Genetic associations of “Brachyspira hampsonii” from diverse epidemiological origins and their relationships with other swine Brachyspira species

Outbreaks of bloody diarrhea in swine herds in the late 2000s signaled the re-emergence of swine dysentery in the U.S. Diagnostic investigations confirmed the emergence of a novel pathogen “Brachyspira hampsonii” with two distinct genetic groups circulating in U.S. swine. It has since been detected in swine and migratory birds in North America and Europe.

The aim of this study was to develop and implement a multilocus sequence typing (MLST) scheme in order to molecularly characterize “B. hampsonii” and to elucidate the diversity, distribution and genetic relationships of this pathogen from diverse epidemiological sources globally, as well as to evaluate the genetic relationships of “B. hampsonii” with other Brachyspira species.

Using our newly developed MLST scheme, we genetically characterized 81 “B. hampsonii” isolates originating from diverse epidemiological sources (different farms, swine systems, countries and host species).

A total of 20 genotypes known as sequence types (11 from the U.S. and nine from other countries) were identified. “B. hampsonii” exhibited a heterogeneous population structure with microevolution detected locally within swine production systems. Within the U.S., group I was widespread yet less diverse than group II. The clustering patterns displayed the association of genotypes and their country or swine system of origin. Isolates from migratory birds represented distinct yet closely related genotypes when compared with swine origin isolates. The comparative multilocus sequence analysis of 430 isolates representing pathogenic and commensal Brachyspira species from 19 countries and 10 host species depicted clustering by bacterial species. It revealed a close clustering of all “B. hampsonii” irrespective of their genetic group, thus providing support for both groups to be considered a single species. It also confirmed the close genetic relatedness of “B. hampsonii” with commensals B. murdochii and B. innocens, rather than other pathogens B. hyodysenteriae and “B. suanatina”.

This is the first study to establish a multilocus sequence typing scheme for “B. hampsonii”, to characterize its genotypes, and to elucidate its population structure. It highlights the role of MLST in routine surveillance/monitoring and the importance of strict biosecurity measures in preventing the spread of pathogens such as “B. hampsonii” between swine herds and also potentially between migratory birds and swine. It also suggests that “B. hampsonii” represents a diverse but single bacterial species that has close genetic associations with commensal Brachyspira species.

Disclosure of Interest: None Declared