acute lower respiratory tract infection (LRTI) worldwide [...].

Farnesyltransferase inhibitor lonafarnib suppresses respiratory syncytial virus infection by blocking conformational change of fusion glycoprotein

Respiratory syncytial virus (RSV) is the major cause of bronchiolitis and pneumonia in young children and the elderly. There are currently no approved RSV-specific therapeutic small molecules available. Using high-throughput antiviral screening, we identified an oral drug, the prenylation inhibitor lonafarnib, which showed potent inhibition of the RSV fusion process. Lonafarnib exhibited antiviral activity against both the RSV A and B genotypes and showed low cytotoxicity in HEp-2 and human primary bronchial epithelial cells (HBEC). Time-of-addition and pseudovirus assays demonstrated that lonafarnib inhibits RSV entry, but has farnesyltransferase-independent antiviral efficacy. Cryo-electron microscopy revealed that lonafarnib binds to a triple-symmetric pocket within the central cavity of the RSV F metastable pre-fusion conformation. Mutants at the RSV F sites interacting with lonafarnib showed resistance to lonafarnib but remained fully sensitive to the neutralizing monoclonal antibody palivizumab. Furthermore, lonafarnib dose-dependently reduced the replication of RSV in BALB/c mice. Collectively, lonafarnib could be a potential fusion inhibitor for RSV infection.

Xuanfei Formula inhibited RSV infection by normalizing the SREBP2-mediated cholesterol synthesis process

Background and aims

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infections in children and the elderly, often progressing to pneumonia and severe sequelae. However, there are currently no feasible and cost-effective interventions with proven efficacy for children, making medications with anti-RSV activity urgently needed. Traditional Chinese medicine has shown promising therapeutic efficacy in alleviating viral infection symptoms. Therefore, we aimed to develop effective strategies for RSV treatment based on traditional Chinese medicine.

Methods and results

The infection status was assessed in BALB/c mice with or without Xuanfei Formula (XFF) treatment over a one-week period using H&E staining, cytokine assays and RSV titer testing after RSV challenge. Remarkably, on the first day of XFF intervention, both the pro-inflammation cytokine levels in the serum and RSV-N gene copies in the lung of mice were plummeted, compared to the RSV-infected group. This implied that XFF might possess the immune-independent anti-RSV capability. To elucidate the underlying mechanism, we employed transcriptome analysis followed by k-means analysis. The reversal effects of XFF against RSV primarily focused on the processes of innate and adaptive immunity. Additionally, we found that XFF administration corrected the disordered fatty acid and cholesterol metabolism processes during RSV infection. Lipidomics profiling indicated consistent cholesterol abundance with transcriptional changes but not fatty acids. Cholesterol synthesis-related genes mRNA levels and cholesterol synthesis intermediates detection supported XFF's repression upon cholesterol biosynthesis. Aberrantly increased cholesterol production has been reported as necessary for RSV infection. To mimic that, we observed lovastatin treatment inhibited RSV replication and pro-inflammation cytokine expression in vitro. Transcription factor prediction of differentially expressed genes (DEGs) involved in cholesterol synthesis implicated SREBP2. Through network pharmacology, stigmasterol and β-sitosterol were identified as the effective active ingredients within the XFF, with the help of further molecular docking and mass spectrum detection. In vitro experiments demonstrated β-sitosterol and stigmasterol reinforced the bonding between SREBP cleavage-activation protein (SCAP) and insulin-induced gene proteins (INSIGs) to inhibit SREBP2 cleavage maturation and consequent RSV infection.

Conclusion

Xuanfei Formula (XFF) exhibits excellent anti-RSV efficacy by inhibiting SREBP2-mediated cholesterol synthesis to reduce RSV replication and ameliorate inflammation in the lung of infected mice.

Birth characteristics as predictors of respiratory syncytial virus hospitalisation in newborns to optimise immunisation schedule

AIM

To examine birth characteristics that influence infant respiratory syncytial virus (RSV) hospitalisation risk in order to identify risk factors for severe RSV infections.

METHODS

Retrospective cohort study of 460 771 Sicilian children under 6 months old from January 2007 to December 2017. Hospital discharge records were consulted to identify cases and hospitalisations with International Classification of Diseases, Ninth Revision, Clinical Modification codes 466.11 (RSV bronchiolitis), 480.1 (RSV pneumonia) and 079.6 (RSV). RSV hospitalisation risk was estimated using adjusted odds ratios (aOR) and 95% confidence intervals (95% CI).

RESULTS

Overall, 2420 (5.25 per 1000 infants) RSV-related hospitalisations were identified during the study, with girls accounting for 52.8%. RSV hospitalisation risk increased for full-term, transferred, extreme immature, and preterm neonates with serious issues (aOR 3.25, 95% CI 2.90-3.64; aOR 1.86, 95% CI 1.47-2.32; aOR 1.54, 95% CI 1.11-2.07; and aOR 1.48, 95% CI 1.14-1.90). Compared to children born in June, the risk of RSV hospitalisation was significantly higher in children born in January (aOR 28.09, 95% CI 17.68-48.24) and December (aOR 27.36, 95% CI 17.21-46.99).

