Prevalence of fungal detection
A large number of fungal genera were identified in this study, with Aspergillus sp. and Penicillium being the most commonly found in respiratory fluids. While similar genera have been reported in previous studies,10,25 up to 5 different genera or up to 5 different species ofAspergillus sp. could be concomitantly identified in the airways of a single horse. It has previously been documented thatPenicillium , Aspergillus sp., and Muroraceaegenera were airborne, ubiquitous and frequently found in the air of stables26 while Aspergillus sp. is the most commonly isolated fungi in hay.12,27 Detection of these fungal elements in the airways may simply reflect the environment in which the horse was located before and during sample collection.10,21,28 Indeed, the authors of a recent publication identified the fungal microbiota present along the upper and lower respiratory tract of healthy horses, and showed that fungal microbiota of the pharynx was similar to that of the trachea in healthy horses, indicating that the pharynx is potentially a major source of microbes that translocate to the lower respiratory tract.25 Even though an association between fungal content in hay samples and fungal elements in the airways of horses has not been identified,12 other sources of contamination in horses’ stables remain to be investigated.
In the current study, the genus Aureobasidium sp. was found in BALF only (and not in TW) of 10 horses (9 MA, 1 CTL). In horses, few anecdotal studies reported the detection of Aureobasidium sp. in fungal microbiota of the conjunctiva of clinically healthy horses,29 in paranasal sinus of healthy and diseased horses30 and through ITS2 gene sequencing (mycobiota) in BALF of horses.31 However, the existence of an immune-mediated hypersensitivity reaction leading to interstitial pneumonitis due to Aureobasidium pullulans has been reported in the human literature.32 Further studies are required to confirm the possible pathogenicity of Aureobasidium sp. and determine whether specific genera would present more risk than others for the development of equine asthma.