Seasonal airborne fungal emissions from a horse stable as a localised source of environmental exposure

Abstract

Airborne fungal contamination in equine facilities remains insufficiently understood despite their high organic matter load and seasonally restricted ventilation. This study examined the seasonal variability, species composition, and environmental relevance of culturable airborne fungi in a traditional English-style horse stable, with particular emphasis on the genus Aspergillus. A total of 180 indoor and 60 outdoor air samples were collected in autumn, winter, and spring via an MAS-100 impactor and three culture media (SAB, MEA, DG18). Fungal concentrations showed pronounced seasonality, with winter displaying the highest levels (up to 5,110 CFU/m³ indoors and 32,170 CFU/m³ outdoors on DG18), whereas spring presented the lowest values (921–1631 CFU/m³). The autumn concentrations were intermediate. Significant medium-dependent differences occurred only in spring (Friedman, p = 0.0038), where SAB produced the lowest counts. No significant correlations were found between total fungal concentrations and temperature or humidity across media and sample types, except for a strong positive correlation with temperature and a moderate negative correlation with humidity in winter (examined samples on MEA), and a very strong negative correlation with humidity in spring (control samples on SAB). Aspergillus spp. dominated across all the seasons, with A. versicolor (25%), A. amoenus (18.8%), and A. fumigatus (15.6%) forming the core mycobiota. The winter outdoor controls presented unexpectedly high fungal loads, indicating restricted atmospheric dispersion and supporting the role of the stable as a seasonal localised point source of airborne fungal aerosols. The persistent presence of allergenic and opportunistic pathogenic species such as Aspergillus fumigatus highlights shared exposure risks for horses, stable workers, and nearby populations. These findings demonstrate that equine stables represent overlooked contributors to local bioaerosol loads and underscore the need for routine monitoring within a One Health framework.