Dissemination of Clonal Groups of Brachyspira hyodysenteriae amongst Pig Farms in Spain, and Their Relationships to Isolates from Other Countries

BackgroundSwine dysentery (SD) is a widespread diarrhoeal disease of pigs caused by infection of the large intestine with the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. Understanding the dynamics of SD, and hence being able to develop more effective measures to counter its spread, depends on the ability to characterise B. hyodysenteriae variants and trace relationships of epidemic strains. Methodology/Principal FindingsA collection of 51 Spanish and 1 Portuguese B. hyodysenteriae isolates was examined using a multilocus sequence typing (MLST) scheme based on the sequences of seven conserved genomic loci. The isolates were allocated to 10 sequence types (STs) in three major groups of descent. Isolates in four of the STs were widely distributed in farms around Spain. One farm was infected with isolates from more than one ST. Sequence data obtained from PubMLST for 111 other B. hyodysenteriae strains from other countries then were included in the analysis. Two of the predominant STs that were found in Spain also were present in other European countries. The 73 STs were arranged in eleven clonal complexes (Cc) containing between 2 and 26 isolates. A population snapshot based on amino acid types (AATs) placed 75% of the isolates from 32 of the 48 AATs into one major cluster. The founder type AAT9 included 22 isolates from 10 STs that were recovered in Spain, Australia, Sweden, Germany, Belgium, the UK, Canada, and the USA. Conclusions/SignificanceThis MLST scheme provided sufficient resolution power to unambiguously characterise B. hyodysenteriae isolates, and can be recommended as a routine typing tool that rapidly enables comparisons of isolates. Using this method it was shown that some of the main genetic lineages of B. hyodysenteriae in Spain also occurred in other countries, providing further evidence for international transmission. Finally, analysis of AATs appeared useful for deducing putative ancestral relationships between strains.

背景
猪痢疾（Swine dysentery, SD）是一种广泛流行的猪腹泻性疾病，由厌氧肠道螺旋体猪痢疾短螺旋体（Brachyspira hyodysenteriae）感染大肠引发。解析猪痢疾的流行动态，进而制定更有效的传播防控措施，有赖于对猪痢疾短螺旋体变异株进行精准分型，并追溯流行菌株间亲缘关系的能力。

研究方法与主要结果
本研究基于7个保守基因组位点的序列，采用多位点序列分型（multilocus sequence typing, MLST）方案，对51株西班牙源与1株葡萄牙源的猪痢疾短螺旋体分离株开展分型分析。结果显示，这些分离株可被划分为10个序列型（sequence types, STs），隶属于3个主要进化分支；其中4个序列型的分离株在西班牙各养殖场中广泛分布，且存在1个养殖场同时感染多种序列型分离株的情况。
随后，我们将从PubMLST数据库获取的其余111株来自不同国家的猪痢疾短螺旋体菌株序列数据纳入分析。在西班牙检出的2种优势序列型，同样存在于其他欧洲国家。本次分析共涉及73个序列型，被划分为11个克隆群（clonal complexes, Cc），每个克隆群包含2至26株分离株。基于氨基酸型（amino acid types, AATs）构建的种群快照显示，48个氨基酸型中的32个所对应的75%分离株聚集于一个主要聚类簇中；祖先型AAT9包含了来自10个序列型的22株分离株，这些分离株分别采自西班牙、澳大利亚、瑞典、德国、比利时、英国、加拿大及美国。

结论与意义
该多位点序列分型方案具备足够的分辨能力，可对猪痢疾短螺旋体分离株进行明确分型，可作为常规分型工具用于快速开展分离株间的比较分析。通过该方法证实，西班牙境内猪痢疾短螺旋体的部分主要遗传谱系同样存在于其他国家，为其跨国传播提供了进一步的证据。此外，氨基酸型分析可有效推断菌株间推测的祖先亲缘关系。