Kristiina Ruotsalo 

Animal Health Laboratory, University of Guelph, Guelph, ON. 

AHL Newsletter 2020;24(2):20. 

A 10-year-old Hanoverian mare presented with a clinical history of chronic sinusitis with right-sided nasal discharge. Endoscopy revealed plaques of purulent material, and samples from the right frontal sinus were submitted for cytological examination and bacterial culture. 

The cytological preparations contained hemorrhagic backgrounds with large numbers of markedly lytic neutrophils. Numerous extracellular bacteria composed of both small cocci and variably sized rod-shaped organisms were noted. Large numbers of extracellular, small, round, slightly refractive structures consistent with conidia were found throughout the slides as well as in clusters in association with stalks, or condiophores (Fig. 1). Also present were numerous septate, non-pigmented fungal hyphae which were intermixed with inflammatory cells (Fig. 2).  

Culture revealed growth of a mixed bacterial population along with 4+ growth of fungus consistent with Aspergillus spp.; fungal speciation was not requested. 

Aspergillus species are saprophytes that are widely distributed in the environment, being found in soil, decaying vegetation, and organic debris. These organisms are opportunistic, and healthy animals are typically resistant to infection unless exposed to massive numbers of conidia or mycelia. Transmission is usually by aerosol. Conidia can remain in suspension in air for a long time due to their small size and hydrophobicity and are ubiquitous in the environment of horses. Typically, mucociliary clearance and phagocytosis by macrophages are effective in clearing inhaled organisms. The risk of infection may be increased in the presence of severe concurrent illness, or with immunodeficiency. This mare did not have any reported evidence of illness or other predisposing factors, and unfortunately was lost to follow up, so response to therapy cannot be reported.  

Because of the universal exposure of horses to Aspergillus and other fungi, it is important to demonstrate the presence of conidia or hyphae within diseased tissue. This may be done via cytological evaluation of affected tissue or exudates, or biopsy of affected tissues, along with culture of that material. Aspergillus grows well on most fungal culture media.   AHL