Oral Candidiasis, Candidiasis that develops in the mouth or throat. Thrush of the mouth, more commonly called oral thrush, is an overgrowth of the Candida Albicans fungus, a yeast-like organism that naturally lives in people's intestines, skins and mouths. Esophageal thrush is a painful yeast infection of your throat, also known as esophageal candidiasis. If left untreated, it can spread and become a severe condition.