A Mexican Honeymoon Marred by Gastrointestinal Upset: A Case of Dientamoeba fragilis Causing Post-infectious Irritable Bowel Syndrome

Dientamoeba fragilis (D. fragilis) is an anaerobic intestinal protozoan parasite that has been associated with irritable bowel syndrome (IBS)-like symptoms. We report a case of post-infectious IBS caused by D. fragilis treated successfully with metronidazole. A 33-year-old African American male with an unremarkable past medical history was seen in the office with a three-month history of intermittent, generalized, crampy abdominal pain with bloating and flatulence without associated weight loss. He visited Mexico for his honeymoon four months ago. Initial lab work was normal. Dietary changes including fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet and loperamide were prescribed with the presumptive diagnosis of IBS; however, his symptoms persisted. Three samples of stool for ova and parasites (O&P) were positive for D. fragilis. The patient was treated with metronidazole for 14 days. Repeat fecal O&P were negative. Upon follow-up, the patient’ symptoms substantially improved with a resolution of abdominal pain and flatulence. Infection caused by D. fragilis may be symptomatic or asymptomatic. It is transmitted by the fecal-oral route. Symptoms include abdominal pain, bloating, and alteration of bowel movements, resembling IBS. The diagnosis is made via the detection of D. fragilis trophozoites in appropriately fixed and stained stool samples or by a polymerase chain reaction. Treatment options include tetracyclines, paromomycin, metronidazole, and Iodoquinol. Further epidemiologic studies may help in elucidating the association between D. fragilis and IBS.