Abstract
Brucella ceti infections have been increasingly reported in cetaceans, although a limited characterization of Mediterranean Brucella spp. isolates has been previously reported. We focused on 23 cases of B. ceti infection occurred in striped dolphins stranded along the Italian coastline from 2012 to 2021, investigated by the network of Istituti Zooprofilattici Sperimentali laboratories, coordinated by the National Reference Centre for Diagnostic Investigations on Stranded Marine Mammals (C.Re.Di.Ma.). We assessed the gross and microscopic findings, the results of microbiological, biomolecular and serological investigations, as well as the detection of other relevant pathogens, and the results of whole genomic sequencing and comparative genomic analysis. Pathological changes consistent with B. ceti infection were detected in the central nervous system of 19 animals, showing non-suppurative meningoencephalitis; 5 of which showed B. ceti-associatedpathological findings also in other tissues. In 6 cases severe coinfections were detected, mostly involving Dolphin Morbillivirus (DMV). We classified the 23 isolates into two sequence types, the ST26, prevalent, and the ST49. Whole genome SNP analysis showed that strains from Italy clustered into five genetically distinct clades. Plotting these clades onto the geographic map suggests a link between their phylogeny and topographical distribution (Adriatic Sea, Ionian Sea, Ligurian Sea, Sardinian Sea, Tyrrhenian Sea) alongside a potential indication of separation of the circulating striped dolphins. These results represent an exhaustive characterization of B. ceti isolated from Italian waters and show the usefulness of WGS for understanding of the evolution of this emerging pathogen. The severity of B. ceti-associated lesions reported herein confirms the role of this microbial agent as a primary neurotropic pathogen in striped dolphins, as well as a probable cause of stranding events and death, as previously described. Moreover, our findings highlight the importance of a multidisciplinary approach in the monitoring of stranded cetaceans, with epidemiological data and laboratory informations truly shared across sectors in a One Health-based perspective.
