Respiratory viruses in childhood asthma

Association between early viral lower respiratory tract infections and subsequent asthma development

BACKGROUND

The association between hospitalization for human respiratory syncytial virus (HRSV) bronchiolitis in early childhood and subsequent asthma is well established. The long-term prognosis for non-bronchiolitis lower respiratory tract infections (LRTI) caused by viruses different from HRSV and rhinovirus, on the other hand, has received less interest.

AIM

To investigate the relationship between infant LRTI and later asthma and examine the influence of confounding factors.

METHODS

The PubMed and Global Index Medicus bibliographic databases were used to search for articles published up to October 2021 for this systematic review. We included cohort studies comparing the incidence of asthma between patients with and without LRTI at ≤ 2 years regardless of the virus responsible. The meta-analysis was performed using the random effects model. Sources of heterogeneity were assessed by stratified analyses.

RESULTS

This review included 15 articles (18 unique studies) that met the inclusion criteria. LRTIs at ≤ 2 years were associated with an increased risk of subsequent asthma up to 20 years [odds ratio (OR) = 5.0, 95%CI: 3.3-7.5], with doctor-diagnosed asthma (OR = 5.3, 95%CI: 3.3-8.6), current asthma (OR = 5.4, 95%CI: 2.7-10.6), and current medication for asthma (OR = 1.2, 95%CI: 0.7-3.9). Our overall estimates were not affected by publication bias (P = 0.671), but there was significant heterogeneity [I² = 58.8% (30.6-75.5)]. Compared to studies with hospitalized controls without LRTI, those with ambulatory controls had a significantly higher strength of association between LRTIs and subsequent asthma. The strength of the association between LRTIs and later asthma varied significantly by country and age at the time of the interview. The sensitivity analyses including only studies with similar proportions of confounding factors (gender, age at LRTI development, age at interview, gestational age, birth weight, weight, height, smoking exposure, crowding, family history of atopy, and family history of asthma) between cases and controls did not alter the overall estimates.

CONCLUSION

Regardless of the causative virus and confounding factors, viral LRTIs in children < 2 years are associated with an increased risk of developing a subsequent asthma. Parents and pediatricians should be informed of this risk.

Fifteen-minute consultation: An evidence-based approach to the child with preschool wheeze

Preschool wheeze is very common and its prevalence is increasing. It consumes considerable healthcare resources and has a major impact on children and their families due to significant morbidity associated with acute episodes.History taking is the main diagnostic instrument in the assessment of preschool wheeze. Diagnosis and management is complicated by a broad differential and associations with many other diseases and conditions that give rise to noisy breathing, which could be misinterpreted as wheeze. Several clinical phenotypes have been described but they have limitations and do not clearly inform therapeutic decisions. New insights in aetiopathogenesis modify treatment options and lay foundation for further research. An understanding of the approach and available evidence to assess and manage wheeze informs best patient care and use of resources.Our objective is to demonstrate a focused history, examination and management options in a preschool child with wheeze.

The changing face of asthma and its relation with microbes

During the past 50 years, the prevalence of asthma has increased and this has coincided with our changing relation with microorganisms. Asthma is a complex disease associated with local tissue inflammation of the airway that is determined by environmental, immunological, and host genetic factors. In a subgroup of sufferers, respiratory infections are associated with the development of chronic disease and more frequent inflammatory exacerbations. Recent studies suggest that these infections are polymicrobial in nature. Furthermore, there is increasing evidence that the recently discovered asthma airway microbiota may play a critical role in pathophysiological processes associated with the disease. Here, we discuss the current data regarding a possible role for infection in chronic asthma with a particular focus on the role bacteria may play. We discuss recent advances that are beginning to elucidate the complex relations between the microbiota and the immune response in asthma patients. We also highlight the clinical implications of these recent findings in regards to the development of novel therapeutic strategies.

Clinical and epidemiologic phenotypes of childhood asthma

RATIONALE

Clinical and epidemiologic approaches have identified two distinct sets of classifications for asthma and wheeze phenotypes.

OBJECTIVES

To compare epidemiologic phenotype definitions identified by latent class analysis (LCA) with clinical phenotypes based on patient histories, diagnostic work-up, and treatment responses. To relate phenotypes to genetic and environmental determinants as well as diagnostic and treatment-related parameters.

