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Dientamoeba Fragilis: Some Further Observations

Some observations upon the incidence, duration of infection, diagnosis, clinical findings, and treatment of D. fragilis infections have been presented, as well as a report of some attempts to find encysted forms.

Incidence. In a group of thirty-eight inmates of an insane asylum, sixteen new infections with D. fragilis occurred during the course of one year, an annual rate of 42.1 per cent. Two instances of familial infection are recorded, in a Panamanian family of nine members four had D. fragilis, and in a white family of four including two children less than ten years of age, all had the infection.

Duration of infection. It was found that some D. fragilis infections apparently terminated spontaneously. The shortest period to which our methods of examination limited any infection was two weeks. One infection, the presence of which was checked at least once a week, lasted a year and a half. Several infections have been observed for a year and are still current.

Diagnosis. D. fragilis has been found to be the most readily recognized trophozoite of the intestinal amoebae. Not only can it be identified positively on its characteristic nuclear system in wet-fixed stained preparations but even in unstained wet smears it presents diagnostic features which are so constant that identification is practically always possible. Mushy stools passed normally or after mild laxatives contain the amoeba most frequently and in the largest numbers. In some infections D. fragilis at times becomes very rare even in these stools and its detection may then be a difficult task.

Clinical findings. Clinical histories were obtained from 12 cases. Six of these complained of some intestinal distress which, however, may not have been caused by the D. fragilis infection.

Treatment. Six adults were treated with carbarsone, 0.50 gram twice daily for two days, a total of 2 grams. In five of these, D. fragilis apparently was eradicated by one course. The sixth case received three courses before the infection disappeared. There was a probability that in this case reinfections rather than recurrences occurred after the first two courses.

The absence of cysts. Having recognized the possibility that in stained smears from fecal samples some trophozoites may resemble and be mistaken for cysts our search for encysted forms of D. fragilis was made after the trophozoites had been destroyed in water. More than a thousand aqueous smears and 168 concentrations made from stools of individuals who carried the infection failed to reveal any bodies that possibly could have been cysts of D. fragilis. Cultures from six concentrates were also negative.

Received March 17, 1937.
¹ The writer is indebted to H. A. Down and L. E. Boston of the Hospital Corps, United States Navy, for valuable technical assistance.