Airway wall eosinophilia is not a feature of equine heaves.

This research aimed to determine whether eosinophils, a type of white blood cell, are found in higher amounts in the airway walls of horses suffering from a chronic respiratory condition called ‘heaves’. It concluded that there were significantly higher eosinophil counts in healthy control horses compared to those with heaves, suggesting that eosinophils do not contribute to the ongoing airway obstruction seen in heaves.

Objectives and Methodology of the Study

• The main objective of this research was to ascertain whether eosinophils infiltrate, or enter, the airway wall structures of horses suffering from a respiratory condition known as heaves.
• Heaves, also known as recurrent airway obstruction, is a common and chronic respiratory disease in horses similar to asthma in humans, characterized by persistent cough, breathing difficulties and decreased performance.
• The researchers examined paraffin-embedded lung tissue samples from six horses identified with heaves who were in crisis (active disease state), and compared these with samples from six healthy horses of a similar age, used as a control group.

Findings of the Study

• The lung tissue samples were stained using Luna’s method, a specific technique used to identify and count eosinophils.
• The total eosinophil counts were determined per square millimeter of basement membrane, a layer of the airway wall.
• The findings depicted that the eosinophil counts were significantly higher in the control horses than in the heaves-afflicted horses.
• The numbers of eosinophils found in the airway’s internal fluids, epithelial cells (cells that line the airways), and airway smooth muscle were also greater in the control horses.

Conclusions of the Study

• The results indicate that eosinophils do not contribute to the persistent airway obstruction observed in heaves, which goes against the common assumption about the role of these cells in chronic inflammatory lung diseases.
• The study challenges the previous belief that eosinophilic inflammation is a significant part of the pathology of heaves in horses and suggests a need for further research to understand the underlying cellular mechanisms of the disease.