Dientamoeba fragilis
=1.
Classification
Higher order taxa
Kingdom Excavata, Subkingdom Metamonada, Phylum Parabasalia, Class Tritrichomonadidae, Order Trichomonadida, Family Dientamoebidae
Species
Dientamoeba fragilis
2. Description and significance
Dientamoeba fragilis (D. fragilis) is a bacterium regarded as a human intestinal parasite. There is a possible link between D. fragilis colonization and abnormal gastrointestinal symptoms (1) ; however, some studies show that there is no causal relationship (2). D. fragilis has a worldwide distribution in both urban and rural areas, with infection rates ranging from 0.5% to 16%, where higher rates were reported in outbreaks and associated to the lack of personal hygiene(3). Similar to some other parasites, D. fragilis causes disease in humans regardless of their immune status, by which common symptoms include abdominal pain and diarrhea. D. fragilis has been increasingly recognized as a relatively common cause of human diarrhea and long-term chronic infections since the late twentieth century(3).
3. Genome structure
Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence?
4. Cell structure
Interesting features of cell structure. Can be combined with “metabolic processes”
5. Metabolic processes
Describe important sources of energy, electrons, and carbon (i.e. trophy) for the organism/organisms you are focusing on, as well as important molecules it/they synthesize(s).
6. Ecology
D. fragilis is often regarded as a human parasite which causes abnormal gastrointestinal symptoms such as abdominal pain and diarrhea(8). It is commonly found in human bile and feces, which suggests that it thrives in small and large intestines, as well as the gallbladder(9). D. fragilis is anaerobic bacteria; therefore, it is very sensitive to aerobic environment(8). It may not survive and reproduce after it leaves the host body, so it nearly does not exist in the outside environment. Besides, similar to many other kinds of microbes, D. fragilis does not thrive alone: it is likely to build a dependent relationship with Entamoeba histolytica(8).
7. Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
8. Current Research
The pathogenicity of D. fragilis is controversial. Some research provides evidence that D. fragilis is a human pathogenic bacterium, which causes gastrointestinal symptoms(8), while others argue that D. fragilis is just a common asymptomatic parasite(11).
(a) D. fragilis is a pathogenic parasite
D. fragilis was usually regarded as a harmless parasite that does not cause abnormal gastrointestinal symptoms. However, its pathogenicity was explored through recent researches. The colonization of D. fragilis among patients with gastrointestinal symptoms was evaluated through stool analysis, and it was compared to a better-known intestinal parasite Giardia lamblia (G. lambila). The result showed that the prevalence and pathogenicity of D. fragilis is similar to G. lambila: D. fragilis is a potential cause of gastrointestinal symptoms(1). Moreover, D. fragilis is considered as a pathogen based on a report which focuses on a family cluster of D. fragilis-related illness and asymptomatic carriage(12). The report conducted five case studies within one family regarding complete blood count (CBC) and fecal specimen analysis. The results found linkage between detection of D.fragilis and marked peripheral eosinophilia, often associated as response to allergens and indicates activation of the immune system. Besides, D. fragilis was the only consistent finding in all family members involved in this cluster, all shown gastrointestinal symptoms(3).
(b) D. fragilis is a harmless parasite
Though many researches provide evidence about the pathogenicity of D. fragilis, some researchers insist that D. fragilis is a harmless intestinal parasite. One study explores the causal relationship between the presence of D. fragilis and gastrointestinal symptoms among children in primary care setting(11). A cross-sectional study among children with D. fragilis infection using logistic regression analysis as well as a control analysis using asymptomatic siblings of the subjects was conducted. The conclusion is that D. fragilis is not a pathogenic parasite which causes abdominal pain and diarrhea; instead, it is a common intestinal parasite which does not cause gastrointestinal symptoms(11). Furthermore, a study compares several reports based on the prevalence of D. fragilis in individuals with and without diarrhea. Based on the statistic results, it shows that only a proportion of subjects with D. fragilis infection is present with diarrhea symptoms. Vice versa, out of the entire study population with diarrhea symptoms, only a small percent of them was detected with D. fragilis infection. These research states that the pathogenicity of D. fragile isn’t conclusive due to lack of a systematic study on the organism’s treatment and resolution(13).
(c) Possible Treatments for D. fragilis infection
Diiodohydroxyquin, tetracycline, metronidazole and paromomycin are common treatments for eradicating D. fragilis colonization, and treatment period is between 5 to 21 days. In particular, study on paromomycin show promising efficiency in treatment. It was evaluated by examining feces for D. fragilis and other intestinal parasites after 28 days of treatment, and 80% and 87% infected study subjects shown parasitologically and clinically recovered. D. fragilis infection symptoms such as abdominal pain and diarrhea were reported to be relieved after taking paromomycin(14). Furthermore, Secnidazole is suggested as a relatively novel, more effective treatment compared to the other drugs. It has a short half-life, therefore only a single-dose is required in most of the cases to eradicate D. fragilis infection(1). This drug is suggested to take after dinner to avoid possible nausea and vomiting, and it does not severe side-effects except for occasional mild nausea(1).
9. References
It is required that you add at least five primary research articles (in same format as the sample reference below) that corresponds to the info that you added to this page. [Sample reference] Faller, A., and Schleifer, K. "Modified Oxidase and Benzidine Tests for Separation of Staphylococci from Micrococci". Journal of Clinical Microbiology. 1981. Volume 13. p. 1031-1035.
