Fatal vascular pythiosis in a dog from Thailand: Clinical presentation and pathological findings—first report: A case report

Abstract

Vascular involvement in Pythium insidiosum infection is exceedingly rare in dogs and often results in delayed diagnosis due to nonspecific clinical signs. A one-year-old female German Shepherd presented with subcutaneous edema and mass-like lesions on the right hindlimb, caudal abdomen, and tail base. Computed tomography lymphangiography revealed lymphedema with impaired lymphatic drainage, and cytologic evaluation demonstrated pyogranulomatous inflammation, including multinucleated giant cells containing poorly stained, contorted fungal hyphae within the cytoplasm. Despite right hindlimb amputation, the disease progressed to ischemic necrosis, gangrene and eventual autoamputation of the left hindlimb and tail. Severe P. insidiosum infection was confirmed by histopathologic examination and immunochromatographic testing. Clinical deterioration continued despite aggressive antifungal and antimicrobial therapy, leading to euthanasia. Postmortem examination revealed extensive pyogranulomatous and necrotizing inflammation involving the aorta, caudal vena cava, kidneys, uterus and intestines. Broad, ribbon-like, sparsely septate hyphae were observed and confirmed as P. insidiosum by culture, and by Internal Transcribed Spacer Polymerase Chain Reaction. This case represents the first reported instance of vascular pythiosis in a dog, highlighting its rarity, severity and poor prognosis. Early recognition of vascular involvement is critical, as delayed diagnosis and limited therapeutic response are frequently fatal.