Genomic epidemiology of Brucella suis biovar 2 in German swine and wildlife, 2003-2023

Falk Melzer^*Jörg LindeHanka Brangsch

• Institute of Bacterial Infections and Zoonoses, Friedrich Loeffler Institut, Jena, Germany

Porcine brucellosis, caused by Brucella suis biovar 2, is currently the only form of brucellosis in farm animals in Germany with officially reported outbreaks confirmed by direct pathogen detection. In most European countries, this bacterial pathogen is also found in wild animals, which are considered reservoirs. Since 2003, 22 porcine brucellosis outbreaks have been notified in Germany. A comprehensive study on German B. suis bv. 2 isolates obtained from routine diagnostic investigations of domestic pig, and wildlife was carried out. The dataset included isolates from 18 notified outbreaks. The aim was to assess epidemiological links and the genomic diversity of the bacterium. B. suis bv. 2 isolates were subjected to whole genome sequencing and analyzed using multilocus sequence typing (MLST), core genome MLST, and single nucleotide polymorphism (SNP) analysis. Three different MLST sequence types were identified and further subdivided into eight clusters. This approach conclusively confirmed officially reported primary and secondary outbreaks caused by the sale of infected animals. In individual cases, great similarities were found between domestic and wild animal isolates, i.e. differing by only 2 to 4 nucleotides. This similarity suggests brucellosis transmission events. Both wild boar and hare can be considered reservoirs of brucellosis. In Northern Germany, persistent B. suis bv. 2 foci were detected, as well as transmission across Germany and potentially to other European countries. Notably, hare isolates differed considerably from the majority of German wild boar and domestic pig isolates. As most brucellosis outbreaks occurred in outdoor holdings, reliable monitoring of these herds is recommended, although the exposure of these animals to external factors (e.g., vectors) poses a challenge. However, it is particularly important with regard to the increase in organic freerange and pasture farming, which promotes direct or indirect contact with wild animals.