European Food Safety Authority, via C.Magno 1, 43126, Parma, Italy,
Parasitol Res. 2013 Oct;112(10):3449-56. doi: 10.1007/s00436-013-3524-y. Epub 2013 Jul 28.
Giardia duodenalis isolates from German travellers returning from tropical areas were characterised by PCR amplification and sequencing of fragments of the beta-giardin (bg), glutamate dehydrogenase (gdh) and triose phosphate isomerase (tpi) genes. Assignment of isolates to specific G. duodenalis assemblages was found to differ according to the marker used. Indeed, at the bg locus, assemblages A and B were identified, with a higher prevalence of the former over the latter, whereas at the tpi and gdh loci, most samples were classified as assemblage B. In agreement with previous studies, sequence analysis showed that assemblage B isolates have a higher genetic polymorphism than assemblage A isolates, and novel variants were described. The degree of polymorphism was shown in a graphical representation of the polymorphic sites generating a novel sequence, the heterogeneous positions common to assemblages A and B (double peaks), that may represent mixed assemblage infection and the heterogeneous positions detected at random sites. Notably, assemblage D, which is considered to be adapted to dogs, was found at the gdh locus in two samples originating from southern Asia, as novel genotypes. By comparing the geographical origin of the infected cases and the number of German travellers visiting the areas considered, India and west Africa appeared to be the areas associated to the highest risk of acquiring Giardia infection. The analysis of the geographical distribution of the genotypes did not suggest any particular geographical clustering pattern, but it may be useful to evaluate these results with a higher number of isolates. Most of the samples typed at the three markers could not be assigned unequivocally to either assemblage A or B, and this was confirmed also by a real-time PCR assay, using a set of assemblage-specific primers. The results of this study reinforce the notion that genetic exchanges and allelic sequence heterogeneity represent major obstacles towards understanding the epidemiology of giardiasis and that exposure to Giardia parasites in endemic areas often results in mixed infections in returning travellers.
从前往热带地区旅行的德国旅行者中分离出的十二指肠贾第鞭毛虫，通过β-微管蛋白（bg）、谷氨酸脱氢酶（gdh）和磷酸丙糖异构酶（tpi）基因片段的 PCR 扩增和测序进行了特征描述。根据使用的标记，发现将分离株分配到特定的贾第虫属组合有所不同。事实上，在 bg 基因座上，鉴定出了 A 和 B 两个组合，前者比后者更为普遍，而在 tpi 和 gdh 基因座上，大多数样本被归类为 B 组合。与先前的研究一致，序列分析表明，B 组合分离株的遗传多态性高于 A 组合分离株，并且描述了新的变体。通过图形表示多态性位点生成新序列，显示了多态性程度，这些多态性位点是 A 和 B 组合共同的（双峰），可能代表混合组合感染，以及在随机位点检测到的异质位置。值得注意的是，被认为适应狗的 D 组合，在来自南亚的两个样本中，在 gdh 基因座上被发现是新的基因型。通过比较感染病例的地理起源和访问被认为是高风险地区的德国旅行者数量，印度和西非似乎是感染贾第虫的高风险地区。基因型的地理分布分析没有表明任何特定的地理聚类模式，但可能需要使用更多的分离株来评估这些结果。在三个标记上进行分型的大多数样本不能明确地分配到 A 组合或 B 组合，这也通过使用一组组合特异性引物的实时 PCR 检测得到了证实。这项研究的结果加强了这样一种观念，即基因交换和等位基因序列异质性是理解贾第虫病流行病学的主要障碍，并且在流行地区接触贾第虫寄生虫通常会导致返回旅行者的混合感染。
