Clinical-pathological, immunohistochemical, ultrasonographic, and Doppler flowmetry evaluation of intestinal pythiosis in a dog

Resumo

Background: Pythiosis is a chronic pyogranulomatous infection of the gastrointestinal tract caused by the oomycete of the genus Pythium, which inhabits soil and aquatic environments. This disease has a global distribution, predominantly affecting horses, canines, and humans. In dogs, the gastrointestinal form is more prevalent than the cutaneous form. Pythiosis leads to thickening of the gastrointestinal wall and obliteration of its layers. Histopathologically, it is characterized by a pyogranulomatous inflammatory reaction with a marked eosinophilic component. Diagnosis can be confirmed through immunohistochemistry or other techniques, such as isolation and molecular evaluation. This study aims to report a case of canine gastrointestinal pythiosis, detailing the clinical, ultrasonographic, histopathological, and immunohistochemical findings.

Case: A 3-year-old male Pointer dog was presented to the Veterinary Hospital at the Federal University of Paraíba, Areia, Brazil, with a one-month history of anorexia, vomiting, and progressive weight loss. On physical examination, a mass was palpated in the medial portion of the abdomen. Ultrasonography revealed thickening of the gastrointestinal wall, with areas showing both normal and obliterated layers. Vascularization was observed within the thickened wall via Color Doppler. Based on these findings, the dog underwent an exploratory celiotomy. Due to the extensive nature of the lesions and an unfavorable prognosis, euthanasia was performed. Macroscopic evaluation revealed wall thickening from the distal duodenum to the middle third of the jejunum, along with obliteration of the jejunal lumen layers and the presence of a large serosal mass (8 cm). Cytology demonstrated rare, uniform, linear, elongated, branched, and poorly septated hyphae within a pyogranulomatous and eosinophilic inflammatory reaction. Tissue samples were fixed in 10% formalin, routinely processed, embedded in paraffin, and stained with hematoxylin and eosin. Histopathological examination revealed multinucleated giant cells, macrophages, neutrophils, and numerous eosinophils extending from the mucosa to the serosa. Hyphae were observed in some areas, surrounded by eosinophilic and pyogranulomatous inflammation. Grocott methenamine silver staining showed positivity for branched and irregularly septated hyphae. In the immunohistochemical evaluation, positive staining confirmed the diagnosis of Pythium insidiosum infection.

Discussion: Gastrointestinal pythiosis typically presents with nonspecific clinical signs and should be considered a differential diagnosis in adult dogs with gastrointestinal disorders. This disease occurs in a significant percentage of canines in suburban areas, often without documented exposure to environments with water accumulation and high temperatures, as described in this case. The diagnosis of intestinal pythiosis in this report was based on a combination of clinical, epidemiological, ultrasonographic, microbiological, histopathological, and immunohistochemical findings. This case exhibited characteristics consistent with previous reports, but notably, the gastric wall was not involved. Due to the extensive lesions extending from the end of the duodenum to the middle third of the jejunum and the poor prognosis, euthanasia was elected. Consequently, the treatment typically recommended in the literature, which includes surgical resection combined with postoperative antifungal therapy, was not pursued.