The genomic landscape of Pasteurella multocida B:2 causing haemorrhagic septicaemia in Germany

Haemorrhagic septicaemia (HS) is a peracute to acute, highly fatal disease caused by Pasteurella ( P. ) multocida serogroups B:2 and E:2 affecting cattle and buffaloes. HS in cattle and buffaloes necessitates mandatory reporting to the World Organisation for Animal Health (WOAH; formerly OIE) due to its significant socio-economic impact on livestock production and international trade. In other ungulate species infection with P. multocida B:2 (iPmB:2) presents with a similar clinical picture. A series of HS and iPmB:2 outbreaks between 2010 and 2024 in Germany required a detailed investigation into the spatiotemporal dynamics and molecular characteristics of the circulating strains. The ability to specifically identify and analyse circulating serovars is crucial for confirming outbreaks and implementing appropriate control measures. A total of 221 Pasteurella multocida capsular type B:2 isolates associated with HS/iPmB:2 outbreaks was collected between 2010 and 2024 from dead livestock and wildlife in Germany in the context of veterinary practice and subsequently analysed using whole-genome sequencing. Isolates were characterised by capsular and lipopolysaccharide PCR-based typing, multilocus sequence typing, and high-resolution genomic comparison. Four high-resolution-typing approaches were evaluated and compared with epidemiologically defined outbreaks to identify the most suitable method for outbreak investigation. Single nucleotide polymorphism (SNP)-based analysis showed the highest discriminatory power and best agreement with known outbreak data, outperforming conventional multilocus sequence typing (MLST) and core-genome multilocus sequence typing (cgMLST) approaches. Genotyping identified eight major genetic clusters of closely related strains across multiple federal states and host species. Several outbreaks were linked by highly similar or identical genomes, suggesting both local persistence and wider geographic spread of the pathogen within Germany.