Viruses as precipitants of asthma symptoms. I. Epidemiology

Abstract

The epidemiological studies cited have indicated that viruses are commonly associated with wheezing illnesses in populations, in individuals, and in time, but, unlike bacteria, are rarely found during asymptomatic periods. Viruses have been identified in up to 50% of wheezing illnesses and asthma exacerbations occurring in childhood, and in up to 20% of those in adults. In childhood the predominant organisms identified have been rhinoviruses. RSV and parainfluenza viruses, but coronaviruses have not been studied adequately. Wheezing appears to be more common during rhinovirus and RSV than other virus infections in children spontaneously presenting with respiratory infections to medical care, but all virus groups have been incriminated, and in general, wheezing occurs in upwards of 50% of viral infections in asthmatics followed prospectively. The few adult studies available show little difference between viruses in identification rates during wheezing, or propensity to result in wheezing. The predominant viruses change with age, and children with asthma seem to be more prone to symptomatic virus infections than other children, although the presence of atopy alone does not appear to be important. There are important gaps in our knowledge of the epidemiology of virus-associated wheezing attacks, and further prospective studies are required, using early investigation and sensitive methods for identifying rhinoviruses and coronaviruses, to study severe asthma in children and adults. It is hoped that the use of nucleic acid hybridization and newer antigen-detection techniques will improve the ability to identify difficult viruses such as coronaviruses and rhinoviruses in the future. The ability to identify subclinical infections and compare the ratio of subclinical to clinical infections in normal and asthmatic children would be useful but would require intense monitoring of both groups for an extended period (minimum 12 months to cover seasonal variation) with full virological studies every 2-4 weeks-a difficult and expensive task. Another important line of study would be to prospectively document indoor aeroallergen exposure and virus infections in the same individuals, and compare their importance as precipitants of acute severe asthma attacks. With a clearer understanding of the groups at risk for asthma attacks, and the factors which put them at risk and precipitate their attacks, effective preventive strategies will become more feasible.

Murine Cytomegalovirus Infection Alters Th1/Th2 Cytokine Expression, Decreases Airway Eosinophilia, and Enhances Mucus Production in Allergic Airway Disease

“…Studies of individuals with asthma demonstrate a clear correlation between the presence of virus and an increase in asthma symptom scores, an increased need for medication, and a decrease in pulmonary function (reviewed in Ref. 3). Respiratory syncytial virus and parainfluenza virus are common viruses in young children, whereas rhinovirus is a frequent etiological agent in older children and adults (reviewed in Refs.…”

“…Although not widely included in epidemiological studies on asthma, human CMV (HCMV) 3 has been associated with asthma exacerbations in adults (7). HCMV, a ␤ herpesvirus, is recognized as an opportunistic pulmonary pathogen and is a major cause of pneumonia in immunosuppressed bone marrow and lung transplantation recipients (reviewed in Ref.…”

“…Respiratory syncytial virus and parainfluenza virus are common viruses in young children, whereas rhinovirus is a frequent etiological agent in older children and adults (reviewed in Refs. [3][4][5]. However, any virus capable of eliciting an acute respiratory infection has the potential to exacerbate asthma (6).…”

A randomised, double-blind, placebo-controlled study to evaluate the efficacy of oral azithromycin as a supplement to standard care for adult patients with acute exacerbations of asthma (the AZALEA trial)

“…There is little published evidence that standard bacterial infections are important in the aetiology of asthma exacerbations; 14 however, patients with asthma have increased susceptibility to respiratory bacterial infections, [15][16][17] increased carriage of pathogenic respiratory bacteria identified by culture 18 and molecular techniques, 19 and impaired interferon responses to bacterial polysaccharides. 20 In addition, viral infection impairs innate responses that are important in antibacterial immunity 21 and increases bacterial adherence to bronchial epithelial cells.…”

Susceptibility of asthmatic children to respiratory infection

“…Accordingly, the effects of infection on the development of asthma and bronchial hyperreactivity have been exhaustively explored covering both viral and bacterial infections 5,7,[13][14][15][16][17][18]20,23,25,27,30,32 , while the reciprocal, namely the effects of asthma on the development of infection, has been overlooked. Clough and Dow 3 , in an Editorial to Clinical Allergy in 1987, raised the subject but limited themselves to remark that a "hypothesis is that asthmatics may be more at risk of developing respiratory infections".…”