Molecular epidemiology of Blastocystis infections in Turkey

doi:10.1016/j.parint.2008.01.004

Parasitology International

Volume 57, Issue 3, September 2008, Pages 300-306

https://doi.org/10.1016/j.parint.2008.01.004 Get rights and content

Abstract

Blastocystis is a very common unicellular intestinal parasite of ubiquitous occurrence. In order to describe the molecular epidemiology of Blastocystis infections in Turkey, 87 isolates from 69 symptomatic and 18 asymptomatic individuals were sequenced. Sequence data were phylogenetically analyzed and statistically tested against unmodifiable risk factors such as gender and age. Blastocystis-positive males were complaining mainly of gastroenteritis, whereas dyspepsia was the chief complaint among Blastocystis-positive females. Blastocystis sp. subtypes detected in the study included subtypes 1, 2, 3 and 4, subtype 3 being the most predominant (75.9%). No association was detected between Blastocystis sp. subtype and symptoms (p > 0.365), or between infection intensity and symptoms (p > 0.441). There was a tendency of subtype 2 isolates being more common among older study individuals, and subtype 2 isolates were significantly associated with higher parasite abundance (p = 0.017).

Compared to data from similar studies, the distribution of Blastocystis sp. isolates in Turkey was found to more or less reflect the one seen in other countries, and it was deduced that subtype 3 is generally by far the most common subtype infecting humans, followed by subtypes 1, 2 and 4.

Introduction

Little is known about the public health significance of Blastocystis infections. Blastocystis[1] is probably the most common eukaryotic organism in the gastrointestinal tract of humans [2] and prevalence estimates reach approximately 60% in some developing countries [3]. The genus of Blastocystis exhibits extensive genetic diversity [4] comprising isolates which differ genetically by more than 7%. Based on molecular analysis of the small subunit (SSU) rRNA gene, Blastocystis isolates from humans, mammals and birds can each be assigned to one of at least nine subtypes [5], all of which have been isolated from humans [6], [7], [8]. It is hypothesized that the pathogenicity of Blastocystis might depend on subtype [4], [9], [10].

DNA-based methods are essential to detect genetic variation between Blastocystis organisms, which seem to be morphologically undistinguishable. During the last decade, molecular methods for the detection of Blastocystis have been developed (summarized in [5]). Despite these methodological improvements, very few studies have sought to unravel the molecular epidemiology of Blastocystis infections. Molecular epidemiological studies are particularly relevant in the case of Blastocystis, since such studies will yield vital information on aspects regarding transmission patterns, host specificity, chemotherapeutic drug resistance, and, probably most important of all, public health significance; all being aspects that until now have been more or less uncovered.

A few studies have focused on the prevalence of Blastocystis subtypes among asymptomatic and symptomatic individuals [9], [10], [11], [12] and a recent study sought to describe the molecular epidemiology of Blastocystis infections in a rural community in China [13].

A recent study by Stensvold et al. [14] comparing parasitological detection with PCR-based detection of Blastocystis, showed that particularly subtype 3 isolates tend to be missed by standard parasitological techniques, and it was speculated that Blastocystis sp. subtypes differed in terms of infection intensity and/or cyst formation.

The present study aimed to characterize Blastocystis isolates from Turkish patients who where admitted to a tertiary hospital and who submitted stools for parasitological examination in order to compare the subtype distribution in Turkey with the one seen in other countries and to test whether some subtypes were associated with the presence of distinct intestinal symptoms. It was also a goal to test the hypothesis that Blastocystis infection intensity detected by microscopy is independent of Blastocystis sp. subtype.

Section snippets

Identification of Blastocystis-positive individuals

Over a period of 8 months, a total of 105 patients with varying intensities of Blastocystis infection were identified by examination of fresh stool samples; the patients had been referred from in- and outpatient departments of Haydarpasa Training Hospital of Gulhane Military Medical Academy, a tertiary hospital admitting both military and civil patients from all areas of Turkey. The asymptomatic group comprised of food handlers (cook, waiter and other workers in the kitchen of the hospital's or

Results

Faecal samples were available from 105 individuals, 102 of whom were positive for PCR bands initially considered to be specific for Blastocystis by one of the two PCR assays. In 9 instances, however, readable sequences could not be obtained by repeated dideoxysequencing, and in 6 cases, nucleotide sequences specific for Saccharomyces cerevisiae or Candida sp. were obtained; in these 15 instances, PCR analysis using the Bl1400ForC and Bl1710RevC primers [14] was negative. Consequently, the

Discussion

This is one of the few major studies to date seeking to describe the molecular epidemiology of Blastocystis infections and unravel any potential association between Blastocystis sp. subtypes and symptom status including statistical adjustment for gender and co-infection with other intestinal protozoa.

The specificity of traditional parasitological techniques such as trichrome staining and formol ethyl acetate concentration has previously been shown to be comparable to that of PCR [8]. In the

Conclusion

The subtype distribution of the Blastocystis sp. in Turkey bears a high resemblance to the one seen in other countries, although unique subtype variants are seen. Drawing on results from the present and similar studies comprising a total of 390 isolates, it was established that human Blastocystis infection is mainly due to subtype 3 isolates, but subtypes 1, 2 and 4 are also found. It is therefore reasonable to believe that subtypes 5–9 are only sporadically causing infection in humans.

Subtype

Acknowledgements

The authors are deeply thankful to Lis Lykke Wassmann and her colleagues at the Laboratory of Parasitology, Statens Serum Institut, Copenhagen, Denmark, for carrying out the molecular analyses.

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View full text

Molecular epidemiology of Blastocystis infections in Turkey

Abstract

Introduction

Section snippets

Identification of Blastocystis-positive individuals

Results

Discussion

Conclusion

Acknowledgements

Mol Biochem Parasitol

Trends Parasitol

Diagn Microbiol Infect Dis

Parasitol Int

Vet Parasitol

Vet Parasitol

Mol Biochem Parasitol

Trends Parasitol

Blastocystis hominis n.sp. et formes voisines

Bull Soc Pathol Exot

Cryptic genetic variation in parasitic protozoa

J Med Microbiol

Parasitological and nutritional situation of school children in the Sukaraja district, West Java, Indonesia

Southeast Asian J Trop Med Public Health

Molecular phylogenies of Blastocystis isolates from different hosts: implications for genetic diversity, identification of species, and zoonosis

J Clin Microbiol