Abstract
Fungal exposure is strongly implicated in the pathogenesis of asthma in horses, but the importance of specific fungi is unknown. Geographic variation in equine asthmatic endotypes is suspected and might be related to different fungal exposures due to different climatological and geographical conditions. This study had two objectives: evaluate the effect of the ecoregion upon BALF inflammatory cells and fungal community composition in horses with asthma and evaluate the effect of BALF fungal community composition upon the likelihood of neutrophilic, mastocytic and eosinophilic inflammation in these horses. Differential cytology counts were obtained from 916 BALF samples submitted from horses with poor performance and/or clinical signs of respiratory disease from five ecoregions. The effect of the ecoregion upon BALF inflammatory cell proportions was modeled using generalized linear models. Seventy banked BALF samples were subjected to sequencing of the internal transcribed spacer regions of fungal DNA. Diversity analysis was performed in QIIME, including alpha diversity metrics and the Bray-Curtis dissimilarity metric. After taxonomy was assigned, differential abundances between ecoregions and inflammatory phenotypes were estimated by generalized linear models in DESeq2. BALF neutrophil (p < 0.0001) and eosinophil (p < 0.0001) proportions varied by ecoregion, while mast cell proportions did not (p = 0.18). Alternaria, Aspergillus, Cladosporium and Epicoccum spp. were found to differ in abundance between regions. These geographical variations in fungal exposure might be responsible for differences in BALF neutrophil and eosinophil proportions between ecoregions.