Dientamoeba fragilis (DF) is an intestinal protozoan originally seen in the early 1900ís. For some decades it was thought to be a harmless commensal, despite numerous published reports of illnesses associated with the infection Although its role as a pathogenic agent remains controversial, DF has been linked to chronic diarrhea, abdominal pain, nausea, anorexia and excessive flatulence. DF has also been implicated as a cause of colitis in adults. Allergic colitis with peripheral eosinophilia secondary to DF infection has also been described.
Colonization may occur without development of disease. In adults, asymptomatic colonization is present in 75-85% of individuals affected by the parasite. In children, the opposite is true; disease develops in as many as 90% of those colonized. No specific mortality is associated with this enteropathogen. Morbidity related to acute infection is in the first 1-2 weeks of the disease, with symptomatology predominated by diarrhea. Chronic infection occurs after 1-2 months of illness and is manifested by abdominal pain.
Much has been learned about the epidemiology of DF since its original description. By 1924, only 33 DF cases were recorded world-wide. Over the past four decades its global incidence has been studied varying considerably, generally being higher in immune compromised patients. The use of adequate culture techniques has increased detection of DF significantly with reported rates as high as 18% in Israel, 36% in Holland and 42% in Germany. Higher rates of infection are seen in crowded conditions with poor personal hygiene.
Sampling and detection methods have an immense influence on the ability of a laboratory to detect DF. Identification is more probable when the fecal samples are examined in three rather than one sample and is not possible without the use of a fixative agent such as SAF (sodium acetate / acetic acid / formalin). There is also debate about whether the detection rate is higher in soft or fluid stool. When stool slides are suitably stained there is a five fold increase in the rate of detection. Therefore, methods used in the detection of DF are of crucial importance.
Transmission of DF still remains unclear although there has been fair substantiation of the hypothesis that pinworms (E. vermicularis) are the vector responsible for person to person spread. DF forms have been documented in the lumen of pinworms found in the human appendix. Many authors have now reported a higher than anticipated co-incidence of DF and E. vermicularis infections. In fact, Ockert experimentally infected himself with pinworm eggs from a child and subsequently developed DF infection. Now thatís dedication! Two other successful attempts at infecting humans with DF from pinworms were also described by Ockert. By contrast infection with DF by ingesting DF trophozoites has failed.
Though the ability of DF to cause disease is still questioned by some, the circumstantial evidence incriminating this organism as a pathogen is overwhelming. Onset of infection is accompanied by onset of colicky pain, loss of appetite, soft stools covered with mucus and irritation of the rectum. Numerous observations have shown that treatment which eliminates the organism results in clinical improvement. In the literature, abdominal pain, persistent diarrhea, pruritus, abnormal stool with mucus, flatulence, fatigue or weakness, occasional eosinophilia, alternating diarrhea and constipation, nausea or vomiting, weight loss, constipation, belching and tenesmus are found in decreasing order of frequency as symptoms in patients in whom only DF was identified. Many of these symptoms mirror the symptoms of IBS.
Clinical suspicion of DF in patients with diarrhea predominant IBS needs to be confirmed by the demonstration of the parasite in stools. A laboratory which offers comprehensive stool testing should be used.
Trophozoites of DF degenerate rapidly and prompt fixation is necessary. In a laboratory aware of this organism, Giardia lamblia may be an uncommon pathogen by comparison, seen around 1/10 as commonly as DF. Hence, at least in clinical gastroenterological practice, DF is probably the most common detected parasite in some countries. Culture techniques are said to be the most sensitive method of detecting DF. However, few laboratories are capable of culturing DF at this stage.
Overall therefore, DF is infrequently sought for and is rarely detected using fresh, unfixed stool specimens.
Metronidazole (Flagyl), Tetracycline (Sumycin) and Iodoquinol (Vytone, Yodoxin) are all conventional drugs used in the treatment of DF.