Role of Infection in the Development and Exacerbation of Asthma

From Expert Review of Respiratory Medicine
Theresa W Guilbert; Loren C Denlinger

Posted: 03/02/2010; Expert Rev Resp Med. 2010;4(1):71-83. © 2010 Expert Reviews Ltd.

Abstract
Respiratory infections are associated with wheezing illnesses in all ages and may also impact the development and severity of asthma.
Respiratory tract infections caused by viruses, Chlamydophila or Mycoplasma have been hypothesized to have significant roles in the pathogenesis of asthma.
Progress is being made toward establishing the mechanisms by which these agents can cause acute wheezing and impact the pathophysiology of asthma.
Host factors probably contribute to the risk of asthma inception and exacerbation, and these contributions may also vary with respect to early- versus adult-onset disease. This review discusses these various associations as they pertain to the development and exacerbation of asthma.

Introduction
Respiratory infections are associated with wheezing illnesses at all ages and may also impact the development and severity of asthma. Respiratory tract infections caused by viruses, Chlamydophila or Mycoplasma have been hypothesized to have significant roles in the pathogenesis of asthma.
Of these respiratory pathogens, viruses have been shown to be epidemiologically associated with asthma in several ways.
First, particular viruses associated with infantile wheezing have been theorized to lead to the inception of the asthmatic phenotype.
Second, children who experience severe viral respiratory infections in early life are more likely to have asthma later in childhood.
Furthermore, in children and adults with established asthma, viral upper respiratory tract infections (URIs) play a key role in producing acute exacerbations that may lead to healthcare utilization.
Several host factors, such as allergic sensitization and virus-induced interferon responses, modify the risk of virus-induced wheezing.

For infections with other microbes, interest has focused on Chlamydophila and Mycoplasma as possible contributors to both acute exacerbations and the severity of chronic asthma.
Finally, colonization of the upper airways in infancy with common bacterial pathogens has been demonstrated to increase the risk of subsequent asthma. We review these various associations as they pertain to the development and exacerbation of asthma.