Equine pythiosis in Egypt: clinicopathological findings, detection, identification and genotyping of Pythium insidiosum

Abstract

Background Equine pythiosis is an emerging, devastating disease that is hard to treat. The tumour‐like nodular skin masses grow rapidly and the outcome is generally fatal, and thus early diagnosis and intervention are important. Objectives (i) To highlight the clinical, histological and haematological findings in pythiosis, and (ii) to evaluate the efficacy of direct sample multiplex‐PCR targeting the single nucleotide polymorphisms within the ribosomal DNA region for detection and genotyping of Pythium insidiosum. Animals Two hundred and twenty horses including 204 Arabian and 16 draft horses were surveyed. Methods Case series study diagnosis was based on clinical, pathological and haematological findings typical of P. insidiosum infection, culture identification, immunohistochemical investigation and direct sample PCR. Results The affected horses (24 of 220, 10.91%) presented with unifocal or multiple lesions on the abdomen, limbs, chest, face and mammary gland. Cases commonly had a history of access to stagnant water, ponds and intentionally flooded rice fields. Most were pregnant mares (58.33%). Histopathology revealed granulomatous reaction, blood vessel endotheliosis, heavy infiltration of eosinophils in the dermal layer, multifocal necrosis and Splendore–Hoeppli phenomenon. Unlike direct microscopy (50%) and culture (91.6%), multiplex‐PCR assay identified P. insidiosum (Clade II) in all tested samples. To the best of the authors knowledge, this is the first study determining a clade of P. insidiosum causing equine pythiosis in Egypt. Conclusions and clinical importance Direct sample multiplex‐PCR assay is a potential tool for the early and rapid diagnosis of equine pythiosis. It overcomes limitations associated with morphological identification and provides a definitive diagnosis.