Disease / Pathogenesis
The flagellate infects the mucosal crypts of the large intestine which are located close to the mucosal epithelium cells. The organism is not considered to be invasive or produce any type of cellular damage. However it does cause surface irritation that initiates an eosinophilic inflammatory response. Symptoms vary but commonly include abdominal pain and variable diarrhea. Stool appearance can be greenish-brown, mucoid, but not usually bloody. Disease is produced regardless of the host’s immune status.
Most common in children ages 5-10 years. Other symptoms that patients may have include flatulence, bloating, constipation, anorexia including weight loss. Less common symptoms may include irritability, pruritus, headache and fever. These symptoms may be the result of co-infections with helminths.
Location in Host
The location of the parasite is the large intestine (cecum and illeum)
Cosmopolitan in distribution
There is no definitive vector however other helminths are thought to be mechanical vectors of the flagellate to the host. An example is Enterobius vermicularis or pinworm. This is due to Dientamoeba fragilis having no known cyst form which would more efficiently act as a transmissible form. Only the trophozoite form of the flagellate can be detected in ova and parasite examinations. Hand/mouth transmission is also thought to be a viable mode though limited by the frailty of the trophozoite.
Morphology & Diagnosis
The organism as noted previously does not have a known cyst stage. The diagnostic stage is the trophozoite stage which is characteristically binucleated and stains lightly. The light staining may make it difficult for the inexperienced to detect it in stained preparations as the trophozoite may blend in with background material. The size of the trophozoite is approximately 5 to 15 um which is particularly small and therefore makes it even more difficult to detect.