Association of neutrophil morphology with bacterial isolates in equine tracheal wash samples.

This study investigates if the type of neutrophils found in horse tracheal washes is related to bacteria culture growth, noting potential variables such as age and time of year. Results suggest that the presence of certain types of neutrophils, particularly in younger horses, could indicate a bacterial cause for inflammation in the lower airways.

Research Objectives

• The goal of this research was to understand whether the types of neutrophils (nondegenerate or degenerate) found in horse tracheal washes would correlate with bacterial growth in the cultures. It aimed to identify whether this correlation is influenced by the horse’s age or seasonal factors.

Methods

• A cross-sectional study was conducted where tracheal wash samples from horses were gathered over a period from January 2013 to July 2015. All samples were evaluated based on set criteria.
• The research team analyzed any neutrophilia (an above-average number of neutrophils) and degenerate neutrophilia (a higher number of damaged or older neutrophils). These were rated on the Rossdales cytological scale.
• The neutrophil cicumstances in the samples were then related to potential bacterial pathogens related to respiratory diseases.
• The statistical analysis attempted to determine the link between the presence of neutrophilia vs its absence, and degenerate neutrophilia compared to non-degenerate neutrophilia. These analyses accounted for four independent variables.

Results

• Out of the 1100 horses with sufficient data, the researchers found that culture of potentially pathogenic bacteria was more likely in samples that contained degenerate neutrophils.
• The study also found that horses older than 9 years were less likely to have degenerate neutrophilia than horses aged 1-3 years old.
• Horses had a decreased chance of presenting degenerate neutrophilia during spring/summer compared to winter.

Conclusions

• The researchers suggest that neutrophil types in tracheal washes should be evaluated for bacterial inflammation, particularly in younger horses and during colder seasons.
• The study relied on routine lab submissions which might be a limitation due to lack of control over sample collection. Also, no submitted clinical history was taken under consideration.
• If degenerate neutrophils are not present, along with other factors, this could point at a non-bacterial cause for airway inflammation.