Standardization of Diagnostic Criteria for Eosinophilic Chronic Rhinosinusitis in the Oestrus Ovis Infected Sheep Model

Abstract

Background The sheep is an established model for endoscopic surgical procedures, as well as for postsurgical healing. Standardization of the presence and the degree of eosinophilia within this model still has not been done. This study was undertaken to show the eosinophilic response secondary to Oestrus ovis parasitic infestation within the nasal cavity to standardize the sheep model of chronic rhinosinusitis (CRS) and to set diagnostic criteria for CRS in sheep. Methods Nasal mucosal secretions were obtained from sheep naturally infested with O. ovis and showed signs of CRS and from sheep treated with ivermectin to prevent the infestation. Full thickness mucosal biopsy specimens from the lateral nasal wall were obtained also from these sheep. After histological fixing and staining, the degree of eosinophilia in the mucous secretion smears and in the epithelial layer of the lateral nasal wall was quantified using a light microscope. Results The average number of eosinophils in the mucous secretions and in the nasal wall epithelium was significantly higher in the sheep that showed signs of rhinosinusitis and had visible O. ovis larvae compared with control sheep (p = 0.003 and p = 0.05, respectively). Conclusion Based on the average numbers of eosinophils observed the diagnostic criterion for CRS in sheep is two eosinophils per high-power field averaged over three fields of secreted mucous smears or an average of at least one eosinophil per high-power field of nasal wall epithelial biopsy specimens.