The role of viral infection in the etiology and pathogenesis of chronic bronchitis and emphysema, with consideration of a naturally occurring animal model.

Before discussing an animal model for chronic bronchitis and emphysema I will direct a few remarks to some of the special aspects of the problems which this disease presents. Also, I should like to review briefly the more pertinent studies that have been concerned with the possible role of viral infections in the etiology and pathogenesis of chronic bronchitis and emphysema. In the first place, largely because of ignorance of etiology and pathogenesis, this disease, or group of diseases, is hard to define. The clinical concept of chronic bronchitis, as diagnosed by a history of productive cough, without specific lung disease, existing for an arbitrarily chosen period of time is now commonly accepted.12 So, too, is the concept of emphysema, defined at the Ciba Symposium of 1959, as a "condition of the lung characterized by increase beyond the normal in the size of air spaces distal to the terminal bronchiole either from dilatation or from destruction of their walls."2 Many pathologists, however, now insist that the definition include only conditions in which there are destructive changes in the alveolar walls, as set forth in a statement of the American Thoracic Society.' Such definitions, unfortunately, are not very valuable from a clinical viewpoint. Moreover, since there still are so many differences of opinion concerning clinical diagnosis and definition it would seem useful, for practical purposes, to define this syndrome by describing a typical case. A prototype, as depicted in Table 1, would be a middle-aged man, a heavy cigarette smoker for years, who has a chronic productive cough; acute exacerbations, often initiated by upper respiratory infections, commonly occur, especially during the winter. Dyspnea, signs of airway obstruction, and impairment of ventilatory capacity develop sooner or later. Chest X-rays usually are