# Genomic Epidemiology of Fungi Identified in Bronchoalveolar Lavage Fluid from Asthmatic Horses in the US

## TL;DR

This study explores how fungi in the airways of asthmatic horses vary by region and how this affects the type of inflammation they experience.

## Contribution

The study identifies geographic variations in fungal exposure and their association with specific inflammatory responses in asthmatic horses.

## Key findings

- Fungal community composition and inflammatory cell proportions in horse airways vary significantly by ecoregion.
- Alternaria, Aspergillus, Cladosporium, and Epicoccum species show differing abundances across regions.
- Geographic differences in fungal exposure may explain regional variations in asthma inflammation types.

## Abstract

Asthma is a common cause of respiratory disease and poor performance in horses and can range in severity from occasional coughing and decreased athletic performance to difficulty breathing at rest. Along with variations in severity, different types of inflammation can occur in the lungs of horses with asthma. Fungal exposure, often from moldy hay, has long been known to trigger disease in horses; however, it is not known if exposure to specific types of fungi plays a role in determining the type and severity of disease. Little is known about the variation in airborne fungi encountered by horses in different geographic regions. Analysis of the fungal DNA present within the airways of horses with asthma living in different regions can identify the types of fungi that they are exposed to. In turn, comparisons of the different fungi present in different regions can be made. In addition, this information can help determine which fungi are associated with the various types of asthma in horses. This knowledge can improve asthma prevention and management, provide new targets for research and expand our understanding of the disease processes that lead to asthma in horses.

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.