Brucella ceti and brucellosis in cetaceans

Abstract

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.

Keywords: Brucella; Brucella ceti; brucellosis; cetacean; dolphin; marine brucellosis; porpoise; whale.

Figure 1

Continued Continued Cetacean phylogeny in relation to Brucella infections. The phylogenetic tree was constructed based in cytochrome B sequences as reported previously (May-Collado and Agnarsson, 2006). The species are named according to the current extant taxonomic rank. The color squares represent the different cetacean families as follows: Balaenopteridae + Eschrichtiidae (black), Neobalaenidae (light green), Balaenidae (red), Kogiidae + Physeteridae (purple), Ziphiidae (yellow), Platanistidae (light pink), Iniidae (pink), Pontoporiidae (green) Lipotidae (brown), Phocoenidae (gray) Monodontidae (light blue), and Delphinidae (blue). The acronyms used for locating the oceanic distribution are the following: Africa (Af), Amazon River (Azr), America (Am), Antarctic Ocean (An), Arabic Peninsula (Arp), Arctic Ocean (Ar), Atlantic (A), Austral Sea (Ats), Australia (Aus), Baja California Gulf (Bacg), Black Sea (Bs), Central (C), Central America (Ce), Chile (Ch), Continental (Co), East (E), Europe (Eu), Ganges River (Gar), Indian Ocean (In), Indochina Sea (Ich), Indus River (Inr), Japan (Ja), La Plata River (Lapr), Littoral (L), Madeira river (Mar), Magellan Strait (Ms), Mediterranean Sea (Mes), Mexico (Mx), New Zealand (Nz) North (N), Orinoco river (Orr), Pacific (P), Pe (Peru), South (S), West (W), Worldwide (World), and Yangtze river (Yr). Population: The acronyms for the cetacean population size correspond to: least concern (LC), threatened (T), conservation dependent (CD). The number of serologically positive cetaceans in a given test/total number of cetaceans tested is indicated as +/N°. The acronyms for the serological assays are: iELISA (I), cELISA-I (II), cELISA-II (III), aELISA (IV), gELISA (V), agELISA (VI), C’ELISA (VII), Western Blot (VIII), Dot Blot (IX), FPA (X), IF (XI), Complement fixation (XII), Rose Bengal agglutination (XIII), Card agglutination test (XIV), Rivanol agglutination (XV), 2-mercaptoethan agglutination (XVI), PCR (XVII). Under “Isolation” refers to Brucella isolated from tissues of cetaceans. The MLVA-16 corresponds to A1, A2, B, C1, and P1. The Brucella isolates not fully identified or only identified as B. ceti are indicated as Br and Bc, respectively. Serological and bacteriological data obtained from (Ewalt et al., ; Ross et al., ; Jepson et al., ; Clavareau et al., ; Miller et al., ; Tryland et al., ; Nielsen et al., ; Van Bressem et al., ; Foster et al., ; Sabin et al., ; Maratea et al., ; Marvulo et al., ; Ohishi et al., , ; Cowan, ; Duignan et al., ; Dawson et al., ; Omata et al., ; Tachibana et al., ; Alekseev et al., ; Manire et al., ; Hernández-Mora et al., , ; Jepson and Deaville, ; Neimanis et al., ; Cisterna et al., ; Davison et al., , ; Deaville and Jepson, ; Dove, ; Maquart et al., ; Uhart et al., ; Di Guardo et al., ; González-Barrientos et al., ; Jauniaux et al., ; Meegan et al., ; Hernández-Mora et al., unpublished). *Determined by PCR.

Figure 2

Cetaceans in the Pacific coast of Costa Rica. (A) Alive stranded striped dolphin (S. coeruleoalba) with neurobrucellosis, attended by local inhabitants. (B) Death stranded Cuvier’s beaked whale (Ziphius cavirostris) with positive Brucella serology in the shorelines where cattle (in the background) transits. (C) Alive striped dolphin (Stenella coeruleoalba) with neurobrucellosis being handled by tourists. (D) Dead stranded humpback whale (Megaptera novaeangliae; with permission, Grupo La Nación, Costa Rica).

Figure 3

Oceanic distribution of cetaceans with positive serological diagnosis for Brucella infections. References as in Figure 1.

