Abstract

During the years 1992 through 2009, 19 of 84 (23%) code 2 beach-stranded Atlantic bottlenose dolphins, Tursiops truncatus examined by necropsy, were found to have meningitis, with varying degrees of obstructive hydrocephalus. Cases were widely distributed along the Texas coast, approximating the distribution of non-meningitis related strandings. There was no particular seasonal distribution. Of the 19 animals, 10 were either freshly dead or died during rescue, and 9 survived stranding long enough for clinical observations. Survival ranged from less than a day to 314 days. One survived 59 days, and two for more than 100 days. These long-term survivors had a long period in which they were clinically normal, before displaying abnormal behavior, ending in death.

Two distinct patterns of inflammation were recognized; fibrinopurulent (2), one associated with Edwardsiella tarda, one with Vibrio alginolyticus and Staphylococcus sp., the remainder granulomatous. The fibrinopurulent exudate was mainly distributed on the vertex of the brain, while the granulomatous reaction was prominent at the base of the brains. Brucella sp. was cultured from one case of granulomatous meningitis. Retrospective study of all granulomatous meningitis cases revealed no differentiating histological differences between the case with culturable Brucella and those without. Inability to culture Brucella might relate to treatment with antibiotics, overgrowth of cultures by contaminants, or, especially in early years of this study, lack of suspicion about the presence of slow-growing Brucella, and premature discard of apparently negative cultures.

Striking features of the granulomatous meningitis cases were vasculitis and proliferative fibrosis of the meninges, resulting in obstruction to flow of cerebrospinal fluid at the base of the brain, with subsequent hydrocephalus interna. This feature of hydrocephalus interna complicating pneumococcal meningitis and tuberculous meningitis, both diseases characterized by pronounced basal exudates, is well recognized in human medicine. Organization of the exudates is inevitable and inexorable.

These cases illustrate the high frequency of granulomatous meningitis in the free-ranging population of bottlenose dolphins in the western Gulf of Mexico, and suggest that further study may reveal Brucella sp. to be a common cause. They also indicate the importance of early screening of live beach-stranded dolphins for Brucella infection, so that scarce resources are not expended in an inevitably futile attempt at rehabilitation.

Acknowledgments

Grateful thanks are offered to the volunteers of the Texas Marine Mammal Stranding Network, without whom no study would have been possible, and to the Clinical Microbiology Laboratory of the University of Texas Medical Branch. Identification of Brucella was confirmed by the USDA Laboratory, Ames, Iowa.