Equine asthma - old disease and new concepts.

Equine asthma is increasingly recognised as a biologically heterogeneous syndrome in which similar clinical manifestations may arise from distinct molecular mechanisms. Although clinical phenotypes have substantially improved disease classification, increasing evidence indicates that molecular endotypes more accurately reflect the biological mechanisms underlying disease heterogeneity. This review summarises current knowledge regarding the pathophysiological mechanisms of equine asthma, with particular emphasis on inflammatory pathways, molecular endotypes, genetic susceptibility, airway remodelling and emerging neuroimmune interactions. Special attention is given to the transition from phenotype-based disease classification towards mechanism-based endotyping and its potential implications for future diagnostics and targeted therapeutic strategies. The review was based on a comprehensive search of the PubMed and Scopus databases using the terms "equine asthma", "diagnostics", "phenotypes", "endotypes", "genetic background" and "neuroimmune pathophysiology". Following predefined selection criteria, 146 publications were included in the review. Current evidence demonstrates that persistent airway inflammation, structural remodelling, genetic background and neuroimmune signalling interact throughout disease progression and cannot be fully explained by clinical phenotypes alone. Improving our understanding of these biological mechanisms will facilitate more precise disease classification and may provide the foundation for future biomarker-guided diagnosis and precision medicine in equine asthma.