Dientamoebiasis

Dientamoebiasis is a medical condition caused by infection with Dientamoeba fragilis, a single cell parasite that infects the lower gastrointestinal tract of humans. It is an important cause of traveler's diarrhea, chronic abdominal pain, chronic fatigue, and failure to thrive in children.

As many individuals are asymptomatic carriers of D. fragilis, pathogenic and nonpathogenic variants are proposed to exist. A study of D. fragilis isolates from 60 individuals with symptomatic infection in Sydney, Australia, found all were infected with the same genotype, which is the most common worldwide, but differed from the genotype first described from a North American isolate and later also detected in Europe.

Organisms similar to D. fragilis are known to produce a cyst stage that is able to survive outside the host and facilitate infection of new hosts. However, the exact manner in which it is transmitted is not yet known, as the organism is unable to survive outside its human host for more than a few hours after excretion, and no cyst stage has been found. Early theories of transmission suggested D. fragilis was unable to produce a cyst stage in infected humans, but some animal existed that in which it did produce a cyst stage, and this animal was responsible for spreading it. However, no such animal has ever been discovered. Experimental ingestion of pinworm eggs established infection in two investigators. Numerous studies reported high rates of coinfection with helminthes. However, recent study has failed to show any association between D. fragilis infection and pinworm infection. Parasites similar to D. fragilis are transmitted by consuming water or food contaminated with feces. The trophozoite forms have been recovered from formed stool, thus the need to perform the ova and parasite examination on specimens other than liquid or soft stools. DNA fragment analysis provides excellent sensitivity and specificity when compared to microscopy for the detection of D. fragilis and both methods should be employed in laboratories with PCR capability. The most sensitive detection method is parasite culture, and the culture medium requires the addition of rice starch. An indirect fluorescent antibody (IFA) for fixed stool specimens has been developed. One researcher investigated the phenomenon of symptomatic relapse following treatment of infection with D. fragilis in association with its apparent disappearance from stool samples. The organism could still be detected in patients through colonoscopy or by examining stool samples taken in conjunction with a saline laxative. A study found that trichrome staining, a traditional method for identification, had a sensitivity of 36% (9/25) when compared to stool culture. An additional study found that the sensitivity of staining was 50% (2/4), and that the organism could be successfully cultured in stool specimens up to 12 hours old that were kept at room temperature.

Concomitant pinworm infection should also be excluded, although the association has not been proven. Successful treatment of the infection with iodoquinol, doxycycline, metronidazole, paromomycin, and secnidazole has been reported. Although D. fragilis has been described as an infection "emerging from obscurity", it has become one of the most prevalent gastrointestinal infections in industrialized countries, especially among children and young adults. A Canadian study reported a prevalence of around 10% in boys and girls aged 11–15 years, a prevalence of 11.5% in individuals aged 16–20, and a lower incidence of 0.3–1.9% in individuals over age 20.

Early microbiologists reported that the organism was not pathogenic, though six of the seven individuals from whom they isolated it were experiencing symptoms of dysentery. Their report, published in 1918, concluded the organism was not pathogenic because it consumed bacteria in culture, but did not appear to engulf red blood cells, as was seen in the best known disease causing amoeba of the time, Entamoeba histolytica. This initial report may still be contributing to the reluctance of physicians to diagnose the infection.