[Virus and sensitization]

Respiratory viruses are able to replicate in both the upper and lower respiratory epithelium, thus inducing wheezing. Most clinical studies suggest that wheezing illnesses due to respiratory viruses in early childhood are linked to a risk for asthma. Viruses may induce asthma exacerbations through direct effects on their main target, the respiratory epithelium, as well as via a systemic immune-inflammatory reaction. On other hand, studies have also yielded conflicting results in regard to the ability of viral infection to enhance subsequent allergic responses. Do early viral illnesses cause allergic asthma or viral wheezing episodes serve to reveal children who are already predisposed to this disease on basis of an abnormal lung physiology and/or immune response?