Cytology of tracheobronchial aspirates in horses.

This study examines types of cells found in tracheobronchial aspirates (fluid samples) in horses, comparing results from healthy horses and those with respiratory diseases. The findings show that aspirates from sick horses often contain different cells and more mucus than those from healthy horses. Interestingly, some horses without visible lung disease symptoms still had inflammation indicated in their aspirate samples, on further examination.

Method of Study

• The study used tracheobronchial aspirates obtained from a total of 84 horses comprising 27 normal horses and 57 horses with various respiratory diseases.

Findings in Healthy Horses

• The aspirates from the healthy horses mainly contained ciliated columnar epithelial cells and mononuclear cells, along with a few neutrophils, and mucus. These cell types are expected in healthy lung tissue.

Findings in Horses With Respiratory Disease

• In horses with acute suppurative bronchopneumonias or chronic bronchiolitis, the aspirates had predominantly neutrophils, which are a type of white blood cell indicative of inflammation or infection, and usually large amounts of mucus.
• In cases of severe suppurative inflammatory diseases, many of the cells were degenerated, indicating tissue damage, and there were coils of fibrinous material similar to Curschmann’s spirals, a feature seen in human diseases like asthma.
• Eosinophils were rarely found in the samples, even from horses with histories suggesting allergic respiratory disease. This is a crucial finding as eosinophils are often associated with allergic reactions in other species.
• Horses with epistaxis (nosebleeds) often had macrophages with intracytoplasmic green globules (hemosiderin). Hemosiderin comes from the breakdown of blood and its presence in macrophages suggests that these immune cells are cleaning up after some sort of bleeding or damage.

Subclinical Lung Disease

• The test occasionally revealed lung disease in horses that showed no clinical symptoms of the disease. This included four horses that displayed no clinical signs of lung disease and whose lungs appeared normal on percussion and auscultation, but whose aspirates suggested inflammation.
• Further histologic examination of these asymptomatic horses confirmed bronchiolitis, showing that tracheobronchial aspirates may be a useful diagnostic tool for identifying unseen respiratory issues.