CONCLUSION

This study identified birth month and diagnosis-related groups as key predictors of RSV hospitalisations. This could help manage monoclonal antibody appropriateness criteria.

Regulatory role of miRNAs in the human immune and inflammatory response during the infection of SARS-CoV-2 and other respiratory viruses: A comprehensive review

miRNAs are single-stranded ncRNAs that act as regulators of different human body processes. Several miRNAs have been noted to control the human immune and inflammatory response during severe acute respiratory infection syndrome (SARS-CoV-2) infection. Similarly, many miRNAs were upregulated and downregulated during different respiratory virus infections. Here, an attempt has been made to capture the regulatory role of miRNAs in the human immune and inflammatory response during the infection of SARS-CoV-2 and other respiratory viruses. Firstly, the role of miRNAs has been depicted in the human immune and inflammatory response during the infection of SARS-CoV-2. In this direction, several significant points have been discussed about SARS-CoV-2 infection, such as the role of miRNAs in human innate immune response; miRNAs and its regulation of granulocytes; the role of miRNAs in macrophage activation and polarisation; miRNAs and neutrophil extracellular trap formation; miRNA-related inflammatory response; and miRNAs association in adaptive immunity. Secondly, the miRNAs landscape has been depicted during human respiratory virus infections such as human coronavirus, respiratory syncytial virus, influenza virus, rhinovirus, and human metapneumovirus. The article will provide more understanding of the miRNA-controlled mechanism of the immune and inflammatory response during COVID-19, which will help more therapeutics discoveries to fight against the future pandemic.

Prevention and Potential Treatment Strategies for Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is a significant viral pathogen that causes respiratory infections in infants, the elderly, and immunocompromised individuals. RSV-related illnesses impose a substantial economic burden worldwide annually. The molecular structure, function, and in vivo interaction mechanisms of RSV have received more comprehensive attention in recent times, and significant progress has been made in developing inhibitors targeting various stages of the RSV replication cycle. These include fusion inhibitors, RSV polymerase inhibitors, and nucleoprotein inhibitors, as well as FDA-approved RSV prophylactic drugs palivizumab and nirsevimab. The research community is hopeful that these developments might provide easier access to knowledge and might spark new ideas for research programs.

Regulation and functions of the NLRP3 inflammasome in RNA virus infection

Virus infection is one of the greatest threats to human life and health. In response to viral infection, the host's innate immune system triggers an antiviral immune response mostly mediated by inflammatory processes. Among the many pathways involved, the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome has received wide attention in the context of viral infection. The NLRP3 inflammasome is an intracellular sensor composed of three components, including the innate immune receptor NLRP3, adaptor apoptosis-associated speck-like protein containing CARD (ASC), and the cysteine protease caspase-1. After being assembled, the NLRP3 inflammasome can trigger caspase-1 to induce gasdermin D (GSDMD)-dependent pyroptosis, promoting the maturation and secretion of proinflammatory cytokines such as interleukin-1 (IL-1β) and interleukin-18 (IL-18). Recent studies have revealed that a variety of viruses activate or inhibit the NLRP3 inflammasome via viral particles, proteins, and nucleic acids. In this review, we present a variety of regulatory mechanisms and functions of the NLRP3 inflammasome upon RNA viral infection and demonstrate multiple therapeutic strategies that target the NLRP3 inflammasome for anti-inflammatory effects in viral infection.

Qingfei Formula Protects against Human Respiratory Syn cytial Virus-induced Lung Inflammatory Injury by Regulating the M APK Signaling Pathway

OBJECTIVE

Qingfei formula (QF) is an empirical formula that shows good clinical efficacy in treating human respiratory syncytial virus pneumonia (RSVP). However, the underlying mechanism remains unclear. This study explores the possible pharmacological actions of QF in RSVP treatment.

METHODS

We used a network pharmacology approach to identify the active ingredients of QF, forecast possible therapeutic targets, and analyze biological processes and pathways. Molecular docking simulation was used to evaluate the binding capability of active ingredients and therapeutic targets. Finally, in vivo experiments confirmed the reliability of network pharmacology-based prediction of underlying mechanisms.

RESULTS

The study identified 92 potential therapeutic targets and corresponding 131 active ingredients. Enrichment analysis showed that QF downregulated the MAPK signaling pathway and suppressed the inflammatory injury to the lungs induced by the RSV virus. Molecular docking simulations demonstrated that the core active ingredients of QF could stably bind to genes associated with the MAPK signaling pathway. QF had a protective effect against pneumonia in RSV-infected mice. The QF group exhibited a significant reduction in the levels of inflammatory mediators, interleukin- 6 (IL-6), interleukin-8 (CXCL8, IL-8), and P-STAT3, compared to the RSV-induced group. The QF group showed remarkably inhibited MAPK1+3(P-ERK1+2) and MAPK8(P-JNK) protein expression.

