Laboratory for Zoonoses and Environmental Microbiology, National Institute for Public Health and Environment (RIVM), Bilthoven, The Netherlands.
PLoS Negl Trop Dis. 2009 Dec 1;3(12):e558. doi: 10.1371/journal.pntd.0000558.
Giardia duodenalis, originally regarded as a commensal organism, is the etiologic agent of giardiasis, a gastrointestinal disease of humans and animals. Giardiasis causes major public and veterinary health concerns worldwide. Transmission is either direct, through the faecal-oral route, or indirect, through ingestion of contaminated water or food. Genetic characterization of G. duodenalis isolates has revealed the existence of seven groups (assemblages A to G) which differ in their host distribution. Assemblages A and B are found in humans and in many other mammals, but the role of animals in the epidemiology of human infection is still unclear, despite the fact that the zoonotic potential of Giardia was recognised by the WHO some 30 years ago. Here, we performed an extensive genetic characterization of 978 human and 1440 animal isolates, which together comprise 3886 sequences from 4 genetic loci. The data were assembled into a molecular epidemiological database developed by a European network of public and veterinary health Institutions. Genotyping was performed at different levels of resolution (single and multiple loci on the same dataset). The zoonotic potential of both assemblages A and B is evident when studied at the level of assemblages, sub-assemblages, and even at each single locus. However, when genotypes are defined using a multi-locus sequence typing scheme, only 2 multi-locus genotypes (MLG) of assemblage A and none of assemblage B appear to have a zoonotic potential. Surprisingly, mixtures of genotypes in individual isolates were repeatedly observed. Possible explanations are the uptake of genetically different Giardia cysts by a host, or subsequent infection of an already infected host, likely without overt symptoms, with a different Giardia species, which may cause disease. Other explanations for mixed genotypes, particularly for assemblage B, are substantial allelic sequence heterogeneity and/or genetic recombination. Although the zoonotic potential of G. duodenalis is evident, evidence on the contribution and frequency is (still) lacking. This newly developed molecular database has the potential to tackle intricate epidemiological questions concerning protozoan diseases.
蓝氏贾第鞭毛虫最初被认为是一种共生生物，是人类和动物贾第虫病的病原体。贾第虫病在全球范围内引起重大的公共和兽医健康问题。传播途径要么是直接的，通过粪-口途径，要么是间接的，通过摄入受污染的水或食物。对蓝氏贾第鞭毛虫分离株的基因特征分析揭示了存在 7 个组（A 至 G 组），它们在宿主分布上有所不同。A 组和 B 组存在于人类和许多其他哺乳动物中，但动物在人类感染流行病学中的作用仍不清楚，尽管 30 年前世界卫生组织就已经认识到贾第虫的人畜共患潜力。在这里，我们对 978 个人类和 1440 个动物分离株进行了广泛的遗传特征分析，这些分离株共包含 3886 个来自 4 个遗传基因座的序列。这些数据被组合到一个由公共和兽医健康机构的欧洲网络开发的分子流行病学数据库中。在不同的分辨率水平（同一数据集上的单个和多个基因座）进行基因分型。在研究组、亚组甚至每个单个基因座时，A 组和 B 组的人畜共患潜力都很明显。然而，当使用多基因座序列分型方案定义基因型时，只有 2 种 A 组多基因座基因型（MLG）和 B 组没有一种具有人畜共患潜力。令人惊讶的是，在单个分离株中反复观察到基因型的混合物。可能的解释是宿主摄取了遗传上不同的贾第虫包囊，或者随后感染了已经感染的宿主，可能没有明显的症状，感染了不同的贾第虫物种，这可能导致疾病。对于混合基因型的其他解释，特别是对于 B 组，可能是等位基因序列异质性和/或遗传重组。尽管蓝氏贾第鞭毛虫的人畜共患潜力是显而易见的，但关于其贡献和频率的证据（仍然）缺乏。这个新开发的分子数据库有可能解决关于原生动物疾病的复杂流行病学问题。
