Analytical methods of fungal detection
In order to refine clinical interpretation, potential cytological markers have been investigated in our study, such as identification of type of fungal elements (spores or hyphae) and whether they were phagocytosed or not. As spores represent a dormancy form and hyphae a growing form of fungi, the latter have previously been evaluated in the context of MA.10 Our results showed that identification of growth as well as phagocytosis of fungal elements is not significantly correlated with either clinical signs, inflammation or diagnosis of equine asthma; thus precluding the use of these as biological markers of occurrence or severity of asthma in horses.
A high prevalence of fungal detection by cytology in TW of non-asthmatic horses has been reported previously,10,21,22 and also confirmed in the current study. Moreover, the prevalence of fungal detection by cytology in BALF of CTL and MA horses drives to the conclusion that this method is not relevant for the investigation of fungi elements in athletic horses. Indeed, horses with a positive cytology in TW or BALF were less likely to exhibit cough, because of the very large proportions of fungi detected by this method among control horses with no clinical signs. However, the results of the current study did identify a significant association between fungal detection by cytology in BALF and SA. Severe asthmatic horses were indeed prone to exhibit fewer fungal elements compared to moderate asthmatics. This finding concurs with a previous study in which intracellular fungal-like particles were less commonly observed in the macrophages of severe asthmatic horses exposed to hay, compared to healthy horses.23 The authors suggested that fungal particles were trapped more proximally in the respiratory tract, due to increased mucus and bronchoconstriction. An alternative hypothesis would be a decreased phagocytic capacity of macrophages of horses with SA, as previously demonstrated ex vivo .24