CONCLUSION

The current study showed that QF downregulated the MAPK signaling pathway, which inhibited pulmonary inflammation triggered by RSV infection. This study recommends the appropriate use of QF in the clinical management of RSVP.

Arexvy: A Comprehensive Review of the Respiratory Syncytial Virus Vaccine for Revolutionary Protection

The respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract infection in children and poses a significant risk to older adults. Developing a vaccine against RSV has been a priority, and the recently approved Arexvy vaccine has shown promise in preventing lower respiratory tract disease (LRTD) caused by RSV in individuals aged 60 years and older. This comprehensive review discusses the history of RSV, challenges in vaccine development, and the mechanism of action of Arexvy. The efficacy and safety of the vaccine are explored based on phase 3 clinical trial, demonstrating its effectiveness in preventing RSV-associated LRTD. The most common adverse reactions reported include injection site pain, fatigue, myalgia, headache, and arthralgia. Ongoing research focuses on the long-term effectiveness of Arexvy, including the need for booster doses and its impact on reducing RSV-associated hospitalizations. The potential of Arexvy to lessen the burden of RSV-related illnesses, particularly in vulnerable populations, is highlighted, emphasizing the importance of widespread immunization efforts and accessibility to this groundbreaking vaccine.

Epidemiological characteristics of respiratory syncytial virus infection in pediatric patients before, during the COVID-19 pandemic and after easing of COVID-19 restrictive measures in China

We aimed to assess the epidemiological characteristics of respiratory syncytial virus (RSV) infection in Chinese children at different phases of the coronavirus disease 2019 (COVID-19) pandemic, that is, before, during the pandemic and after easing of restrictive measures. We included 123 623 patients aged 0-18 years with respiratory infection symptoms who were suspected with RSV infection from January 1, 2019 to June 30, 2023 in Hangzhou Children's Hospital. Clinical information and RSV test result were extracted from the laboratory information system. We calculated the positive rate of RSV detection by age groups, gender, seasons, types of patients and phases of COVID-19 pandemic. Nonlinear associations between age and risk of RSV infection in three phases of pandemic were assessed by restricted cubic spline regression models. Among 123 623 patients, 3875 (3.13%) were tested as positive. The highest positive rate was observed in children aged 0-28 days (i.e., 12.28%). RSV infection was most prevalent in winter (6.04%), and followed by autumn (2.52%). Although there is no statistical significance regarding the positive rate at three phases of the pandemic, we observed that the rate was lowest during the pandemic and increased after easing the measures in certain age groups (p < 0.05), which was consisted with results from the nonlinear regression analyses. In addition, regression analyses suggested that the age range of children susceptible to RSV got wider, that is, 0-3.5 years, after easing all restrictive measures compared with that before (i.e., 0-3 years) and during the pandemic (i.e., 0-1 year). Based on our findings, we called for attention from health professionals and caregivers on the new epidemiological characteristics of RSV infection in the post-pandemic era after easing the restrictive measures.

Multicenter evaluation of the Acaruiter Respiratory Panel for diagnosis of respiratory tract infections in Chinese children

IMPORTANCE

Compared to multiplex PCR assays that are available in the Chinese market, the Acaruiter Respiratory Panel (fluorescent PCR) covers a wider range of pathogens including eight viruses, five bacteria, Mycoplasma pneumoniae and Chlamydia pneumoniae, and has high accuracy and effectiveness in the detection of pathogens. This is the first study to evaluate the performance of the Acaruiter Respiratory Panel. This regent may be a promising assay for comprehensive testing for respiratory pathogens from nasopharyngeal swab specimens in Chinese children.

Global burden and trends of respiratory syncytial virus infection across different age groups from 1990 to 2019: A systematic analysis of the Global Burden of Disease 2019 Study

OBJECTIVE

Understanding the global patterns of respiratory syncytial virus (RSV) is crucial for developing effective prevention and control strategies.

METHODS

Data on RSV-related burden were extracted from the Global Burden of Disease 2019. Joinpoint regression models were used to assess the global temporal trends of RSV and further stratified analyses were conducted according to the Socio-demographic Index (SDI), which is a composite measure of income, education, and total fertility. Age-period-cohort model was used to evaluate age, period, and cohort effects.

RESULTS

In 2019, the global age-standardized rate of mortality (ASMR) and disability-adjusted life years (ASR-DALYs) of RSV were 4.79/100,000 (95% uncertainty interval [95% UI]: 1.82/100,000-9.32/100,000) and 218.34/100,000 (95% UI: 92.06/100,000-376.80/100,000), respectively. The burden of RSV was higher in men than women. The highest ASMR (10.26/100,000, 3.80/100,000-20.16/100,000) and ASR-DALYs (478.71/100,000, 202.40/100,000-840.85/100,000) were reported in low-SDI region. Although mortality and DALYs rates in all age groups declined globally, the pace of decline was not uniform across age groups. Mortality rate in the elderly over 70 years surpassed that in children under 5 years in 2019.

CONCLUSION

This study highlights the need for targeted interventions to reduce the burden of RSV, particularly in low-SDI region, and among the elderly over 70 years.

