Serovars and SpaA Types of Erysipelothrix rhusiopathiae Isolated from Pigs in Japan from 2012 to 2019.

Erysipelothrix rhusiopathiae causes swine erysipelas (SE), which results in considerable economic loss on pig farms. During SE outbreaks that occurred sporadically from 2008 to 2011 in Japan, new E. rhusiopathiae strains were isolated with a specific surface protective antigen (Spa)A protein characterized by methionine at position 203 and isoleucine at position 257 (M203/I257 SpaA type). To determine whether strains with the M203/I257 SpaA type are still prevalent in Japan, we collected 79 strains of E. rhusiopathiae from pigs showing various SE symptoms from 2012 to 2019 and classified them based on serovar typing, spaA gene sequence analysis, and lineage typing. We found that the majority of recent E. rhusiopathiae strains (59/79) belonged to the serovar 1a strain, and that the M203/I257 SpaA type (56/59) was predominant continuing from 2008 to 2011. Furthermore, serovar 1a strains with IVb-1 and IVb-2 lineages that had been isolated in specific regions of Japan were no longer local but were found across Japan. The pathogenicity of recent isolates tested in mice was not significantly changed when compared to that of previously isolated strains. Our results suggest that recent SE outbreaks were not due to changes in the SpaA protein or to altered virulence of E. rhusiopathiae but were rather caused by the persistent presence of E. rhusiopathiae with the M203/I257 SpaA type.