Asthma during the first years of life and its relation to viral infections

The biggest risk for the appearance of episodes of wheezing in infants and children comes from the infections by respiratory viruses. The viruses most frequently responsible of wheezing in this group are the respiratory syncytial virus (RSV) and the human metapneumovirus. In school aged children and teenagers the rhinoviruses have the main role. The bronchiolitis (BQL) by RSV is cause of hospitalization in 1-2% of children younger than two in each autumn and winter season. Its clinical expression is very different and probably related with genetic factors and the neurological and immune response in mucosal airway of the affected kid. The BQL clinically important is associated with wheezing and asthma during the following years. In the BQL and later recurrent wheezing an incremented production of leukotrienes has been demonstrated. Molecules able to avoid its liberation or to neutralise its effects can have good effects in the asthma after the bronchiolitis, started most of the time by viruses. In the handling of the asthma leaded by viruses in infants and preschoolers, inhaled corticosteroids have demonstrated effectiveness limited to the active course period, but they can have some repercussions in the growth of the affected kid. The idea of being able to modify the natural course of the illness with the early establishment of breathed steroids has not been confirmed with the studies now available. Montelukast, a receptor antagonist of leukotrienes, has demonstrated a partial control of the symptoms that frequently remain after the bronchiolitis by RSV. The use of this medicine in the recurrent wheezing in infants and preschoolers has demonstrated clinical benefits without any significant adverse effects. Influenza immunization in children at risk and a good control of the asthmatic illness are good strategies, with the aim of facing better conditions in the winter season when respiratory infections origin numerous acute asthmatic exacerbations. Our knowledge of asthma relapses is incomplete, because of the difficulties to understand the interactions between the different starting agents (viruses, allergens, pollution, weather) but to deepen in it will give chances for the therapeutic intervention.