Towards Integrated Surveillance of Marine Brucellosis: Diagnostic and Phylogenetic Assessment of Brucella ceti in Stranded Dolphins of the Western Mediterranean Sea

TL;DR

This study improves understanding of brucellosis in dolphins by analyzing infections and genetic diversity of Brucella ceti in the Western Mediterranean.

Contribution

The study introduces validated serological methods and identifies new genetic types of Brucella ceti in marine mammals.

Findings

Brucella ceti infection was confirmed in 46.7% of dolphins using bacteriological and molecular methods.

Two new sequence types (ST26 and ST49) of Brucella ceti were identified through whole-genome sequencing.

Striped dolphins showed particular susceptibility to Brucella ceti infection with neurological symptoms.

Abstract

Reports of brucellosis in free‐ranging cetaceans are increasing worldwide, particularly in the Mediterranean Sea. To enhance diagnostic accuracy and epidemiological understanding of cetacean brucellosis in the Western Mediterranean Sea, we analyzed bacteriological, serological, and molecular data from 30 cetaceans belonging to three different species stranded along the coast of the Valencian Community (Spain) between 2011 and 2021. Brucella ceti infection was confirmed by bacteriological isolation in 14 animals (46.7%) and by genus‐specific qPCR in 15 cases (50%), with some discrepancies between methods. When feasible, serological analyses were performed using a commercial blocking ELISA (bELISA) and/or the Rose Bengal agglutination test (RBT). In the absence of ELISA tests properly validated for its use in marine mammals, we assessed the optimum dilution and cut‐off of this ELISA kit using panels of gold‐standard sera from culture‐positive and brucellosis‐free dolphins. From a pathological perspective, 12 infected animals showed moderate to severe meningoencephalitis or meningoencephalomyelitis with lymphoplasmacytic infiltration. Additionally, whole‐genome sequencing (WGS) enabled the identification of two sequence types (STs), ST26 and ST49, indicating phylogenetic divergence. Our findings provide new insights into the phylogenetics of B. ceti and highlight the particular susceptibility of striped dolphins to this bacterium. The study also evidences the need for proper validation of the indirect diagnostic methods used for surveillance and seroepidemiological studies of brucellosis in marine mammals.

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