METHODS

LCA was performed in an international multicenter birth cohort based on yearly questions about current wheeze until age 6 years. Associations of wheeze classes and clinical phenotypes with asthma-related characteristics such as atopy, lung function, fraction of exhaled nitric oxide, and medication use were calculated using regression models.

MEASUREMENTS AND MAIN RESULTS

LCA identified five classes, which verified the clinically defined wheeze phenotypes with high sensitivity and specificity; the respective receiver operating characteristics curves displayed an area under the curve ranging from 84% (frequent wheeze) to 85% (asthma diagnosis) and 87% (unremitting wheeze) to 97% (recurrent unremitting wheeze). Recurrent unremitting wheeze was the most specific and unremitting wheeze at least once the most sensitive definition. The latter identified a subgroup of children with decreased lung function, increased genetic risk, and in utero smoke exposure (ODDS RATIO, 2.03; 95% CONFIDENCE INTERVAL, 1.12-3.68; P = 0.0191), but without established asthma diagnosis and treatment.

CONCLUSIONS

Clinical phenotypes were well supported by LCA analysis. The hypothesis-free LCA phenotypes were a useful reference for comparing clinical phenotypes. Thereby, we identified children with clinically conspicuous but undiagnosed disease. Because of their high area under the curve values, clinical phenotypes such as (recurrent) unremitting wheeze emerged as promising alternative asthma definitions for epidemiologic studies.

Role of infections in the induction and development of asthma: genetic and inflammatory drivers

Genetic and environmental factors interact to initiate and even maintain the course of asthma. As one of the highly risky environmental factors, infections in predisposed individuals can promote asthma development and exacerbations and/or prolong symptoms. This review will describe our current understanding of the genetic markers of innate immunity in the induction and development of asthma, the diverse roles of infections in modulating allergic inflammation, host susceptibility to infections and subsequent acute exacerbations in an allergic setting, and the therapeutic or preventive implications of existing knowledge. Current challenges and future directions in basic and clinical research of asthma are also discussed.

The management of pre-school wheeze

Wheeze, a common symptom in pre-school children, is a continuous high-pitched sound, with a musical quality, emitting from the chest during expiration. A pragmatic clinical classification is episodic (viral) wheeze and multiple-trigger wheeze. Diagnostic difficulties include other conditions that give rise to noisy breathing which could be misinterpreted as wheeze. Most preschool children with wheeze do not need rigorous investigations. Primary prevention is not possible but avoidance of environmental tobacco smoke exposure should be strongly encouraged. Bronchodilators provide symptomatic relief in acute wheezy episodes but the evidence for using oral steroids is conflicting for children presenting to the Emergency Department [ED]. Parent initiated oral steroid courses cannot be recommended. High dose inhaled corticosteroids [ICS] used intermittently are effective in children with frequent episodes of moderately severe episodic (viral) wheeze or multiple-trigger wheeze, but this associated with short term effects on growth and cannot be recommended as a routine. Maintenance treatment with low to moderate continuous ICS in pure episodic (viral) wheeze is ineffective. Whilst low to moderate dose regular ICS work in multi-trigger wheeze, the medication does not modify the natural history of the condition. Even if there is a successful trial of treatment with ICS, a break in treatment should be given to see if the symptoms have resolved or continuous therapy is still required. Maintenance as well as intermittent Montelukast has a role in both episodic and multi trigger wheeze. Good multidisciplinary support and education is essential in managing this common condition.

Bacterial infections and pediatric asthma

Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis seem to have no role in asthma in children. Mycoplasma pneumoniae and Chlamydophila pneumoniae can induce wheezing and cause asthma exacerbations in children, and chronic Chlamydophila infections may even participate in asthma pathogenesis. However, studies have failed to show any benefits from antibiotics for incipient or stable pediatric asthma, as well as for asthma exacerbations in children. Exposure to antibiotics in infancy has been an independent risk factor of later asthma in many studies. A recent study applying molecular biology methods to lower airway samples provided preliminary evidence that lower airways are not sterile but have their own protective microbiota, which can be disturbed in lung diseases like asthma.

