Viral-Induced Wheeze and Asthma Development

Recurrent wheezing illnesses in infancy are often the first sign of asthma. Most episodes are initiated by viral infections, and airway bacteria also contribute. Viral respiratory infections are universal during infancy, but only a subset of infants develop illnesses with wheezing. Risk factors for wheezing illnesses include small lung size, prematurity, and exposure to tobacco smoke. Most children with recurrent wheezing improve with time, but approximately one-third of infants with recurrent wheeze go on to develop asthma. There is great interest in identifying which infants are at risk for asthma, so that efforts at prevention can be directed toward those who might benefit the most. Factors related to the progression from recurrent wheezing to asthma include those related to the host, pathogen, and environment or lifestyle. Early onset of atopy is an important host factor, and children who become sensitized to multiple allergens in early life are at greatest risk. Children who wheeze with rhinoviruses are also likely to develop asthma, and this is especially true for atopic children. These associations are well established, but whether viral illnesses cause asthma is controversial. Clinical studies have identified predisposing factors such as low lung function and atopy that promote virus-induced wheezing illnesses. In addition, there is evidence from intervention studies that virus-induced damage to the airways can cause recurrent wheezing in some children. These relationships are not mutually exclusive, and it is likely that both apply to the relationship between virus-induced wheezing illnesses and asthma. The implications are that antiviral strategies as well as those targeting atopy and promoting lung development may be useful to prevent childhood asthma.