Emergence of hemorrhagic septicemia caused by MLST type ST64 Pasteurella multocida in a European fallow deer population in Hungary.

A sudden mass mortality involving 44 fallow deer (Dama dama) occurred in September 2020 at a game management area near Budapest, Hungary. The die-off affected both sexes and all age classes equally. On postmortem examination of 2 subadults and 1 fawn, we found average body condition, diffuse subcutaneous edema, swelling of peripheral lymph nodes, marked hemorrhages in lymph nodes along the esophagus and trachea, and left ventricular dilation. We isolated Pasteurella-like colonies from spleen, liver, small intestine, lung, and brain samples of 7 animals, and identified them as P. multocida serotype B:2 by amplifying kmt1, toxA, and hyaC-hyaD genes, capsular typing by PCR, and serotyping by agar gel diffusion precipitation test, which established the diagnosis of hemorrhagic septicemia as the cause of the outbreak. By further analysis, we determined that all of our P. multocida isolates encoded ptfA, fimA, hsf-2, nanH, hgbA, and pfhA, but we did not detect genes encoding toxA, hsf-1, tbpA, or tadD. We identified our strains by RIRDC MLST as sequence type (ST)122, characteristic for strains causing hemorrhagic septicemia, while using multi-host MLST analysis we assigned these strains to ST64 clustering with P. multocida strains from the 2015 hemorrhagic septicemia outbreak of saiga antelopes in Kazakhstan. We concluded that increased population density and aggregation due to limited drinking water availability played a role in initiating the outbreak.