Criteria for development of animal models of diseases of the respiratory system: the comparative approach in respiratory disease model development.
Advances in the understanding of human respiratory disease can come from careful clinical studies of the diseases as they occur in man, but such studies are naturally limited in terms of experimental manipulation. In the last 2 decades, an increasingly complex plethora of experimental respiratory disease models has been developed and utilized by investigators, but relatively less attention has been paid to the naturally occurring pulmonary diseases of animals as potential models. This paper is aimed at presenting selected examples of spontaneous pulmonary disease in animals that may serve as exploitable models for human chronic bronchitis, bronchiectasis, emphysema, interstitial lung disease, hypersensitivity pneumonitis, hyaline membrane disease, and bronchial asthma. Chronic bronchitis in dogs is characterized by chronic cough, excessive mucus production, and chronic inflammatory changes in bronchial walls. The disease affects mainly smaller-breed dogs of middle age or older. Equine chronic bronchitis tends to be a small airway disease with marked goblet cell proliferation and excessive mucus production, which may be accompanied by alveolar emphysema. Many animals develop bronchiectasis or bronchiolitis obliterans secondary to chronic suppurative bronchopneumonia, but chronic respiratory disease (CRD) of rats may be the most useful model of bronchiectasis. Models for emphysema must include actual alveolar destruction and ideally should be accompanied by appropriate pathophysiologic decrements. Many animals occasionally develop emphysema, but the disease has not been well documented, except possibly in horses. The interstitial lung diseases of man represent a complicated and poorly understood group of entities and near-entities. The same is true for animals, although interstitial lung disease in animals is much less common than bronchopneumonia. Cattle seem prone to develop interstitial lesions. Proliferative interstitial pneumonia of cattle includes many morphologic similarities to the spectrum of human interstitial pneumonitides. Fibrosing alveolitis of cattle is a morphologic end point that may have its origins in different forms of interstitial injury. Hypersensitivity pneumonitis has been best detailed in cattle and in horses and is clinically, etiologically, immunologically, and morphologically similar to the disease in man. Hyaline membrane disease has been poorly documented in animals, with the possible exception of the neonatal respiratory distress syndromes of foals and piglets. Bronchial asthma is similarly not well established as a spontaneous disease in animals, although experimental models exist. Eosinophilic bronchiolitis of cattle may represent a useful asthma model but has been poorly detailed. In order to make them useful as models, more attention should be paid to detailing the clinical, morphologic, and etiologic aspects of these naturally occurring animal pulmonary diseases.