Association between fungal detection, airways inflammation and diagnosis of moderate to severe asthma in horses

Abstract

Background

Fungi are ubiquitous in horses' environment. Their contribution to the pathophysiology of severe asthma (SA) is acknowledged, while controversies remain for mild–moderate asthma (MA).

Objectives

We hypothesised that fungi are a risk factor for asthma. Our objective was to compare different combinations of analytical methods (cytology, culture) and sampling sites (tracheal wash (TW), bronchoalveolar lavage fluid (BALF)) in relation to clinical status (control, MA, SA).

Study design

Prospective cross-sectional study.

Methods

The study population included asymptomatic racing horses in the field and horses referred to the hospital for respiratory investigations. Fungi were detected by cytology and identified by mycology on TW and pooled BALF. Chi-square tests and multivariable logistic regressions were used for prevalence comparison between groups and association with clinical investigations.

Results

In total 155 horses (85 MA, 35 SA and 35 controls) were included in the study. The overall proportions of fungal detection in TW ranged from 45.7% to 89.4% among groups. The prevalence of fungal detection in BALF was significantly lower by cytology for SA (5.7%) than MA horses (23.6%) and significantly higher by culture for MA horses (31.8%) than controls (8.6%). Fungal detection by culture in BALF was significantly associated with high tracheal mucus score, high neutrophil proportions in BALF and diagnosis of MA.

Main limitations

Mycology was only performed in pooled BALF, and environment was not sampled.

Conclusions

Fungi were significantly more prevalent in the airways of MA horses than SA and/or controls. Fungal detection on TW, either by cytology or culture, was uninformative in a clinical context. Fungal detection by culture, but not cytology in BALF was associated with MA.