Anatomopathological and immunohistochemical study of pythiosis in naturally infected horse

The main goals of this study were to perform an anatomopathological evaluation of equine tissue naturally infected with Pythium insidiosus and to compare the reliability of Grocott methenamine silver nitrate (GMS) and the labeled streptavidin-biotin (LSAB) techniques for the diagnosis of pythiosis. Samples of cutaneous wounds suggestive of pythiosis obtained from 55 horses were histologically studied using hematoxylin-eosin and GMS stains, and LSAB. Twenty eight, out of 34 GMS-positive samples, were LSAB-positive for Pythium insidiosum. The six LSAB-negative samples were apparently cases of zygomicosis. The remaining samples were diagnosed as follow: granulation tissue with eosinophilic infiltration without necrotic areas (nine cases); granulation tissue with eosinophilic infiltration and necrotic areas (seven); habronemiasis (four); sarcoid (one). In conclusion, the LSAB method was more specific for the diagnosis of P. insidiosum. when compared to GMS.