The Estimate of Parental Quality of Life Loss Due to Respiratory Syncytial Virus (RSV) Hospitalization

BACKGROUND

Respiratory syncytial virus (RSV) is one of the leading causes of pediatric hospitalizations, mainly in children under 2 years of age. Hospitalization affects the caregivers' quality of life (QoL). We assessed the caregivers' QoL during RSV-confirmed hospitalizations of children under 2 years old, identified the most affected QoL dimensions and calculated utilities focusing on the assessment methods and potential confounders.

METHODS

The caregivers filled out the EQ-5D questionnaire, consisting of a descriptive system (assessing 5 QoL dimensions) and a visual analog scale (EQ VAS). Utility, utility loss and quality-adjusted life years (QALY) loss were calculated, and a concordance between the two systems was assessed.

RESULTS

A disturbance in any of the five assessed dimensions was reported by 42% (55 out of 132) of the caregivers, mostly anxiety/depression (37%) and pain/discomfort (17%). The utilities varied between 0.17 and 1 in the descriptive system and 0.33-1 (median 0.86) in the EQ VAS, with a utility loss of 0.14 (IQR: 0.1-0.2). The calculated QALY loss reached a median of 2.45 × 10-3 (IQR: 1.37 × 10-3-4.56 × 10-3) and was not influenced by the patient's age or the final clinical diagnosis (QALY loss for bronchiolitis: 2.74 × 10-3, pneumonia: 1.84 × 10-3, bronchitis: 1.78 × 10-3, differences statistically insignificant). Only a moderate concordance between the descriptive system and the EQ VAS was seen (Spearman's rank correlation coefficient = 0.437, p < 0.05), with the latter revealing a higher degree of QoL disturbances.

CONCLUSIONS

RSV hospitalization influences parental QoL significantly, and anxiety/depression is the most commonly reported issue. Utility impairment scores depend on the assessment method but not on the patient's age or final diagnosis. Thus, the impact of RSV on caregivers' QoL cannot be underestimated.

Case Report: ASCENIV use in three young children with immune abnormalities and acute respiratory failure secondary to RSV infection

Respiratory syncytial virus (RSV) is the most common etiology of bronchiolitis in young children. While most children clinically improve with care at home, RSV is the leading cause of hospitalization among infants aged 12 months or less. Common modalities of treatment for children with immune dysregulation include respiratory support and best supportive care, which may include immunoglobulin therapy. All immunoglobulin therapies adhere to Food and Drug Administration (FDA) - established standards for antibodies against measles, polio, and diphtheria, but there are no required standards for problematic respiratory viral pathogens, including RSV and others. ASCENIV is an approved IVIG that is manufactured from blending normal source plasma with plasma from donors that possess high antibody titers against RSV and other respiratory pathogens of concern. ASCENIV was developed, in part, to the unmet need that exists in immunocompromised patients who lack sufficient antibodies against problematic viral pathogens. ASCENIV is not a currently approved treatment for severe RSV and other viral infections. There is a lack of research regarding its potential benefits in the acute treatment period for RSV and in the pediatric population. Therefore, this case series was developed to describe real-world experiences of ASCENIV use in this less well studied clinical scenario. This case series reviews three pediatric patients ≤ 5 years of age with immune dysregulation and who were severely ill with RSV. Despite receiving best supportive care, and standard immunoglobulin therapy for some, the patients' clinical status continued to decline. All patients received ASCENIV in an intensive care setting. Each patient had ultimately recovered due to the various medical interventions done. This case series demonstrated that ASCENIV (500mg/kg) administration may have contributed to the treatment outcomes of a less well studied age-cohort of patients. In addition, no adverse side effects were observed after ASCENIV administration. Further analysis of the benefits of ASCENIV for the acute and preventative treatment in patients younger than 12 years of age with immune dysregulation should continue to be explored.

Respiratory syncytial virus entry mechanism in host cells: A general overview

Respiratory syncytial virus (RSV) is a virus that causes acute respiratory infections in neonates and older adults. To infect host cells, the attachment glycoprotein (G) interacts with a cell surface receptor. This interaction determines the specific cell types that are susceptible to infection. RSV possesses a type I fusion protein F. Type I fusion proteins are metastable when rearrangement of the prefusion F occurs; the fusion peptide is exposed transforming the protein into postfusion form. The transition between the prefusion form and its postfusion form facilitates the viral envelope and the host cell membrane to fuse, enabling the virus to enter the host cell. Understanding the entry mechanism employed by RSV is crucial for developing effective antiviral therapies. In this review, we will discuss the various types of viral fusion proteins and explore the potential entry mechanisms utilized by RSV. A deeper understanding of these mechanisms will provide valuable insights for the development of novel approaches to treat RSV infections.

