Cellular basis of chronic obstructive pulmonary disease in horses.

This study investigates the cellular basis of chronic obstructive pulmonary disease (COPD) in horses, a condition characterized by allergic reactions in the airways triggered by various substances, often fungi found in low-quality hay or straw bedding. It significantly reduces the physical capabilities of affected horses and is marked by bronchitis, emphysema, and increased immune response in the lungs and lymph nodes.

Characteristics of COPD in Horses

• The study particularly notes that COPD is a significant inflammatory obstructive disease found predominantly in middle-aged horses, resulting in recurrent breathing difficulties, continued coughing, and diminished athletic and work performance.
• This condition often triggers hypersensitive reactions in the airway tissues when horses are exposed to allergens, most commonly to various types of fungi including Saccharopolyspora rectivirgula, Aspergillus fumigatus, and Thermoactinomyces vulgaris, which are usually found in hay and straw of poor quality.

Physical and Pathological Findings

• The physically observed conditions in COPD stricken horses are a loss of lung flexibility, also known as pulmonary emphysema, and non-collapsible lungs.
• Upon microscopic examination, the presence of chronic bronchitis/bronchiolitis was frequently detected, featuring discernible changes in the structure of the lungs’ interior air passages, their mucous lining, the underlying layers, and smooth muscle layer.
• Another common microscopic finding was alveolar emphysema in all its forms, which represents accumulated air pockets in the lungs that affect its elasticity and cause problems in breathing.

Immunoreactivity and Cytology

• An elevated immunoreactive response was recorded in the lungs and tracheobronchial lymph nodes of the affected horses, indicating an active immune response toward the disease.
• The cell populations present in the bronchial bifurcations were primarily desquamated airway epithelial cells along with eosinophils, neutrophils, mast cells, red blood cells, and alveolar macrophages which all contribute to the disease’s manifestation.
• Notably, the presence of Curschmann’s spirals, which are a type of mucus plug, was discovered confirming the presence of COPD.

Bacterial Findings

• Lung samples exhibited the presence of primary pulmonary pathogens, potential contaminants and secondary infection agents, which could further complicate the existing COPD.

Key Findings

• All these findings highlight that chronic bronchitis and bronchiolitis form the foundational layer of COPD and it has an inflammatory and immunological origin.
• The study emphasizes that the condition of emphysema often seen in COPD-affected horses is secondary and likely caused due to airway obstructions.