The Human Lung Microbiome

The human lower respiratory tract is considered sterile in normal healthy individuals (Flanagan et al., 2007; Speert, 2006) despite the fact that every day we breathe in multiple microorganisms present in the air and aspirate thousands of organisms from the mouth and nasopharynx. This apparent sterility is maintained by numerous interrelated components of the lung physical structures such as the mucociliary elevator and components of the innate and adaptive immune systems (discussed below) (reviewed in (Diamond et al., 2000; Gerritsen, 2000)). However, it is possible that the observed sterility might be a result of the laboratory practices applied to study the flora of the lungs. Historically, researchers faced with a set of diseases characterized by a changing and largely cryptic lung microbiome have lacked tools to study lung ecology as a whole and have concentrated on familiar, cultivatable candidate pathogens.

Do early-life viral infections cause asthma?

Epidemiologic associations between viral lower respiratory infections (LRIs) and asthma in later childhood are well known. However, the question of whether such infections cause asthma or unmask asthma in a susceptible host has still not been settled. Most early evidence centered on the role of the respiratory syncytial virus; however, recent studies highlight a potential role for human rhinovirus as a risk factor for asthma. The links between early-life viral LRI and subsequent asthma are generally via wheeze; however, the presence of wheeze does not give any information about why the child is wheezing. Wheeze in early life is, at best, a fuzzy phenotype and not specific for subsequent asthma. The risk of asthma after viral LRI is increased in the presence of allergic sensitization in early life and if the infection is more severe. Atopy-associated mechanisms also appear to be involved in viral-induced acute exacerbations of asthma, especially in prolonging symptomatology after the virus has been cleared from the lungs. Breaking the nexus between viral respiratory infections and asthma may be possible with interventions designed to inhibit atopy-related effectors mechanisms from participating in the host response to respiratory viral infections.

Role of respiratory pathogens in infants hospitalized for a first episode of wheezing and their impact on recurrences

In order to evaluate the infectious agents associated with the first episode of severe acute wheezing in otherwise healthy infants and to define the role of each of them in recurrences, 85 patients in Italy, aged <12 months, hospitalized because of a first acute episode of wheezing, were prospectively enrolled between 1 October 2005 and 31 March 2006. Upon enrollment, nasopharyngeal swabs were collected for the real-time PCR detection of respiratory syncytial virus (RSV) types A and B, influenza virus types A and B, adenovirus, parainfluenza viruses types 1, 2, 3 and 4, rhinovirus, human metapneumovirus, human coronavirus types 229E, OC43, NL63, and HKU1, bocavirus, enterovirus, and paraechovirus; nasopharyngeal aspirates were also obtained to detect atypical bacteria. At least one infectious agent was identified in 76 children (89.4%). RSV was the most frequently detected pathogen and its prevalence was significantly higher than that of the other pathogens in both age groups, and significantly higher in the children aged 3-12 months than in those aged <3 months. Only the children with RSV infection experienced recurrent wheezing. Viral load was significantly higher in children with than in those without recurrent wheezing. This study shows that RSV is the main reason for hospitalization during the first wheezing episode in infants, and that it appears to be the only pathogen associated with a high frequency of recurrences. A high viral load seems to be strictly related to the likelihood of recurrence.

Kinetics of antibody-induced modulation of respiratory syncytial virus antigens in a human epithelial cell line

Background

The binding of viral-specific antibodies to cell-surface antigens usually results in down modulation of the antigen through redistribution of antigens into patches that subsequently may be internalized by endocytosis or may form caps that can be expelled to the extracellular space. Here, by use of confocal-laser-scanning microscopy we investigated the kinetics of the modulation of respiratory syncytial virus (RSV) antigen by RSV-specific IgG. RSV-infected human epithelial cells (HEp-2) were incubated with anti-RSV polyclonal IgG and, at various incubation times, the RSV-cell-surface-antigen-antibody complexes (RSV Ag-Abs) and intracellular viral proteins were detected by indirect immunoflourescence.

Results

Interaction of anti-RSV polyclonal IgG with RSV HEp-2 infected cells induced relocalization and aggregation of viral glycoproteins in the plasma membrane formed patches that subsequently produced caps or were internalized through clathrin-mediated endocytosis participation. Moreover, the concentration of cell surface RSV Ag-Abs and intracellular viral proteins showed a time dependent cyclic variation and that anti-RSV IgG protected HEp-2 cells from viral-induced death.

Conclusion

The results from this study indicate that interaction between RSV cell surface proteins and specific viral antibodies alter the expression of viral antigens expressed on the cells surface and intracellular viral proteins; furthermore, interfere with viral induced destruction of the cell.