Four species of flagellates that are commonly found in the intestinal tract are: Giardia duodenalis (also known is G. lamblia or G. intestinalis), Dientamoeba fragilis, Chilomastix mesnili, and Pentatrichomonas hominis. Other species exist, such as Enteromonas hominis, and Retortanmonas intestinalis, but are uncommon, rarely found, and are considered non-pathogenic. In this course, we will focus on the first four common species.
Among the first four listed, Giardia and Dientamoeba fragilis are considered pathogenic. This section of the course will therefore focus on these two organisms, as well as on ways to differentiate them from the non-pathogenic flagellates.
A few notes:
The species name attributed to Giardia varies according to source and time. It has been known as Giardia lamblia, G. duodenalis, and G. intestinalis. Many sources now just refer to it as "Giardia". The most commonly accepted species now is Giardia duodenalis, which is what we will use in this course.
Regarding Dientamoeba fragilis, it has been at times grouped with the amoeba (hence its' name) since it appears more amoeboid and it lacks external flagella. However, the CDC groups it with the flagellates.
