Emergence of the zoonotic bacterium Necropsobacter rosorum in nutria Myocastor coypus with implications for wildlife and human health.

The nutria (Myocastor coypus), a semi-aquatic rodent native to South America, poses significant ecological and agricultural threats as an invasive species in France, where it continues to proliferate despite sustained control efforts. A fatal case of pneumonia in a nutria from Marseille (France) prompted a microbiological investigation that led to the isolation, taxonomic classification, genomic characterization, and phylogenetic analysis of Necropsobacter rosorum. Whole-genome sequencing of the N. rosorum strain RG01 revealed a genome size of 2,505,657 base pairs and 2303 predicted open reading frames, showing high similarity to other publicly available N. rosorum genomes. Comparative pan-genomic analysis indicated a high level of genomic conservation among N. rosorum strains. The presence of putative virulence factors and a CRISPR-Cas system suggests both pathogenic potential and adaptive defense mechanisms against bacteriophage predation. This study also explored the genetic epidemiology of members of the Pasteurellaceae family, highlighting a considerable overlap between species infecting animals and humans. Among the 408,387 sequence records retrieved from GenBank, 62.1% were deemed suitable for genomic epidemiological analysis. Notably, N. rosorum was underrepresented, with only 13 entries spanning nine countries and three host types, revealing critical gaps in current surveillance and research. Collectively, these findings contribute to a better understanding of the microbiology and epidemiology of N. rosorum and Pasteurellaceae-associated infections, and underscore the importance of integrated, genomics-informed approaches for the monitoring, control, and prevention of zoonotic diseases.