Interferons as negative regulators of ILC2s in allergic lung inflammation and respiratory viral infections

Group 2 innate lymphoid cells (ILC2s), characterized by a lack of antigen receptors, have been regarded as an important component of type 2 pulmonary immunity. Analogous to Th2 cells, ILC2s are capable of releasing type 2 cytokines and amphiregulin, thus playing an essential role in a variety of diseases, such as allergic diseases and virus-induced respiratory diseases. Interferons (IFNs), an important family of cytokines with potent antiviral effects, can be triggered by microbial products, microbial exposure, and pathogen infections. Interestingly, the past few years have witnessed encouraging progress in revealing the important role of IFNs and IFN-producing cells in modulating ILC2 responses in allergic lung inflammation and respiratory viral infections. This review underscores recent progress in understanding the role of IFNs and IFN-producing cells in shaping ILC2 responses and discusses disease phenotypes, mechanisms, and therapeutic targets in the context of allergic lung inflammation and infections with viruses, including influenza virus, rhinovirus (RV), respiratory syncytial virus (RSV), and severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2).

Integrating metabolomics and network pharmacology to assess the effects of quercetin on lung inflammatory injury induced by human respiratory syncytial virus

Quercetin (QR) has significant anti-respiratory syncytial virus (RSV) effects. However, its therapeutic mechanism has not been thoroughly explored. In this study, a lung inflammatory injury model caused by RSV was established in mice. Untargeted lung tissue metabolomics was used to identify differential metabolites and metabolic pathways. Network pharmacology was used to predict potential therapeutic targets of QR and analyze biological functions and pathways modulated by QR. By overlapping the results of the metabolomics and the network pharmacology analyses, the common targets of QR that were likely to be involved in the amelioration of RSV-induced lung inflammatory injury by QR were identified. Metabolomics analysis identified 52 differential metabolites and 244 corresponding targets, while network pharmacology analysis identified 126 potential targets of QR. By intersecting these 244 targets with the 126 targets, hypoxanthine-guanine phosphoribosyltransferase (HPRT1), thymidine phosphorylase (TYMP), lactoperoxidase (LPO), myeloperoxidase (MPO), and cytochrome P450 19A1 (CYP19A1) were identified as the common targets. The key targets, HPRT1, TYMP, LPO, and MPO, were components of purine metabolic pathways. The present study demonstrated that QR effectively ameliorated RSV-induced lung inflammatory injury in the established mouse model. Combining metabolomics and network pharmacology showed that the anti-RSV effect of QR was closely associated with purine metabolism pathways.

Pathologic Mechanisms of the Newcastle Disease Virus

Newcastle disease (ND) has been a consistent risk factor to the poultry industry worldwide. Its pathogen, Newcastle disease virus (NDV), is also a promising antitumor treatment candidate. The pathogenic mechanism has intrigued the great curiosity of researchers, and advances in the last two decades have been summarized in this paper. The NDV’s pathogenic ability is highly related to the basic protein structure of the virus, which is described in the Introduction of this review. The overall clinical signs and recent findings pertaining to NDV-related lymph tissue damage are then described. Given the involvement of cytokines in the overall virulence of NDV, cytokines, particularly IL6 and IFN expressed during infection, are reviewed. On the other hand, the host also has its way of antagonizing the virus, which starts with the detection of the pathogen. Thus, advances in NDV’s physiological cell mechanism and the subsequent IFN response, autophagy, and apoptosis are summarized to provide a whole picture of the NDV infection process.

Andrographolide exerts anti-respiratory syncytial virus activity by up-regulating heme oxygenase-1 independent of interferon responses in human airway epithelial cells

BACKGROUND

Respiratory syncytial virus (RSV) is the leading cause of mortality and morbidity in children under the age of five. Despite this, there is still a lack of safe and effective vaccines and antiviral agents for clinical use. Andrographolide exerts antiviral functions against a variety of viruses, but whether (and how) it exerts antiviral effects on RSV remains unclear.

METHODS AND RESULTS

In vitro RSV infection models using A549 and 16HBE cell lines were established, and the effects of andrographolide on RSV were analyzed via RSV N gene load and proinflammatory cytokine levels. The RNA transcriptome was sequenced, and data were analyzed by R software. Andrographolide-related target genes were extracted via network pharmacology using online databases. Lentiviral transfection was applied to knockdown the heme oxygenase-1 gene (Hmox1, HO-1). Results showed that andrographolide suppressed RSV replication and attenuated subsequent inflammation. Network pharmacology and RNA sequencing analysis indicated that the hub gene HO-1 may play a pivotal role in the anti-RSV effects of andrographolide. Furthermore, andrographolide exerted antiviral effects against RSV partially by inducing HO-1 but did not activate the antiviral interferon response.

CONCLUSION

Our findings demonstrated that andrographolide exerted anti-RSV activity by up-regulating HO-1 expression in human airway epithelial cells, providing novel insights into potential therapeutic targets and drug repurposing in RSV infection.

Responding to Higher-Than-Expected Infant Mortality Rates from Respiratory Syncytial Virus (RSV): Improving Treatment and Reporting Strategies

Respiratory syncytial virus (RSV) has a major role in respiratory infections in young infants around the world. However, substantial progress has been made in recent years in the field of RSV. A wide variety of observational studies and clinical trials published in the past decade provide a thorough idea of the health and economic burden of RSV disease in the developing world. In this review, we discuss the impact of RSV burden of disease, major gaps in disease estimations, and challenges in generating new therapeutic options and an immune response against the virus, and briefly describe next generation technologies that are being evaluated.

