Abstract

In recent years the most common species of cetacean that has stranded in Costa Rica is the striped dolphin (Stenella coeruleoalba). The histopathological findings in most of these cases suggest pathologies related to the central nervous system including meningoencephalitis. Classical agents have been investigated to determine the cause of the pathology, such as morbillivirus, however all of these tests were negative. From three dolphins, Brucella spp. was isolated from cerebrospinal fluid and different organs of the reticuloendothelial system. Members of the Brucella genus, tentatively assigned as "Brucella cetaceae", are known pathogens of porpoises, dolphins and whales.¹ Clinical experiences and knowledge of the pathobiology of this microorganism are limited; however, there are descriptions of reproductive² and neurological disorders^3,4 that may cause the animal's death. It is likely that the invasion by these intracellular bacteria in the CNS in dolphins causes the meningoencephalitis and causes the stranding due to development of symptoms such as inability to maintain buoyancy, opisthotonus, tremors, and seizures. This invasive behavior of Brucella spp. suggests that the striped dolphin may be a secondary (accidental) host.

Due the limited diagnostic tools for this disease in cetaceans, we developed and standardized an indirect ELISA with high chemical and serological sensitivity, and specificity, for the detection of antibodies against Brucella in odontocetes. Moreover, this test is simple and has predictive value for the isolation of Brucella spp. The assay is based on the detection of antibodies against Brucella lipopolysaccharide and development with a specific conjugate against odontocete IgG's.

According to the statistical analysis performed on 147 sera (138 from Mote Marine Laboratory, Florida, nine from Costa Rica), a sensitivity of 93.75%, a specificity of a 97.06%, and a kappa value of 0.9 were obtained, when the indirect ELISA was compared to both indirect immunofluorescence and Rose Bengala tests. From a total of 99 odontocetes from 16 different species from Florida, 27 (27%) were positive on the assay, regardless of age, sex or reproductive status. Nine odontocetes from the Pacific coast of Costa Rica were tested and seven were ELISA positive (78%) and Brucella spp. was isolated from three of them. From both areas, twelve out of fifteen meningoencephalitis cases (80%) showed high titers of antibodies against Brucella.

Although there is no epidemiological description for this disease in cetaceans, but this work suggests that infections with this bacteria in natural conditions is important and should be considered as a differential diagnosis, especially in an animal showing nervous symptoms. The zoonotic risk from Brucella infected dolphins must also be considered when working with cetaceans with neurological symptoms.

References

1.  López-Goñi I, I Morriyón. 2004. Brucella molecular and cellular biology: DNA polymorphism and taxonomy of Brucella species. 1st. ed. Horizon Bioscience, England.

2.  Miller WG, LG Adams, TA Ficht, NF Cheville, JP Payeur, DR Harley, C House, SH Ridgway. 1999. Brucella-induced abortions and infection in bottlenose dolphins (Tursiops truncatus). J. Zoo. Wildl. Med. 30: 100-110

3.  González L, IA Patterson, RJ Reid, G Foster, M Barberán, JM Blasco, S Kennedy, FE Howie, J Godfroid, AP MacMillan, A Schock, D Buxton. 2002. Chronic meningoencephalitis associated with Brucella sp. infection in live-stranded striped dolphins (Stenella coeruleoalba). J. Comp. Pathol. 126: 147-152.

4.  Muñoz PM, G García-Castrillo, P López-García, JC González-Cueli, MJ De Miguel, CM Marín, M Barberán, JM Blasco. 2006. Isolation of Brucella species from a live-stranded striped dolphin (Stenella coeruleoalba) in Spain. Vet. Rec. 158: 450-451.