Introduction
Various novel studies have revealed that Dientamoeba fragilis is a widespread organism with a prevalence rate as high as 8.9 to 16.8 percent in developing countries. The symptoms of Dientamoeba fragilis infection commonly include diarrhea and abdominal pain. Cases of chronic infections are often reported. Recent studies have proved antimicrobial therapy for D. fragilis has shown great improvement in patients with this infection.
What Is the Causative Agent of Dientamoeba Fragilis Infection?
Dientamoeba fragilis is not an ameba. Instead, it is an intestinal flagellate related to trichomonads. D. fragilis is often found mainly as a trophozoite in human stool samples. However, it has been reported that in rare cases, precysts and putative cysts forms are found in clinical specimens. The transmission of this infection has not been fully understood yet. Infection can occur at any age. The infection is most commonly reported in children between the age group of five to ten years.
What Is the Epidemiology of This Infection?
The prevalence of this infection in the United States and other developed countries is around two to five percent. However, the prevalence rates are higher in the following populations (approximately 19 to 69 percent):
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People living in crowded conditions (institutions and communal living).
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Individuals living in conditions with poor hygiene.
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People traveling to developing countries.
Mortality or Morbidity:
No specific mortality rate is associated with this infection. Morbidity is related to acute infection and occurs within the first two weeks of the infection.
What Are the Clinical Features of Dientamoeba Fragilis Infection?
The most common symptoms in patients with Dientamoeba fragilis infection include:
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Abdominal pain.
The history of diarrheal episodes may differ in frequency or occurrence.
The consistency of the stool varies from sticky to watery and is usually greenish brown. Sometimes mucus can also be present in the stool. However, hematochezia (the passage of fresh blood through the anus with stools) is not commonly seen.
Diarrhea is the predominant symptom in acute infection lasting for one to two weeks.
Chronic infection is reported when symptoms occur for more than one to two months and are manifested by abdominal pain.
Nonintestinal problems include:
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Malaise.
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Weakness.
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Headache.
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Fever.
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Pruritus.
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Fatigue.
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Irritability.
Gastrointestinal problems include:
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Nausea.
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Vomiting.
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Anorexia.
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Weight loss.
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Bloating.
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Alternating episodes of constipation and diarrhea.
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Flatulence.
How Is Dientamoeba Fragilis Transmitted?
The infection is transmitted through the fecal-oral route and can also be spread by the eggs of pinworm. Recently pigs have been identified as the natural host of this infection. Therefore the possibility of spread through swine waste has increased. Dientamoeba fragilis has also been found in untreated wastewater.
How Is Dientamoeba Fragilis Infection Diagnosed?
The infection can be diagnosed by the following methods:
1. Stool Examination:
Examination of a permanently stained smear of fresh feces is the common method for diagnosing this infection. The following new techniques can also be employed to examine the stool:
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Immunofluorescence.
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Real-time polymerase chain reaction (PCR).
In this infection, culture is not performed routinely.
Stool preparation for examination is done by the following method:
A. A fresh sample of stool is preserved in one of the below fixatives:
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Sodium acetate-acetic acid-formalin fixative.
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Polyvinyl alcohol fixative.
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Schaudinn fixative.
B. The organism becomes granular at room temperature within 15 minutes. Immediate preservation is necessarily required as the morphologic characteristics of the trophozoites are altered in unpreserved feces.
C. The diagnostic capacity of a single sample is 50 to 60 percent of the time. Three separate samples increase the diagnostic capacity to 70 to 85 percent, and six samples show 90 to 95 percent diagnostic capacity.
D. The stool samples must be collected on alternate days as the organism is excreted in a cyclic pattern like Giardia lamblia.
E. Certain medications can interfere with the detection of this organism. These medications include:
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Antibiotics.
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Antimalarial.
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Antiprotozoal medication.
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Mineral oil.
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Bismuth-containing preparations.
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Nonabsorbable diarrheal medications.
2. Blood Tests:
Patients with Dientamoeba fragilis infection usually have normal blood test results.
However, a CBC count shows eosinophilia in around 50 percent of children infected with the parasite.
3. Diagnostic Characteristics:
Diagnostic characteristics include:
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Pleomorphic trophozoite with a diameter ranging from 5 to 15 millimeters.
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It contains one to four nuclei (it is mostly binucleated). However, around 20 to 30 percent are uninucleated. Multinucleated forms also can be present.
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The nuclei are distinctive, with four to eight chromatin granules clumped in the center of each nucleus. The cytoplasm frequently contains numerous food vacuoles.
How Is Dientamoeba Fragilis Infection Managed?
The drugs used for the treatment of this infection are still under consideration by the United States Food and Drug Administration because of a lack of clinical trials. For a single course of therapy, the response rates are 70 to 90 percent.
Current recommendations for therapy include the following drugs:
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Iodoquinol (drug of choice).
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Tetracycline (inhibits bacterial protein synthesis).
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Paromomycin (amebicidal and antibacterial aminoglycoside derived from a strain of Streptomyces rimosus).
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Metronidazole (imidazole ring-based antibiotic. It acts against anaerobic bacteria and protozoa).
In the United States, the availability of Paromomycin and Iodoquinol is limited.
New drugs that are effective in a single dose with few side effects and longer half-lives include:
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Secnidazole.
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Ornidazole.
Drugs that show in vitro activity against D. fragilis:
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Tinidazole.
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Ronidazole.
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Nitazoxanide.
Conclusion
There is a continuous debate about whether the organism is a pathogenic or harmless commensal. Some studies show that eosinophilia was found among 50 percent of the infected children. The symptoms may be due to irritation caused by colonic motility, which does not penetrate the host tissue. In some instances, the eosinophilia may be related to pinworm and co-infections with other parasites.
Anyone can develop this infection. However, the risk for infection might be higher for individuals who travel to or live in regions with poor sanitary conditions. Hands must be washed with soap and warm water after changing diapers, using the toilet, and eating food. Children must be taught the importance of hygiene maintenance to avoid this infection.
D. fragilis is commonly found in children's stools, but its clinical importance is not yet understood. It does not lead to any medical complications for children who carry it due to its noninvasive nature, and no ill effects have been associated with its chronic carriage.
