ARTICLE
PARASITOLOGY
Detection of Dientamoeba fragilis and Blastocystis hominis from stool samples
Increased travel to and from countries in the tropics means that laboratories in the UK are increasingly likely to be asked to search for and identify faecal parasites. Here, Lisa Toole compares staining techniques.
Parasitic diseases are a major cause of human infection worldwide, in particular in the tropics. Diseases resulting from helminths and protozoa can cause suffering to billions of people and kill millions annually.1 Blastocystis hominis was first described by Alexeieff in 1911, while Dientamoeba fragilis was described by Jepps and Dobell in 1918;2 however, since their discovery, much about them remains poorly understood.3
Although
these parasites are thought to be non- pathogenic, many emerging reports now associate D. fragilis and B. hominis with gastrointestinal symptoms.4
have isolated these parasites together,5,6 Many studies and
they have also been linked to irritable bowel syndrome.4,7
Studies suggest that a fixed, stained smear is essential for adequate identification of D. fragilis and B. hominis as internal structures are difficult to detect in saline and
iodine wet preparations.8 Therefore, the aim
this small study is to assess the prevalence of D. fragilis and B. hominis with evaluation of an adaptation of a fluorescence staining technique, together with analysis of a range of patient variables to establish if any correlations exist.
MATERIALS AND METHODS Analysis of 200 consecutive clinical stool samples received at the Manchester Royal Infirmary between 1 June 2012 and 1 August 2012 was performed. In brief, two air-dried smears were prepared, prefixed in 10% formalin-water for each sample. One was stained with acridine orange (Pro-Lab) and the other using the Rapid Diff-3 kit (Avonchem Diagnostics). Both slides were viewed under x50 magnification (Leica DM400 microscope) and the results were recorded by photomicrography. The prevalence of
D. fragilis and B. hominis, the significant difference in performance between the stains, and numerous patient variables were analysed. Giardia lamblia was used as the positive
control to assess staining performance, and was supplied by UK NEQAS. A second parasitologist confirmed all results and the presence of G. lamblia was confirmed using an enzyme-linked immunosorbent assay (ELISA) method (Alere).
RESULTS
Of the 200 specimens examined, seven were positive for parasites and nine target organisms were detected: D. fragilis 2% (n=4), B. hominis 2.5% (n=5) and D. fragilis/B. hominis co-infection 1% (n=2). Comparison of acridine orange stain and
the Rapid Diff-3 kit showed that acridine orange performed better than the Rapid Diff-3 kit in detecting B. hominis: acridine orange 2.5% (n=5) compared to the Rapid Diff-3 kit 1.5% (n=3). Both stains detected the 2% (n=4) D. fragilis and 1% (n=2) co-infection. Acridine orange also detected a wider range of enteric parasites. No significant differences were seen in the majority of patient variables; however,
2.0% 1.0% 2.5% B. hominis D. fragilis Co-infection Prevalence data for D. fragilis and B. hominis. 726 THE BIOMEDICAL SCIENTIST Acridine Orange Stain
Negative Giardia Various non-pathogenic cysts B. hominis
Rapid Diff-3 Stain
D. fragilis C. mesnili E. nana Co-infection
Visual representation of results obtained by both stains. DECEMBER 2013
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