Equine asthma: Integrative biologic relevance of a recently proposed nomenclature

Abstract

The term “equine asthma” has been proposed as a unifying descriptor of inflammatory airway disease (IAD), recurrent airway obstruction (RAO), and summer pasture‐associated obstructive airway disease. Whilst the term will increase comprehensibility for both the lay and scientific communities, its biologic relevance must be compared and contrasted to asthma in human medicine, recognizing the limited availability of peer‐reviewed equine‐derived data, which are largely restricted to clinical signs, measures of airway obstruction and inflammation and response to therapy. Such limitations constrain meaningful comparisons with human asthma phenotypes. Suggested minimum inclusion criteria supporting the term asthma, as well as similarities and differences between IAD, RAO, and multiple human asthma phenotypes are discussed. Furthermore, differences between phenotype and severity are described, and typical features for equine asthma subcategories are proposed. Based on shared features, we conclude that mild/moderate (IAD) and severe (RAO) equine asthma are biologically appropriate models for both allergic and non‐allergic human asthma, with RAO (severe equine asthma) also being an appropriate model for late‐onset asthma. With the development of new biologic treatments in humans and the application of more targeted therapeutic approaches in the horse, it would appear appropriate to further investigate the allergic (Th‐2) and non‐allergic (non‐Th‐2) phenotypes of equine asthma. Further research is required to more fully determine the potential clinical utility of phenotype classification.

Clinical features and radiographic findings in cats with eosinophilic, neutrophilic, and mixed airway inflammation (2011‐2018)

“…This tendency toward a younger age of onset parallels the development of asthma in humans, most commonly a childhood disease where the allergic or hypersensitivity response is related to specific development of neonatal and juvenile immunity 21‐23 . In neonatal murine models of asthma, increased diversity of lung or gut microbiota promotes a more favorable environment for tolerance against allergic disease by inducing T‐regulatory cells, lower concentrations of IgE and altered balance of Th1/Th2 immune responses 24‐26 . In studies of cats, a similar relationship has been suggested between gut and lung mucosal microbiomes 27,28 .…”

Fecal microbiota in horses with asthma

“…Asthma in horses is characterized by reversible bronchospasm and airway inflammation upon exposure to inhaled antigens. It is a complex disease that includes individual susceptibility to allergen exposure, variable levels of severity, and different inflammatory phenotypes . Exacerbations are characterized by the presence of clinical signs and are mainly triggered by exposure to aerosolized allergens found in hay and bedding, including fungal particles, mites, and endotoxin .…”

Effects of nebulized dexamethasone on the respiratory microbiota and mycobiota and relative equine herpesvirus‐1, 2, 4, 5 in an equine model of asthma

“…Mild asthma in horses is a commonly occurring inflammatory airway disease, which provides a biologically appropriate model for allergic and nonallergic phenotypes of asthma in humans . It is a naturally occurring disease that, similar to asthma in humans, likely is triggered by a combination of pathophysiological mechanisms.…”