Genomic insights into Salmonella Choleraesuis var. Kunzendorf outbreak reveal possible interspecies transmission.

Salmonella enterica serovar Choleraesuis is a host-adapted serovar that causes serious infections in domestic pigs and wild boars. Here, we investigated an outbreak of salmonellosis in domestic pigs in Slovenia, 2018-2019. To assess the outbreak, 18 isolates from domestic pigs, wild boars, wild boar meat and a human patient underwent whole-genome sequencing (WGS). All isolates were of sequence type (ST) 145 and harbored no antimicrobial resistance genes or AMR-associated mutations. A single transmission cluster (≤ 6 alleles) of spatially (< 100 km) and temporally linked isolates was observed, comprising isolates of pig (n = 9), wild boar (n = 2) and human (n = 1) origin, and suggesting possible interspecies transmission. In all outbreak-related animal cases, septicemic salmonellosis was observed, accompanied in some cases by enteric symptoms. All pig isolates were linked to a single intensive breeding farm that distributed growers to small family farms. The same transport vehicles were used to distribute growers to family farms and also to transport livestock between neighboring countries. Both isolates that originated from the imported wild boar meat were genetically distant (≥ 122 alleles) from the outbreak cluster. The present results indicate the importance of screening domestic pigs and proper disinfection of transport vehicles to control the spread of S. Choleraesuis.