Equine respiratory viruses, airway inflammation and performance in thoroughbred racehorses.

This study examines whether respiratory viruses are associated with equine asthma, a common contributor to poor racing performance in Thoroughbred horses. The researchers found that although certain viruses were commonly detected in the animals’ upper airways, their presence did not directly relate to clinical signs of the condition nor affect the horses’ racing performance.

Understanding the Research Study

This research aimed to determine the role of respiratory viruses in the manifestation of equine asthma and their impact on the performance of racehorses. For this purpose, the researchers examined different variables, such as:

• The presence and abundance of equine herpesviruses (EHV-1, 2, 4, 5) and equine rhinitis A and B viruses (ERBV, ERAV) in the nasopharyngeal, tracheal, and bronchoalveolar lavage fluid (BALF) samples from the horses.
• The association between viral detection and load and clinical signs, performance, BALF cytology (study of cells), and exposure to the environment.

Main Findings

The study had key findings such as:

• EHV-1 and ERAV were not detected in any of the samples, while EHV-4 was found only in one sample.
• EHV-2, EHV-5, and ERBV had higher probabilities of being present in the upper airway samples than in BALF samples.
• The detection or abundance of respiratory viruses did not correspond with clinical symptoms or impacts on performance.
• The presence and abundance of ERBV in the nasopharynx and EHV-5 in the trachea were connected with a higher proportion of neutrophils (a type of immune cell) in BALF. However, having a high load of EHV-5 in the nasopharynx was not linked with this.
• The detection and load of EHV-2 in the nasopharynx were related to a decrease in mast cells in BALF.
• Horses that had respirable dust exposures had a higher likelihood of ERBV detection.

Conclusion

The researchers conclude that these specific viruses are often present in the upper airways of healthy racehorses. However, their direct role in the onset of equine asthma still remains unclear. As there was no direct link found to clinical signs or performance deficits, further research is required to establish a concrete relationship between these respiratory viruses and equine asthma.