Abstract
Chronic obstructive pulmonary disease (COPD) is characterized by chronic airway inflammation and/or airflow limitation due to pulmonary emphysema. Chronic bronchitis, pulmonary emphysema, and bronchial asthma may all be associated with airflow limitation; therefore, exacerbation of asthma may be associated with the pathophysiology of COPD. Furthermore, recent studies have suggested that the exacerbation of asthma, namely virus-induced asthma, may be associated with a wide variety of respiratory viruses. COPD and asthma have different underlying pathophysiological processes and thus require individual therapies. Exacerbation of both COPD and asthma, which are basically defined and diagnosed by clinical symptoms, is associated with a rapid decline in lung function and increased mortality. Similar pathogens, including human rhinovirus, respiratory syncytial virus, influenza virus, parainfluenza virus, and coronavirus, are also frequently detected during exacerbation of asthma and/or COPD. Immune response to respiratory viral infections, which may be related to the severity of exacerbation in each disease, varies in patients with both COPD and asthma. In this regard, it is crucial to recognize and understand both the similarities and differences of clinical features in patients with COPD and/or asthma associated with respiratory viral infections, especially in the exacerbative stage. In relation to definition, epidemiology, and pathophysiology, this review aims to summarize current knowledge concerning exacerbation of both COPD and asthma by focusing on the clinical significance of associated respiratory virus infections.
Highlights
Asthma and chronic obstructive pulmonary disease (COPD) are very common inflammatory diseases of the airways
In the case of COPD, World Health Organization (WHO) consensus reports forecast that this disorder will be ranked the third cause of mortality in the world by 2020 (Global initiative for chronic obstructive lung disease [GOLD], 20131)
This review aims to summarize the clinical aspects of exacerbations in asthma and COPD from the perspective of the definition of exacerbations, epidemiology, and pathophysiology, with a special focus on the clinical significance of the presence of respiratory viruses
Summary
Asthma and chronic obstructive pulmonary disease (COPD) are very common inflammatory diseases of the airways. In the case of COPD, WHO consensus reports forecast that this disorder will be ranked the third cause of mortality in the world by 2020 (Global initiative for chronic obstructive lung disease [GOLD], 20131). Respiratory viral infections are common and usually selflimiting illnesses in healthy adults and a major cause of exacerbations in patients with asthma (Figure 1) and/or COPD (Figure 2). PATHOPHYSIOLOGY OF ASTHMA AND COPD Asthma and COPD are prevalent chronic pulmonary diseases characterized by chronic airway inflammation and airflow limitation. Airway inflammation in asthma is characterized by allergic phenotypes, such as dense infiltration of eosinophils and T helper type 2 lymphocytes, associated with atopic status, while that of COPD is mainly accumulation of neutrophils, CD8positive cytotoxic T cells, and activated macrophages, which are caused by inhalation of harmful substances, such as smoking. With respect to the site of inflammation, asthma involves predominantly larger airways, while in COPD, inflammation affects predominantly small airways and the lung parenchyma, characterized as irreversible airway narrowing because of fibrosis around the small www.frontiersin.org
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