Abstract
Ambient pollution is associated with the development and exacerbation of human asthma, but whether air pollution exposure is associated with lower airway inflammation in horses has not been fully evaluated. The Air Quality Health Index (AQHI) is an online tool used by asthmatic Ontarians to modify their outdoor activity when ambient pollution is high. A single AQHI value, falling on a scale from 1 to 10+, is calculated from measurements of fine particulate matter (PM2.5), nitrogen dioxide (NO2), and ozone (O3). Increased AQHI values predict an increased risk for presenting to a health care provider for assessment of asthma exacerbation, with a time lag of 0–9 days after an increase. Whether ambient air pollution is a risk factor for identifying increased lower airway inflammatory cells on cytologic evaluation of bronchoalveolar lavage fluid (BALF) of horses has not yet been explored. To investigate this relationship, case data including BALF cytology preparations from horses across southern Ontario, Canada, were retrieved from the Guelph Animal Health Laboratory's archives. Spanning the years 2007–2017, 154 cases were identified within a 41- by 30-km area surrounding the cities of Guelph and Kitchener. In 78 of 154 cases, cytologic reevaluation identified increased proportions of one or a combination of BALF neutrophils (mean 5%, range 0–15%), eosinophils (mean 2%, range 0–31%), and mast cells (mean 4%, range 0–10%). To assess the effect of lagged pollutant and temperature exposures in these 78 cases, weekly mean values of AQHI, PM2.5, NO2, O3, and temperature were recorded for the 4 weeks prior to the date of the horse's presentation for respiratory tract evaluation. The relationship between ambient exposures and increased proportions of lower airway granulocytes was evaluated using a case-crossover design. Single unit increases in 2-, and 3-week lagged weekly mean PM2.5 and NO2, were associated, respectively, with an 11% (p = 0.04, 95% confidence interval, CI = 1.01–1.22), and 24% (p = 0.03, 95% CI = 1.08–1.43) greater risk of identifying increased lower airway granulocytes. These findings suggest that exposure to increased ambient pollutants is associated with lower airway inflammation in Guelph and Kitchener area horses.
Highlights
Inflammatory airway disease (IAD) is a common, performancelimiting, non-infectious disorder of the lower airways that can affect horses of any age, but is most commonly identified in younger sport horses [1,2,3,4,5]
Severe forms of human asthma can be associated with pulmonary blood vessel inflammation [18], but there is no record of an association between blood vessel inflammation and alveolar hemorrhage in humans
Increased mast cells accounted for the majority of cases with increased lower airway granulocytes
Summary
Inflammatory airway disease (IAD) is a common, performancelimiting, non-infectious disorder of the lower airways that can affect horses of any age, but is most commonly identified in younger sport horses [1,2,3,4,5]. IAD shares similarities with allergic and non-allergic human asthma [6] including airway hyperresponsiveness, intermittent cough, increased lower airway inflammatory cells, and differing responses to therapy based on the predominant inflammatory cell type [3, 6, 7]. Horses with IAD have increased proportions of lower airway granulocytes, including any one or a combination of neutrophils >5% but 1%, and mast cells >2% [3]. The subtypes that appear most similar to IAD are allergic asthma (>3% eosinophils), and the non-allergic forms of asthma including mixed granulocytic (>3% eosinophils) and paucigranulocytic [
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