Abstract
Outbreaks of mucohemorrhagic diarrhea in pigs caused by Brachyspira hyodysenteriae in the late 2000s indicated the re-emergence of Swine Dysentery (SD) in the U.S. Although the clinical disease was absent in the U.S. since the early 1990s, it continued to cause significant economic losses to other swine rearing countries worldwide. This study aims to fill the gap in knowledge pertaining to the re-emergence and epidemiology of B. hyodysenteriae in the U.S. and its global relationships using a multi-locus sequence typing (MLST) approach. Fifty-nine post re-emergent isolates originating from a variety of sources in the U.S. were characterized by MLST, analyzed for epidemiological relationships (within and between multiple sites of swine systems), and were compared with pre re-emergent isolates from the U.S. Information for an additional 272 global isolates from the MLST database was utilized for international comparisons. Thirteen nucleotide sequence types (STs) including a predominant genotype (ST93) were identified in the post re-emergent U.S. isolates; some of which showed genetic similarity to the pre re-emergent STs thereby suggesting its likely role in the re-emergence of SD. In the U.S., in general, no more than one ST was found on a site; multiple sites of a common system shared a ST; and STs found in the U.S. were distinct from those identified globally. Of the 110 STs characterized from ten countries, only two were found in more than one country. The U.S. and global populations, identified as clonal and heterogeneous based on STs, showed close relatedness based on amino acid types (AATs). One predicted founder type (AAT9) and multiple predicted subgroup founder types identified for both the U.S. and the global population indicate the potential microevolution of this pathogen. This study elucidates the strain diversity and microevolution of B. hyodysenteriae, and highlights the utility of MLST for epidemiological and surveillance studies.
Highlights
Swine dysentery (SD) is a mucohemorrhagic diarrheal disease of pigs caused by an anaerobic spirochete, Brachyspira hyodysenteriae [1]
Two contemporary U.S isolates were characterized as ST56, the same sequence types (STs) as that of the historic ATCC type strain B78T (ATCC 27164) which originated from the U.S in the 1970s
This study analyzed the epidemiology of B. hyodysenteriae isolates from North America and their relationships with global isolates over the last five decades
Summary
Swine dysentery (SD) is a mucohemorrhagic diarrheal disease of pigs caused by an anaerobic spirochete, Brachyspira hyodysenteriae [1]. Despite the economic importance of the disease in the U.S, no information currently exists on the epidemiology of this important pathogen within the U.S, or on the potential relatedness of these post re-emergent isolates (after the late 2000s) with those present in the U.S pre re-emergence (before the early 1990s). Phenotypic features such as virulence [4] and antimicrobial susceptibility [5] vary in different strains and may play a role in this re-emergence, highlighting the importance of strain characterization
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