LIMITATIONS
Fungal detection in BALF was performed on pooled BALF only, and not on individual right and left BALF, which could have led to an overall lower prevalence of fungal detection by culture in BALF. In a previous study, while 100% of horses with “positive” pooled BALF were also positive in left and/or right BALF, 14.6% of horses with “negative” pooled BALF were positive in left and/or right BALF.12
Beyond detection of fungi in TW or BALF, quantification of the fungal load in the airways also needs to be further investigated. Cytological investigations of fungal elements were limited to qualitative dichotomy (presence or absence) only. Quantification of fungal-like intracellular particles by cytology or total fungal load quantification by qPCR assay (18S rRNA gene) have recently been proposed, but these methods are yet to be validated.23 Absolute quantification by successive dilutions (as performed for bacteria in TW for instance)16 were laborious, unrepeatable (data not shown) and ultimately unsuccessful for fungal cultures. However, establishment of a “pathological” cut-off, possibly through molecular biology, could however help in the future for differentiating true fungal infection from environmental contamination.
This study focused on fungi detection in airways samples, while ambient airborne samples or component of horses’ environment (bedding, food) were not collected. No association between fungal content in hay samples and fungal elements in the airways of horses was detected in a previous study.12 It would however have been interesting to collect respirable and inhaled particulate samples in the horse’s breathing zone, as previously described.47,48 The relevance of such sampling, factually excluding horses referred to the hospital for consultation, is however limited to field studies only, most frequently focusing on MA rather than SA.