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