Pythium insidiosum is the causative agent of "swamp cancer" especially in horses, mainly in wet tropical environments.
Infections are characterised by tumour-like masses which develop mostly on the legs. Lesions eventually ulcerate and produce draining sinuses. Bone may also become involved. Infections have also been reported in cats and dogs and rarely in humans.
Cultures are white to cream, flat often with submerged growth. Microscopically, hyphae are sparsely septate, 4-6 um wide with irregular branches.
de Hoog et al. (2000, 2015).