Subtype analysis of Blastocystis isolates in Swedish patients
Blastocystis is a genetically diverse and widespread intestinal parasite of animals and humans with controversial pathogenic potential. At least nine subtypes of Blastocystis have been found in humans. The genetic diversity of Blastocystis was examined in stool samples from 68 patients from the Stockholm area, Sweden. Blastocystis was identified by light microscopy, and subtyped by sequencing the 5'-end of the small subunit ribosomal RNA gene. Five Blastocystis subtypes were identified in the 63 patients whose samples were successfully subtyped: ST1 (15.9%), ST2 (14.3%), ST3 (47.6%), ST4 (20.6%), and ST7 (1.6%). ST3 was more common in males compared to females (P=0.049). Comparative molecular analysis of Blastocystis sequences revealed intra-subtype variations within the identified subtypes with the exception of ST4. Among ST4 sequences in this study, as well as in the majority of human GenBank sequences, a limited genetic diversity was found compared to what was found among the other common subtypes (ST1, ST2 and ST3). The relative prevalence of ST4 in this study was comparable to the overall distribution of ST4 in European cohorts (16.5%). This contrasts with the sparse reports of ST4 in studies from other continents, which may indicate that the distribution of this subtype is geographically heterogeneous.
Available from: Lobna Gaayeb
- "Interestingly ST4 was not detected in the studies reported in Egypt, Libya and Tanzania and its prevalence is quite low in Senegal (1.9%). Although ST4 was relatively frequent in Liberia (12%) and Nigeria (14%), these data confirmed that ST4 is much less frequently detected or absent in Africa while it is commonly found in Europe
[5,34]. However, the reasons for the heterogeneous geographical distribution of ST4 remain unknown and its reservoir hosts have to be clarified. "
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ABSTRACT: Blastocystis sp. is currently the most common intestinal protist found in human feces and considered an emerging parasite with a worldwide distribution. Because of its potential impact in public health, we reinforced the picture of Blastocystis sp. prevalence and molecular subtype distribution in Africa by performing the first survey of this parasite in Senegal.
Stool samples from 93 symptomatic presenting with various gastrointestinal disorders or asymptomatic children living in three villages of the Senegal River Basin were tested for the presence of Blastocystis sp. by non-quantitative and quantitative PCR using primer pairs targeting the SSU rDNA gene. Positive samples were subtyped to investigate the frequency of Blastocystis sp. subtypes in our cohort and the distribution of subtypes in the symptomatic and asymptomatic groups of children.
By the use of molecular tools, all 93 samples were found to be positive for Blastocystis sp. indicating a striking parasite prevalence of 100%. Mixed infections by two or three subtypes were identified in eight individuals. Among a total of 103 subtyped isolates, subtype 3 was most abundant (49.5%) followed by subtype 1 (28.2%), subtype 2 (20.4%) and subtype 4 (1.9%). Subtype 3 was dominant in the symptomatic group while subtypes 1 and 2 were detected with equal frequency in both symptomatic and asymptomatic groups. The distribution of subtypes was compared with those available in other African countries and worldwide. Comparison confirmed that subtype 4 is much less frequently detected or absent in Africa while it is commonly found in Europe. Potential sources of Blastocystis sp. infection including human-to-human, zoonotic, and waterborne transmissions were also discussed.
The prevalence of Blastocystis sp. in our Senegalese population was the highest prevalence ever recovered worldwide for this parasite by reaching 100%. All cases were caused by subtypes 1, 2, 3 and 4 with a predominance of subtype 3. More than half of the children infected by Blastocystis sp. presented various gastrointestinal disorders. Such high prevalence of blastocystosis in developing countries makes its control a real challenge for public health authorities.
Available from: Aldert Bart
- "Various studies have identified ST3 as the predominant subtype, as was true for our study population. Subtype 4 was relatively frequent in our study group (12%) as compared to studies worldwide , although a more similar prevalence of this subtype was observed in studies from Europe . The differences in relative abundance of the subtypes 1-4 suggests that differences in transmission efficiency may exist between them. "
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ABSTRACT: Blastocystis sp. are among the most commonly observed intestinal parasites in routine clinical parasitology. Blastocystis in humans consists of at least 9 genetic subtypes. Different subtypes of Blastocystis may be associated with differences in pathogenicity and symptomatology.
Advanced microscopy on two samples and sequence-confirmed PCR on a third sample from the same individual were used for Blastocystis diagnosis and subtype analyses on routine clinical samples in a university hospital.
With a combined gold standard of sequence-confirmed PCR and positive advanced microscopy, 107 out of 442 (24.2 %) patients were diagnosed with Blastocystis. infection, which is a high frequency of detection in comparison to previous reports from industrialized countries. The sensitivity of microscopy and sequence-confirmed PCR was 99.1 % (106/107) and 96.3 % (103/107), respectively.Among 103 typable samples, subtype 3 was most abundant (n = 43, 42%), followed by subtypes 1 and 2 (both n = 23, 22%), subtype 4 (n = 12, 12%), and single samples with subtypes 6 (1%) and subtype 7 (1%). The prevalence of Blastocystis infection was 38% in patients from the Department of Tropical Medicine and 18% in patients from other departments.
A high prevalence of Blastocystis infection was found with both advanced microscopy and sequence-confirmed PCR in our patient population. Most cases were caused by subtypes ST1, ST2, ST3 and ST4. A significantly higher prevalence was found among patients with a history of recent travel to tropical countries.
Available from: Christen Rune Stensvold
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ABSTRACT: Blastocystis is a common single-celled parasite of humans and other animals comprising at least 13 genetically distinct small subunit ribosomal RNA lineages (subtypes (STs)). In this study we investigated intra-subtype genetic diversity and host specificity of two of the most common subtypes in humans, namely ST3 and ST4, by analysing and comparing over 400 complete and partial nuclear SSU-rDNAs and data from multilocus sequence typing (MLST) of the mitochondrion-like organelle (MLO) genome of 132 samples. Inferences from phylogenetic analyses of nuclear SSU-rDNA and concatenated MLST sequences were compatible. Human ST3 infections were restricted to one of four identified MLO clades except where exposure to non-human primates had occurred. This suggests relatively high host specificity within ST3, that human ST3 infections are caused predominantly by human-to-human transmission, and that human strains falling into other clades are almost certainly the result of zoonotic transmission. ST4 from humans belonged almost exclusively to one of two SSU-rDNA clades, and only five MLST sequence types were found among 50 ST4s belonging to Clade 1 (discriminatory index: 0.41) compared to 58 MLST sequence types among 81 ST3s (discriminatory index: 0.99). The remarkable differences in intra-subtype genetic variability suggest that ST4 has a more recent history of colonising humans than ST3. This is congruent with the apparently restricted geographical distribution of ST4 relative to ST3. The implications of this observation are unclear, however, and the population structure and distribution of ST4 should be subject to further scrutiny in view of the fact ST4 is being increasingly linked with intestinal disease.
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