Biochemistry of the Respiratory Syncytial Virus L Protein Embedding RNA Polymerase and Capping Activities

The human respiratory syncytial virus (RSV) is a negative-sense, single-stranded RNA virus. It is the major cause of severe acute lower respiratory tract infection in infants, the elderly population, and immunocompromised individuals. There is still no approved vaccine or antiviral treatment against RSV disease, but new monoclonal prophylactic antibodies are yet to be commercialized, and clinical trials are in progress. Hence, urgent efforts are needed to develop efficient therapeutic treatments. RSV RNA synthesis comprises viral transcription and replication that are catalyzed by the large protein (L) in coordination with the phosphoprotein polymerase cofactor (P), the nucleoprotein (N), and the M2-1 transcription factor. The replication/transcription is orchestrated by the L protein, which contains three conserved enzymatic domains: the RNA-dependent RNA polymerase (RdRp), the polyribonucleotidyl transferase (PRNTase or capping), and the methyltransferase (MTase) domain. These activities are essential for the RSV replicative cycle and are thus considered as attractive targets for the development of therapeutic agents. In this review, we summarize recent findings about RSV L domains structure that highlight how the enzymatic activities of RSV L domains are interconnected, discuss the most relevant and recent antivirals developments that target the replication/transcription complex, and conclude with a perspective on identified knowledge gaps that enable new research directions.

Alkaloids as potential antivirals. A comprehensive review

Alkaloids are a diverse group of natural phytochemicals. These phytochemicals in plants provide them protection against pests, and herbivorous organisms and also control their development. Numerous of these alkaloids have a variety of biological effects, and some have even been developed into medications with different medicinal properties. This review aims to provide a broad overview of the numerous naturally occurring alkaloids (isolated from both terrestrial and aquatic species) along with synthetically produced alkaloid compounds having prominent antiviral properties. Previous reviews on this subject have focused on the biological actions of both natural and synthetic alkaloids, but they have not gone into comprehensive detail about their antiviral properties. We reviewed here several antiviral alkaloids that have been described in the literature in different investigational environments i.e. (in-vivo, in-ovo, in-vitro, and in-silico), and found that these alkaloid compounds have significant antiviral properties against several infectious viruses. These alkaloids repressed and targeted various important stages of viral infection at non-toxic doses while some of the alkaloids reported here also exhibited comparable inhibitory activities to commercially used drugs. Overall, these anti-viral effects of alkaloids point to a high degree of specificity, implying that they could serve as effective and safe antiviral medicines if further pursued in medicinal and pharmacological investigations.

The HRA2pl fusion peptide exerts in vitro antiviral activity against human respiratory paramyxoviruses and pneumoviruses

Acute respiratory infections are a group of diseases caused by viruses, bacteria, and parasites that mainly affect children until the age of 5 and immunocompromised senior adults. In Mexico, these infections are the main cause of morbidity in children, with more than 26 million cases of respiratory infections reported by the Secretariat of Health, in 2019. The human respiratory syncytial virus (hRSV), the human metapneumovirus (hMPV), and the human parainfluenza-2 (hPIV-2) are responsible for many respiratory infections. Currently, palivizumab, a monoclonal antibody against the fusion protein F, is the treatment of choice against hRSV infections. This protein is being studied for the design of antiviral peptides that act by inhibiting the fusion of the virus and the host cell. Therefore, we examined the antiviral activity of the HRA2pl peptide, which competes the heptad repeat A domain of the F protein of hMPV. The recombinant peptide was obtained using a viral transient expression system. The effect of the fusion peptide was evaluated with an in vitro entry assay. Moreover, the effectiveness of HRA2pl was examined in viral isolates from clinical samples obtained from patients with infections caused by hRSV, hMPV, or hPIV-2, by evaluating the viral titer and the syncytium size. The HRA2pl peptide affected the viruses' capacity of entry, resulting in a 4-log decrease in the viral titer compared to the untreated viral strains. Additionally, a 50% reduction in the size of the syncytium was found. These results demonstrate the antiviral potential of HRA2pl in clinical samples, paving the way toward clinical trials.

Respiratory Syncytial Virus Incidence and Severity in a Community-Based Prospective Cohort of Children Aged 0-14 Years

BACKGROUND

Respiratory syncytial virus (RSV) is a substantial source of severe illnesses including acute lower respiratory infections (ALRIs) like pneumonia. However, its burden in older children remains less well understood.

METHODS

Using a community-based prospective cohort, we assessed the burden of symptomatic reverse-transcription polymerase chain reaction-confirmed RSV among Nicaraguan children aged 0-14 years from 2011 to 2016. ALRI was defined as physician diagnosis of pneumonia, bronchiolitis, bronchitis, or bronchial hyperreactivity.

