EXPLORING EQUINE ASTHMA: PATHOGENESIS INSIGHTS AND DIAGNOSTIC CHALLENGES

Equine asthma (EA) is a common respiratory syndrome of horses, including a spectrum of chronic inflammatory disorders of the lower airway, which can be classified as mild-moderate (MEA) or severe (SEA), based on clinical severity. Although it is spread worldwide and has been studied for decades, gaps persist in our understanding of EA's pathogenesis. This highlights the need for refined diagnostic procedures to swiftly identify and subcategorize EA, finally enabling targeted therapeutic interventions. This doctoral thesis attempted to fill these gaps through a series of retrospective and prospective studies, aiming to contribute to the EA scientific community with valuable insights. Notably, our findings based on intradermal testing revealed that SEA-affected horses predominantly exhibit late-phase type I hypersensitivity, whereas MEA-affected horses manifest type IV hypersensitivity. Furthermore, our investigations demonstrated associations between distinct immune response types and various EA severity and cytological subtypes, including innate immunity, Th2, and Th17 responses. In addition to intradermal testing, thoracic ultrasonography showed promise as a diagnostic tool for EA. Indeed, ultrasound alterations were more prevalent in SEA-affected horses than those with MEA, correlating with increased neutrophils in bronchoalveolar lavage fluid. In racehorses, while EA did not appear to be linked with dynamic upper airway obstructions, it did show an association with impaired athletic capacity in cases of neutrophilic inflammation. Oscillometry studies proved to be encouraging, revealing differences in respiratory reactance between healthy and MEA-affected horses in a mixed population. Conversely, among racehorses in training, no differences in lung function were observed at rest, but horses with MEA experienced increased resistance after intense exercise compared to their healthy counterparts. In summary, our results contribute to the understanding of key aspects of EA etiopathogenesis, laying the foundations for future research. Additionally, we advocate for the inclusion of intradermal testing and thoracic ultrasonography in a comprehensive diagnostic protocol for EA. Finally, our innovative work with oscillometry underscores its diagnostic potential, opening doors to various fields of application in equine respiratory medicine.