Abortion and Lethal Septicaemia in Sows Caused by a Non-ST194 Streptococcus equi subsp. zooepidemicus

Outbreaks of zoonotic Streptococcus equi subsp. zooepidemicus (SEZ) have caused severe epidemics in the pig sector since the 1970s in Southeastern Asia, China, and more recently North America. Cases of high mortality caused by peracute septicaemia were all attributed to strains of a highly virulent clonal lineage belonging to the sequence type (ST) 194. In Europe, only two outbreaks have been reported with similar features, caused by other sequence types. In August 2023, a febrile disease followed by abortion and subsequent death was observed among sows kept in a small-scale organic pig farm in West Hungary. Symptoms, pathological lesions, and microbiological findings were suggestive of septicaemia from bacterial origin caused by SEZ. According to the results of the routine laboratory testing, no other relevant infectious agents were involved. Whole-genome sequence analysis assigned the examined strains to ST138, unrelated to any of the European isolates. It also revealed a few common SEZ virulence genes, compared to the highly virulent ST194 strains. A sudden weather change and subsequent extremely high average daily temperature before the outbreak could be identified as the only predisposing factor. The immediate antibiotic treatment and applied biosecurity measures might have helped to restrict and terminate the outbreak. To our knowledge, this is the first report on abortion and lethal septicaemia in sows from Central and Eastern Europe. The results call attention to the potential of non-ST194 SEZ strains to cause outbreaks in pig farms.