Equine asthma: An appropriate, translational and comprehendible terminology?

Abstract: In their editorial in Equine Veterinary Journal (EVJ) almost a quarter of a century ago, Hall and Stark [1] referred to the inability of clinicians, both human and veterinary, to separate and recognise the different clinical entities responsible for chronic diseases of the airways, with the subsequent development of several different approaches to terminology, as well as treatment. In relation to equine nonseptic lower airway disease, and despite many attempts to identify the most appropriate nomenclature, this challenge remains as topical today as it did then. ‘Equine asthma’ has recently been proposed as an appropriate term which recognises features both specific to, and shared between, diseases of the equine lower airways with the potential to clarify communication and reduce confusion [2]. The current edition contains 2 articles relating to nonseptic lower airway disease in the horse. The study by Bullone et al. [3] describes the association between disease severity and both environmental heat and airborne pollen concentration in a cohort of adult horses with both subjective (clinical score) and objective (pulmonary mechanics) evidence of increased respiratory effort at rest during stabling in a dusty environment. Readers will appreciate that the disease phenotype described is entirely consistent with the criteria used to define recurrent airway obstruction (RAO) (syn. Heaves) [4], yet will note the authors’ consistent use of the term ‘severe equine asthma’. In comparison, the study by Wichtel et al. [5] investigates the relationship between airway reactivity and indicators of airway inflammation in a cohort of predominantly young horses presenting with unexplained poor performance (not attributable to a nonrespiratory cause) and chronic cough. The exclusion criteria applied for study eligibility included evidence of laboured breathing at rest. Despite the reported discordance between evidence of airway inflammation and evidence of pulmonary dysfunction in a proportion of the horses studied, these specific criteria (lung function/airway hyper- responsiveness and BALF cytology) will be familiar to many readers as those principally applied in the diagnosis of inflammatory airway disease (IAD) [6]. In both ‘Introduction’ sections, each manuscript makes reference to the proposed aetiological role of aerosolised particulates in the respective diseases studied, a feature which, along with the other phenotypic similarities, questions the appropriateness of considering these conditions as entirely distinct from each other. Many readers will be aware of the gathering momentum towards a change in the overall terminology used to describe nonseptic lower airway inflammation in the horse [2,6]. This is largely borne out of an ever increasing awareness of a) the significant overlap between various inflammatory syndromes affecting the lower airways of horses and b) the diversity in clinical severity, aetiological triggers, molecular signatures and genetic predispositions associated with currently recognised specific syndromes. The extent of overlap and diversity becomes ever increasingly apparent year on year with the continued development and application of advanced clinical and research tools, ranging from basic respiratory cytology to immunological pathway discoveries and genetic profiling.