Figure 4

Dispersion of Brucella species confronted to the phylogeny of their preferred host mammal. Phylogeny and time calibration of mammal evolution was adapted from (Kumar and Hedges, ; Bininda-Emonds et al., 2007). Brucella cladogram was estimated from MLVA-16 published values (http://minisatellites.u-psud.fr/MLVAnet/login.php?&largeur=1680). The dispersion of the various Brucella species is depicted as cones proportional to the number of strains analyzed. The numbers in the mammal phylogenetic tree represent million of years. The arrow indicates the proposed dispersion of the clade that gave origin to B. ceti strains. Notice that according to this proposal, the B. ceti B porpoise type is closer to the B. pinnipedialis C clusters than to the B. ceti dolphin types A1, A2, and P1. B. suis biovar 2 also has affinity for hares (lagomorphs).

Figure 5

Pathological findings in cetaceans with brucellosis. (A) Striped dolphin S. coeruleoalba fetus within placental presenting multiple necrotic foci diffusely distributed (arrow points a prominent focus); and, B. ceti detected by IF in impressions of placenta tissues (insert). (B) From (A) severe necrotizing placentitis showing detached placental cells (arrow) and marked necrosis of trophoblastic epithelial cells lining with infiltration of neutrophils into the fetal placental villi (HE stain 10×); and, I-HRP labeling of Brucella antigen within inflammatory cells invading the placental villi (insert). (C) Harbor porpoise P. phocoena right enlarged testicle (twofold) demonstrating an abscess and multi-locular lesions in the proximal area (arrow). From Dagleish et al., , with permission, license N° 2756120153946). (D) From (C) HE histological section of the affected testis showing necrosis (asterisk), thick fibrous capsule of the abscess (black arrows) and the foci of mononuclear inflammatory cells (blue arrows); and I-HRP labeling of Brucella inside macrophage like cells (arrows) in the testicular lesion (insert). From Dagleish et al., , with permission, license N° 2756120153946). (E) Vegetative nodule in the mitral valve (white arrow) of striped dolphin heart. (F) From (E) HE 10× histological section of the mitral valve showing bacterial colonies (arrow) intermixed within abundant fibrin deposits over the valve surface, focal areas of dystrophic calcification and severe suppurative inflammatory infiltrate surrounding this area. Insert shows positive I-HRP Brucella staining in inflammatory cells and bacterial aggregates (G) Hyperemic meningeal blood vessels in cerebral hemispheres and cerebellum from striped dolphin, showing cloudy and hemorrhagic cerebrospinal fluid in syringes. (H) Wright–Giemsa stained cells in cerebrospinal fluid from (G) composed of ependymal cells and mononuclear leukocytes. (I) IF of B. ceti and bacterial debris within phagocytic cells infiltrating cerebrospinal fluid shown in (H). (J) From (G) severe mononuclear inflammatory infiltrate in the meninges (black arrow) surrounding the spinal cord and hyperemic blood vessel (white arrow). (K) I-HRP labeling of Brucella antigens in cells that seem to be perivascular macrophages or pericytes laying below the endothelium of a vessel of the brain of striped dolphin (arrow), with no inflammatory response (courtesy of M. Barberán, Servicio de Investigación Agraria-DGA, Zaragoza, Spain). (L) I-HRP labeling of Brucella antigens in cells that seem to be macrophages or glial cells in the parenchyma of the brain of striped dolphin (courtesy of M. Barberán, Servicio de Investigación Agraria-DGA, Zaragoza, Spain). (M) Skulls (caudal view) and atlas bones (cranial surface view) of the affected Atlantic white-sided dolphin L. acutus (left) and the normal counterpart (right). The occipital condyles are completely absent in the affected animal (arrows), and only a roughened surface remains, which extends beyond the normal margins where these structures should be. There is also a lack of dorsal and lateral vertebral processes and normal smooth bone architecture, as well as a large amount of remodeling, present in the atlas bone. From Dagleish et al., , with permission, license N° 2756130134008).

Figure 6

Performance of protein G-HRP against odontocete sera and calibration of positive and negative controls. The performance of protein G-HRP in gELISA against sera from Brucella infected bovine (Bos taurus) and dolphin (S. coeruleoalba) was tested using two buffer conditions: PBS-Tween (pH 7.7) and 0.1 M acetate buffer (pH 5). The SE at all points was 5% of the values (from Hernández-Mora et al., , with permission).