Conference Agenda

Transmission is a basic aspect of intestinal parasite’s biology that is poorly understood for Dientamoeba fragilis. Early historical reports reflecting the absence of a cyst are often cited as a central argument in debates supporting the lack of a D. fragilis cyst. Despite D. fragilis cysts being described since Dobell’s original description, their existence is not universally accepted. Here, Dobell’s, Wenyon’s, and Hoare’s collection of historical faecal smears stored at the Natural History Museum (London), dating back to the 1890s and the early 1900s, were examined for forms consistent with modern descriptions of D. fragilis cysts, and an example was found in one slide. Such rare forms were also detected during examination of stained faecal smears archived in the parasite reference laboratory collection at the United States Centers for Disease Control and Prevention (CDC). Considering published literature on the subject of D. fragilis cysts and the broader picture of cyst formation across diverse members of Parabasalia, we recommended that future investigations on D. fragilis transmission consider mounting evidence for the role of a true cyst despite its rarity in human faecal specimens. The factors leading to cyst formation and further characteristics of this life cycle stage require further study.