Pythiosis is a potentially fatal infectious disease of animals and humans caused by Pythium insidiosum throughout the world. Pythium insidiosum is a fungus-like peronosporomycete (Oomycete) aquatic organism belonging to the kingdom Stramenopila phylum Oomycota, and order Pythiales (family Pythiaceae). It is believed that biflagellate mobile zoospores, which are the infective forms of P. insidiosum present in water, enter the body through skin injuries¹.

Among all reported pythiosis cases, the frequently affected hosts included horses followed by humans, dogs, cows, sheep, and cats. The infection is not contagious; no animal-animal or animal-human transmission has been reported so far¹. Cases have also been reported in donkeys, mules, camels, bears, birds, goat, tiger, and jaguar. In animals, the disease has been mainly reported from the USA, Brazil, Australia, Colombia, Egypt, Venezuela, and Costa Rica. In India, the condition has been recorded in horses, shrimps and humans^2-4. In sheep, the disease has been described in three forms, namely cutaneous, rhinofacial and digestive. Among them, the cutaneous and rhinofacial forms have been reported to cause 100% mortality and severe economic loss for the farmers⁵. Considering the importance of the disease and lack of reports of pythiosis in India, the present communication describes pathological features of ovine rhino facial pythiosis recorded in the clinical case.

A two-year-old non-descriptive ewe from a flock of twelve sheep, raised extensively was presented to the Veterinary Clinical Complex, Rajiv Gandhi Institute of Veterinary Education and Research, Puducherry, India with the history of slowly progressing unilateral swelling in the nasal cavity, nasal discharge and dyspnoea. After clinical examination, incisional biopsy was performed under local anaesthesia and tissue samples were collected. The tissues were fixed in 10% neutral buffered formalin, processed by routine paraffin embedding technique and 4-5 pm sections were stained with Haematoxylin and Eosin stain. Serial sections were stained by Gomori methenamine silver and Periodic acid Schiff as described previously⁶.

Clinical examination revealed unilateral serosanguinous discharge and cauliflower-like growth protruding from the left nostril which was attached to the maxillary bone almost occluding the nasal passage (Figs. 1 and 2). Gross lesion of the present case was similar to those described in Sheep from Brazil⁹and Texas, USA⁹, wherein facial deformity with intranasal growth partially occluding the nasal passage along with necrosis involving the nasal septum were also recorded. Ovine rhinofacial pythiosis, also known as “bull nose” is characterized by necrotizing rhinitis with marked enlargement and deformity of the nasal region, severe respiratory difficulty and bloody nasal discharge⁹.

Histopathological examination revealed intact ciliated columnar epithelium with focal hyperplastic reaction (Fig. 3). The sub-mucosa revealed the presence of amorphous myxoid and rarefying osteitis amidst loose fibrous tissue proliferation (Fig. 4). Further, characteristic pyogranulomas with central amorphous eosinophilic area, surrounded by neutrophils, eosinophils, karyorrhectic debris (Splendore-Hoeppli reaction) were observed (Figs. 5 and 6). The microscopic features observed concurred with the reports of earlier workers^7,8,10. P. insidiosum triggers in the infected host a T helper 2 [Th2] subset response with an inflammatory reaction composed mainly of eosinophils and mast cells. These cells degranulate around the hyphal elements of P. insidiosum leading to a Splendore-Hoeppli-like reaction¹¹.

In the present case, Periodic acid - Schiff staining failed to demonstrate the presence of fungal elements which could be due to the fact that PAS does not stain dead hyphae within the necrotic tissue (Splendore-Hoeppli material) or due to the lack of chitin, an aminopolysaccharide present in the cell wall of the fungus that is absent in P. insidiosum. However, Grocott methenamine silver staining revealed black coloured, thin-walled, non-parallel and sparsely-septate hyphae with dilatations (Fig. 7) and is similar to the findings of previous study⁹.

Earlier studies have highlighted the involvement of other organs like lymph nodes and lungs in sheep through metastases⁵, ¹² which were not recorded in the present study. Diagnosis of pythiosis can be made based on clinical signs as well as gross and microscopic lesions. Differential diagnosis however, in rhinofacial pythiosis be made from conidiobolomycosis that usually involves the rhinopharyngeal area¹⁰.

The present case report describes rhino facial pyth-iosis in a sheep based on histopathology and histochemistry. The prognosis is poor if the disease is chronic and complete surgical excision is not possible. Although the incidence of the disease is low in sheep in India, an early diagnosis may help in evolving a control strategy.

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