Dientamoeba fragilis

A nonflagellate trichomonad parasite.

Estimated prevalence in the United States is 2-4%.

Much higher prevalence in individuals living in crowded and poor hygeine conditions, and those traveling to developing countries.

In adults, asymptomatic colonization is present in 75-85% of individuals affected by the parasite.

In children the disease develops in as many as 90% of those colonized.

Infection not associated with mortality.

Predominant symptom is diarrhea.

Chronic infection occurs after 1-2 months of infection and is associated with abdominal pain.

The infection may occur at any age but is most common in children is 5-10 years.

One of the smaller parasites that can live in the human large intestine.

Its life cycle has no cyst stage and infection between humans occurs during the trophozoite stage.

Organisms move most actively in fresh feces.

Organisms are sensitive to an aerobic environment, and die when placed in saline, tap water, or distilled water.

Transmission is believed to be through direct fecal-oral spread and, possibly, through coinfection of eggs of Enterobius vermicularis.

Organisms infect mucosal crypts from the cecum to the rectum.

The cecum and proximal colon are usually affected.

The parasite is not known to be invasive and does not cause cellular damage.

It may cause an eosinophilic inflammatory response in the colonic mucosa.

Symptoms are related to the superficial colonic mucosal irritation.

Abdominal pain and diarrhea are the most common symptoms.

In acute infection, duration of symptoms is 1-2 weeks.

Diarrhea predominates in acute infection.

In chronic infection symptoms lasts longer than 1-2 months, and abdominal pain is more common.

Common complaints include: anorexia, nausea, vomiting, bloating, and fatigue.

Blood test results are usually normal but may show eosinophilia.

Diagnosis is confirmed by examination of fresh feces, preserved immediately, for the morphologic characteristics of D fragilis trophozoites.

Immediate preservation is necessary as the morphologic characteristics of the trophozoites do not persist in a non-preserved specimen.

A single sample is diagnostic only 50-60% of the time and three samples increase the yield to 70-85%, and 6 samples increase the yield to 90-95%.

Medications that can interfere with parasite detection.

Diagnostic characteristics are a pleomorphic trophozoite and the most common form is binucleated.

Trophozoites may be uninucleated 20-30% of the time and multinucleated forms also can be present.

Treatment includes: Metronidazole, tetracycline, Iodoquinol, paromomycin,

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