Since the first case of brucellosis detected in a dolphin aborted fetus, an increasing number of Brucella ceti isolates has been reported in members of the two suborders of cetaceans: Mysticeti and Odontoceti. Serological surveys have shown that cetacean brucellosis may be distributed worldwide in the oceans. Although all B. ceti isolates have been included within the same species, three different groups have been recognized according to their preferred host, bacteriological properties, and distinct genetic traits: B. ceti dolphin type, B. ceti porpoise type, and B. ceti human type. It seems that B. ceti porpoise type is more closely related to B. ceti human isolates and B. pinnipedialis group, while B. ceti dolphin type seems ancestral to them. Based on comparative phylogenetic analysis, it is feasible that the B. ceti ancestor radiated in a terrestrial artiodactyl host close to the Raoellidae family about 58 million years ago. The more likely mode of transmission of B. ceti seems to be through sexual intercourse, maternal feeding, aborted fetuses, placental tissues, vertical transmission from mother to the fetus or through fish or helminth reservoirs. The B. ceti dolphin and porpoise types seem to display variable virulence in land animal models and low infectivity for humans. However, brucellosis in some dolphins and porpoises has been demonstrated to be a severe chronic disease, displaying significant clinical and pathological signs related to abortions, male infertility, neurobrucellosis, cardiopathies, bone and skin lesions, strandings, and death.

Seventeen striped dolphins (Stenella coeruleoalba) displaying swimming disorders compatible with neurological syndromes were investigated for Brucella infection. Sixteen dolphins had meningoencephalomyelitis. Serum antibody against Brucella antigen was detected in all 14 animals tested and Brucella ceti was isolated from eight out of nine animals. Brucella antigen was detected in the brain by immunofluorescence, but not by immunohistochemical labelling. By contrast, Brucella antigen was demonstrated by immunohistochemistry in the trophoblast of animals with severe placentitis and in the mitral valve of animals with myocarditis. The microscopical lesions observed in the tissues of the infected dolphins were similar to those of chronic brucellosis in man. The severity of brucellosis in S. coeruleoalba indicates that this dolphin species is highly susceptible to infection by B. ceti.

Ten striped dolphins, Stenella coeruleoalba, stranded along the Costa Rican Pacifi c coast, had meningoencephalitis and antibodies against Brucella spp. Brucella ceti was isolated from cerebrospinal fl uid of 6 dolphins and 1 fetus. S. coeruleoalba constitutes a highly susceptible host and a potential reservoir for B. ceti transmission. Brucellosis is a zoonotic disease of terrestrial and marine mammals. During the past 3 decades, contacts between cetaceans and humans have increased worldwide (1), augmenting the risk for transmission of pathogenic Brucella spp. from these animals to people (2). Indeed, Brucella marine strains are capable of infecting humans and livestock (3,4). The StudyFrom August 2004 through April 2007, 10 live striped dolphins, Stenella coeruleoalba (3 female adults, 2 female juveniles, 1 female calf, 4 juvenile males), were found stranded in populated areas at the Pacifi c shoreline of the Puntarenas Province of Costa Rica. All animals had swimming problems compatible with neurologic disorders and died within 48 hours of being found. Corpses were kept on ice and transported to the Pathology Unit, Veterinary School, National University, Costa Rica, for sampling; necropsy; and histopathologic, immunohistochemical, and serologic studies. With exception of 1 dwarf sperm whale, Kogia sima, these 10 dolphins were the only cetaceans we were able to examine during this 32-month period.Because marine Brucella spp. have been reported to cause intracerebral infections (3), we decided to perform immunohistochemical and serologic tests. For these tests, rabbit immunoglobulin (Ig) G anti-B. abortus lipopolysaccharide (LPS) was produced and isolated as described elsewhere (5). Antibodies against dolphin Steno bredanensis IgG were produced in rabbits, purifi ed according to described protocols (6). Both rabbit antibodies were linked to fl uorescein isothiocyanate and peroxidase and were assayed by using immunofl uorescent and Western blot techniques, respectively (5,7). Rose Bengal agglutination test, immunofl uorescent assays, and competitive ELISA were designed and used as described (8,9).Blood was collected from the live dolphins in situ, serum was obtained, and physical and chemical examinations were performed, followed after death by necropsies and gross pathologic and histopathologic studies. Tissues were fi xed in formalin, embedded in paraffi n wax, sectioned, and stained with hematoxylin and eosin (10). Organs and tissues of 5 adult females and 1 juvenile male were analyzed for bacteria (11); however, no samples for bacteriologic studies were available from the other dolphins that were stranded before July 2006. Identifi cation of the bacterial isolates was performed according to standard protocols (11,12). Fresh tissue impressions or pellets from supernatants of macerated tissues were fi xed with cold 3% paraformaldehyde for 15 min on ice and subjected to immunofl uorescence for detection of Brucella spp. (9). Genotyping of Brucella isolates was performed by PCR, using 5′-GGCTGATCTCGCAAAGAT-3′ an...

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Intracellular bacterial pathogens probably arose when their ancestor adapted from a free-living environment to an intracellular one, leading to clonal bacteria with smaller genomes and less sources of genetic plasticity. Still, this plasticity is needed to respond to the challenges posed by the host. Members of the Brucella genus are facultative-extracellular intracellular bacteria responsible for causing brucellosis in a variety of mammals. The various species keep different host preferences, virulence, and zoonotic potential despite having 97–99% similarity at genome level. Here, we describe elements of genetic variation in Brucella ceti isolated from wildlife dolphins inhabiting the Pacific Ocean and the Mediterranean Sea. Comparison with isolates obtained from marine mammals from the Atlantic Ocean and the broader Brucella genus showed distinctive traits according to oceanic distribution and preferred host. Marine mammal isolates display genetic variability, represented by an important number of IS711 elements as well as specific IS711 and SNPs genomic distribution clustering patterns. Extensive pseudogenization was found among isolates from marine mammals as compared with terrestrial ones, causing degradation in pathways related to energy, transport of metabolites, and regulation/transcription. Brucella ceti isolates infecting particularly dolphin hosts, showed further degradation of metabolite transport pathways as well as pathways related to cell wall/membrane/envelope biogenesis and motility. Thus, gene loss through pseudogenization is a source of genetic variation in Brucella, which in turn, relates to adaptation to different hosts. This is relevant to understand the natural history of bacterial diseases, their zoonotic potential, and the impact of human interventions such as domestication.