RESULTS

Between 2011 and 2016, 2575 children participated in the cohort. Of these, 630 (24.5%) had at least 1 episode of symptomatic RSV and 194 (7.5%) had multiple episodes. Subtype was identified in 571 (69.3%) episodes with 408 (71.5%) RSV-A, 157 (27.5%) RSV-B, and 6 (1%) positive for both. Children aged <2 years displayed the highest incidence of symptomatic RSV, with 269.3 cases per 1000 person-years (95% confidence interval [CI], 242.1-299.5). Beyond 2 years, incidence (95% CI) of symptomatic RSV decreased rapidly: 145.6 (129.9-163.1), 37.9 (31.9-45.0), and 19.3 (14.9-25.0) cases per 1000 person-years among children aged 2-4, 5-9, and 10-14 years, respectively. Incidence of RSV-associated ALRI was highest in children aged <2 years (85.95 per 1000 person-years [95% CI, 71.30-103.61]): 2.1, 9.5, and 17.3 times that of participants aged 2-4, 5-9, and 10-14 years, respectively. Children <2 years old were significantly more likely to have an RSV-associated hospitalization (P < .001).

CONCLUSIONS

There is a substantial burden of symptomatic and severe RSV in children. While older children did present with RSV, the rates of symptomatic and severe RSV decreased by as much as 95% beyond age 5.

Adult Respiratory Syncytial Virus Infection and Hypoxic Cardiac Arrest—Coexistent or Causal? A Hypothesis-Generating Case Report

Respiratory syncytial virus (RSV) is a well-known pathogen in paediatric patients. However, it also causes substantial morbidity and mortality in adults, posing a major healthcare problem. We present a patient with chronic pulmonary conditions and an acute RSV infection, thus leading to cardiac arrest (CA). We speculate that RSV as the causative agent for CA should be considered in post-resuscitation care. From a wider public health perspective, immuno-naivety for RSV caused by the coronavirus disease 2019 pandemic may induce a severe rise in cases, morbidity, and mortality in the future.

Intramuscular Inoculation of AS02-Adjuvanted Respiratory Syncytial Virus (RSV) F Subunit Vaccine Shows Better Efficiency and Safety Than Subcutaneous Inoculation in BALB/c Mice

We previously explored a panel of adjuvants formulated with pre-fusion RSV-F protein and found that AS02 may be a promising candidate adjuvant for developing RSV-F subunit vaccines with improved immunogenicity and desired immune response type. In this study, we performed a head-to-head comparison of the effect of intramuscular injection to that of subcutaneous injection on the immune response and protective efficacy of recombinant RSV-F subunit vaccine with or without adjuvants (Alhydrogel, squalene-based emulsion adjuvants MF59, AS03, and AS02) in BALB/c mice. After inoculations, antigen-specific antibodies, neutralizing antibodies, antibody subtypes, cytokines, and the persistence of immune response were evaluated. Moreover, challenge tests were also performed to illustrate the possible effect of inoculation routes and adjuvant on virus clearance and histochemistry changes in the lungs of mice. The results indicated that intramuscular inoculation is a more effective and antigen dose-sparing route to enhance the immune response, although subcutaneous inoculation induced faster and stronger IgG antibodies after the initial immunization. Furthermore, adjuvant, but not immunization route, is a more critical factor to affect the humoral/cellular immune response and the immune bias. In addition, adjuvant inoculated via the intramuscular route is safer than that via the subcutaneous route, especially for AS02. This study highlights the importance of the adjuvant and immunization routes in the design and clinical transformation of adjuvanted vaccines. Further investigation is needed to illustrate the mechanism underlying the above difference in both efficiency and safety.

Infection Rate of Respiratory Viruses in the Pandemic SARS-CoV-2 Period Considering Symptomatic Patients: Two Years of Ongoing Observations

BACKGROUND

In the last two years, the SARS-CoV-2 pandemic has determined radical changes in human behaviors and lifestyles, with a drastic reduction in socialization due to physical distancing and self-isolation. These changes have also been reflected in the epidemiological patterns of common respiratory viruses. For this reason, early discrimination of respiratory viruses is important as new variants emerge.

METHODS

Nasopharyngeal swabs of 2554 patients, with clinically suspected Acute Respiratory Infections (ARIs) from October 2019 to November 2021, were collected to detect 1 or more of the 23 common respiratory pathogens, especially viruses, via BioFilmArray RP2.1plus, including SARS-CoV-2. Demographical characteristics and epidemiological analyses were performed as well as a laboratory features profile of positive patients.

RESULTS

An observational study on 2300 patients (254 patients were excluded because of missing data) including 1560 men and 760 women, median age of 64.5 years, was carried out. Considering the respiratory virus research request, most of the patients were admitted to the Emergency Medicine Department (41.2%, of patients), whereas 29.5% were admitted to the Infectious Diseases Department. The most frequently detected pathogens included SARS-CoV-2 (31.06%, 707/2300, from March 2020 to November 2021), InfA-B (1.86%, 43/2300), HCoV (2.17% 50/2300), and HSRV (1.65%, 38/2300). Interestingly, coinfection rates decreased dramatically in the SARS-CoV-2 pandemic period. The significative decrease in positive rate of SARS-CoV-2 was associated with the massive vaccination.

