The role of viral and bacterial infections on the development and exacerbations of asthma

A considerable proportion of asthma morbidity, mortality and health costs are attributed to asthma exacerbations. Epidemiological studies have convincingly shown that viral respiratory infections are the major causes of asthma exacerbations in both adults and children. Viruses, rhinoviruses in particular, infect the airway epithelium resulting in local and systemic immune responses as well as neural responses, inducing inflammation and airway hyperresponsiveness (AHR). The effects of an infection may vary according to genetic background, the current immune status of the host and parallel environmental stimuli, in addition to the particular infectious agent itself. Moreover, several studies have emphasised the importance of atopy and allergic inflammation in the induction and prolongation of virusinduced respiratory diseases. Identification of the mechanisms involved in the pathogenesis of asthma exacerbations and asthma persistence should facilitate development of future treatments tailored to the underlying cause. © ERS 2012.