Kate Johnson

May 14, 2014

BARCELONA, Spain — New research on the intestinal parasite Dientamoeba fragilis has added fuel to the debate about the pathogenicity of the controversial protozoan.

The multicenter study found higher rates of the parasite in healthy control subjects than in patients with gastrointestinal symptoms, suggesting that the organism is not harmful and should not routinely be eradicated — a view that has long been debated.

"We were very much surprised — and puzzled — by this finding," said investigator Bert Mulder, MD, PhD, from the Laboratory of Microbiology and Public Health in Hengelo, the Netherlands. "I would say it's bad news for those who think it is a pathogen," he told Medscape Medical News.

The study was presented here at the 24th European Congress of Clinical Microbiology and Infectious Disease.

Researchers evaluated stool samples collected over 2 years from patients of general practitioners. The 1542 samples from patients with gastrointestinal symptoms were compared with 1203 samples from age-, sex-, and region-matched control subjects with no gastrointestinal complaints.

Using highly sensitive molecular diagnostic testing, the researchers determined that rates of D fragilis alone were lower in the gastrointestinal patients than in control subjects (17.8% vs 32.4%), as were rates of D fragilis mixed with other organisms (25.3% vs 37.1%).

However, rates tended to be higher in the gastrointestinal patients than in control subjects for most other parasites and bacteria, including Cryptosporidium (3.0% vs 0.8%), Giardia lamblia (5.5% vs 2.7%), and Campylobacter (9.9% vs 2.8%).

When D fragilis was the only organism detected, the gastrointestinal patients with D fragilis reported less diarrhea than than those without the parasite (59.6% vs 78.7%).

DNA concentrations of the parasite, according to CT values, were similar in the 2 groups. "We do not have an explanation for our findings. We were as surprised as the audience here," said Dr. Mulder.

"With a pathogen, you expect to find more DNA in the cases than controls, but for D fragilis we did not; you expect to find more prevalence in cases, but we found more in controls; and you expect more clinical signs and symptoms in the cases, but we found less diarrhea," he reported.

It is possible that the parasite protects against diarrhea, or that diarrhea washes out the parasite, he explained.

Because of difficulty obtaining enough control samples, a subgroup of 39 control samples were obtained from the research group's laboratory technicians. There was more D fragilis in this subgroup than in the rest of the control group, but the rates of other parasites and organisms were similar in the subgroup and the rest of the control group.

There was a slightly lower rate of Shiga toxin-producing Escherichia coli in the gastrointestinal patients than in the control subjects (1.0% vs 1.8%). "No one thinks that thisis not a pathogen; there a 6 pathogenic subtypes and hundreds of nonpathogenic types," Dr. Mulder said.

The typing of D fragilis should be the next step next step toward explaining some of these results and to see if there are different subtypes in the gastrointestinal patient and control groups, he said.

In light of the findings, his laboratory has dropped D fragilis from its molecular diagnostics panel for patients with gastroenteritis. "We conclude that there is an enormous overdiagnosis of D fragilis because of the introduction of molecular diagnostics in the Netherlands," he explained.

However, he does not rule out the possibility that in some cases — perhaps with certain strains — D fragilis can be pathogenic.

"I still believe there might be a subgroup — mainly children — with abdominal cramps and no other explanation that might be caused by D fragilis, but this is not found by testing every GI patient. This is only found when specific complaints lead to a specific request from the pediatrician," he said.

"These findings are in agreement with several studies that have been performed in Denmark," said Dennis Röser, MD, from Statens Serum Institut in Copenhagen, who is preparing to defend his PhD thesis on the pathogenicity of D fragilis.

"I'm not convinced that it is a pathogen. If it is, it's likely a mild one," he told Medscape Medical News.

Dr. Röser was involved in a study of more than 22,000 samples collected for routine parasitosis work-ups (Eur J Clin Microbiol Infect Dis. 2013;32:1303-1310). The team found a "staggeringly" high level of D fragilis (43%) overall, with a peak of 71% in 7-year-old children and another peak in "parental adults" 35 to 40 years of age.

In ongoing work, Dr. Röser's team has found even higher rates in healthy kindergarten children.

Although many clinicians and guidelines advocate routine treatment for D fragilis, this practice is not evidence-based, he explained. The few published studies on treatment have failed to correlate microbiologic eradication with symptom improvement.

Medscape Medical News contacted one of the strongest proponents of the pathogenicity of D fragilis — Damien Stark, PhD, from St. Vincent's Hospital in Darlinghurst, Australia. However, Dr. Stark said he was reluctant to comment on the study without seeing more details.

Dr. Mulder and Dr. Röser have disclosed no relevant financial relationships.

24th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID): Abstract O051. Presented May 11, 2014.


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