CHAPTER 31: LOWER RESPIRATORY TRACT DISEASE
Lower Respiratory Tract Diseases
Small Airway Inflammatory Disease (SAID)
Small airway inflammatory disease (SAID) affects the secondary bronchi &
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Infection, allergens or chemicals irritate the endothelium of the bronchioles causing the goblet cells of the submucosal glands to produce and secrete excess into the lumen of the airway. This partially obstructs airflow causing turbulence and increased resistance to airflow in the lungs. Irritation also causes inflammation of endothelial cells and triggers the widespread release of from mast cells. Histamine causes hypertrophy of the airway wall and bronchiospasm, further narrowing the airway. Chronically, the inflammation causes a decrease in the elasticity of the airway walls and fibrosis of the respiratory endothelium, predisposing the horse to chronic obstructive pulmonary disease, exercise induced pulmonary haemorrhage and infection as the airways become progressively fragile. Young performance horses are most susceptible to SAID. This may be related to the high incidence of respiratory infection seen in performance horses or may be related to the stress of trailering and competition. The clinical presentation of SAID includes coughing, exercise intolerance, poor performance and expectoration. Diagnosis is made through clinical signs and symptoms, endoscopy revealing inflammation of the respiratory endothelium and increased mucus production and transtracheal aspirate (TA) or bronchial lavage (BAL) revealing increased mucus and histamine production without infection. Treatment of SAID involves the removal of the irritating substance as well as the administration of inhaled corticosteroids and . Prognosis is poor as it is often impossible to isolate and remove every cause of respiratory irritation and damage to the walls of the airways quickly becomes permanent.
Allergic Rhinitis and Allergic Bronchitis (Allergies)
Allergic rhinitis and allergic bronchitis often occur together and are commonly called “allergies”. Rhinitis is a term indicating the inflammation of the mucosa of the nasal cavities while bronchitis indicated inflammation of the mucosa of the bronchi and bronchioles. The inflammation is triggered by the presence of a large, protein-based molecule in the respiratory tract. The molecule acts as a pathogen that triggers a localized type hypersensitivity reaction in the mucosa of the airways.
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