Cacciò Simone M, Ryan Una
Department of Infectious, Parasitic and Immunomediated Diseases, Istituto Superiore di Sanità, Viale Regina Elena 299, Rome, Italy.
Mol Biochem Parasitol. 2008 Aug;160(2):75-80. doi: 10.1016/j.molbiopara.2008.04.006. Epub 2008 May 5.
Giardia duodenalis is a widespread parasite of mammalian species, including humans. Due to its invariant morphology, investigation on aspects such as host specificity and transmission patterns requires a direct genetic characterization of cysts/trophozoites from host samples. A number of molecular assays have been developed to help unravel the complex epidemiology of this infection. A coherent picture has emerged from those studies, indicating the existence of seven genetic groups (or assemblages), two of which (A and B) are found in both humans and animals, whereas the remaining five (C-G) are host-specific. Sequence-based surveys have identified a number of genotypes within assemblages A and B in animal species, some of which may have zoonotic potential. Recently, however, molecular approaches have been complicated by the recognition of intra-isolate sequence heterogeneity (i.e., "mixed templates", that affects identification of subtypes within each assemblage), and by the unreliable assignment of isolates to G. duodenalis assemblages generated by different genetic markers. This raises concerns about previous interpretation of genotyping data, especially when single genetic markers have been used. The mechanisms that may be responsible for these findings, including allelic sequence heterozygosity and meiotic recombination, are discussed.
十二指肠贾第虫是一种广泛存在于包括人类在内的哺乳动物物种中的寄生虫。由于其形态不变，对宿主特异性和传播模式等方面的研究需要对来自宿主样本的囊肿/滋养体进行直接的基因特征分析。已经开发了许多分子检测方法来帮助揭示这种感染的复杂流行病学。这些研究得出了一个连贯的图景，表明存在七个基因群（或组合），其中两个（A和B）在人类和动物中都有发现，而其余五个（C - G）是宿主特异性的。基于序列的调查已经在动物物种的A和B组合中鉴定出了许多基因型，其中一些可能具有人畜共患病的潜力。然而，最近，分子方法因认识到分离株内的序列异质性（即“混合模板”，这会影响每个组合内亚型的鉴定）以及不同遗传标记对分离株归属十二指肠贾第虫组合的不可靠性而变得复杂。这引发了对先前基因分型数据解释的担忧，尤其是在使用单一遗传标记时。讨论了可能导致这些发现的机制，包括等位基因序列杂合性和减数分裂重组。
