ABSTRACT
The major clinical symptoms of asthma are paroxysms of dyspnea, wheezing, and cough. These symptoms vary from mild to severe and may even be unremitting (status asthmaticus). A characteristic feature of most asthmatic patients is that their airways have an increased tendency to narrow on exposure to a variety of chemical, pharmacological, or physical stimuli, a phenomenon called "airway hyperresponsiveness.'' Although its etiology is still unclear, it is well known that viral respiratory infections can induce or aggravate airway hyperresponsiveness. A number of excellent reviews have been written on virus-induced airway hyperresponsiveness from a clinical point of view (1-6). However, most of the basic research concerning this issue has been performed in animals. Airway dysfunction after a viral infection has been measured in a variety of animal species, including the mouse (7), rat (8,9), guinea pig (I 0-17), ferret ( 18), feline ( 19), dog (20,21), lamb (22,23), and calf (24). In most of the studies human-relevant viruses were used, like parainfluenza (PI) virus (8, 10-15, 17 ,25), influenza virus (7,21,26), adenoviruses (27), and respiratory syncytial virus (RSV) (9,22-24,28). The onset of airway dysfunction is observed as soon as 2-3 days after infection in the mouse, feline, and dog ( 19,25,29), and airway hyperresponsiveness was
130 Folkerts et a/.