CONCLUSION

This study represents a dynamic picture of the epidemiological curve of common respiratory viruses during the two years of pandemic, with a disregarded trend for additional viruses. Our results showed that SARS-CoV-2 had a preferential tropism for the respiratory tract without co-existing with other viruses. The possible causes were attributable either to the use of masks, social isolation, or to specific respiratory receptors mostly available for this virus, external and internal lifestyle factors, vaccination campaigns, and emergence of new SARS-CoV-2 variants.

Advances in Infectious Disease Vaccine Adjuvants

Vaccines are one of the most significant medical interventions in the fight against infectious diseases. Since their discovery by Edward Jenner in 1796, vaccines have reduced the worldwide transmission to eradication levels of infectious diseases, including smallpox, diphtheria, hepatitis, malaria, and influenza. However, the complexity of developing safe and effective vaccines remains a barrier for combating many more infectious diseases. Immune stimulants (or adjuvants) are an indispensable factor in vaccine development, especially for inactivated and subunit-based vaccines due to their decreased immunogenicity compared to whole pathogen vaccines. Adjuvants are widely diverse in structure; however, their overall function in vaccine constructs is the same: to enhance and/or prolong an immunological response. The potential for adverse effects as a result of adjuvant use, though, must be acknowledged and carefully managed. Understanding the specific mechanisms of adjuvant efficacy and safety is a key prerequisite for adjuvant use in vaccination. Therefore, rigorous pre-clinical and clinical research into adjuvant development is essential. Overall, the incorporation of adjuvants allows for greater opportunities in advancing vaccine development and the importance of immune stimulants drives the emergence of novel and more effective adjuvants. This article highlights recent advances in vaccine adjuvant development and provides detailed data from pre-clinical and clinical studies specific to infectious diseases. Future perspectives into vaccine adjuvant development are also highlighted.

Innate Immune Responses by Respiratory Viruses, Including Rhinovirus, During Asthma Exacerbation

Viral infection, especially with rhinovirus (RV), is a major cause of asthma exacerbation. The production of anti-viral cytokines such as interferon (IFN)-β and IFN-α from epithelial cells or dendritic cells is lower in patients with asthma or those with high IgE, which can contribute to viral-induced exacerbated disease in these patients. As for virus-related factors, RV species C (RV-C) induces more exacerbated disease than other RVs, including RV-B. Neutrophils activated by viral infection can induce eosinophilic airway inflammation through different mechanisms. Furthermore, virus-induced or virus-related proteins can directly activate eosinophils. For example, CXCL10, which is upregulated during viral infection, activates eosinophils in vitro. The role of innate immune responses, especially type-2 innate lymphoid cells (ILC2) and epithelial cell-related cytokines including IL-33, IL-25, and thymic stromal lymphopoietin (TSLP), in the development of viral-induced airway inflammation has recently been established. For example, RV infection induces the expression of IL-33 or IL-25, or increases the ratio of ILC2 in the asthmatic airway, which is correlated with the severity of exacerbation. A mouse model has further demonstrated that virus-induced mucous metaplasia and ILC2 expansion are suppressed by antagonizing or deleting IL-33, IL-25, or TSLP. For treatment, IFNs including IFN-β suppress not only viral replication but also ILC2 activation in vitro. Agonists of toll-like receptor (TLR) 3 or 7 can induce IFNs, which can then suppress viral replication and ILC2 activation. Therefore, if delivered in the airway, IFNs or TLR agonists could become innovative treatments for virus-induced asthma exacerbation.

Protective mechanism of quercetin and its derivatives in viral-induced respiratory illnesses

Globally, acute respiratory illnesses are the most commonly manifesting illness in all age group. The disease mostly affects the upper respiratory tract (URT) and is self-limiting. However, a small percentage progresses to lower respiratory tract infections (LRTI). The most important causative agents of severe LRTIs are bacteria and viruses. Various viruses can cause respiratory tract infections, being the most essential belonging to the Orthomyxoviridae, Paramyxoviridae, Picornaviridae, coronaviruses, and adenoviruses. Quercetin is classified as a flavonoid compound and was previously known to have antiviral, antibacterial, antioxidant, and anti-inflammatory activities. Some preclinical studies highlight quercetin could also interfere with coronavirus infection and modulate the release of pro-inflammatory cytokines. Since there is no comprehensive compilation addressing the antiviral activities of quercetin and its derivatives, this narrative review provides a summary of the preclinical evidence of their antiviral activities on respiratory illnesses induced by viruses other than coronaviruses. The literature research was performed in PubMed, Scopus, and Google Scholar. The results explain that quercetin has a wide range of actions in viral-induced respiratory illnesses including, but not limited to suppressing pro-inflammatory cytokines and chemokines, promoting antioxidant-related genes expression, blocking viral entry and replication, accelerating viral clearance, reducing the accumulation of alveolar macrophages, and reducing goblet cells marker and mucin gene expression.