Characterization of Renal Lesions Observed in Rough-Toothed Dolphins (Steno bredanensis) From a Mass Stranding at Cape San Blas, Florida, December 1997
IAAAM 1999
Amber Fort1; Ruth Ewing2; Gregory Bossart3
1Barry University, Miami Shores, FL, USA; 2National Marine Fisheries Service, Miami, FL, USA; 3University of Miami, School of Medicine, Division of Comparative Pathology, Miami, FL, USA


Sixty-two rough-toothed dolphins (Steno bredanensis) stranded alive on Cape San Blas in Gulf County, Florida on December 14, 1997. Although all of the animals returned to the sea initially, thirty-one restranded. Twelve animals died on the beach; three additional animals were euthanized. Sixteen were chosen for rehabilitation, ten of which died spontaneously, and two of which were euthanized over subsequent weeks. A total of twenty-seven dolphins were necropsied.

Renal lesions from twenty-four rough-toothed dolphins involved in this mass stranding were histologically examined and characterized, using standard hematoxylin and eosin (HE). Additional special histochemical stains were used to differentiate and better elucidate changes in key microscopic components.1,2,3,4 Lesions were characterized by interstitial fibrosis, medullary tubular mineralization, mesangial cell proliferation, basement membrane and Bowman's capsule thickening, and arterial medial degeneration and sclerosis. These histomorphologic criteria were then used to establish a grading scale such that a grade of zero had no changes or minimal scattered lesions and higher grades indicated increasing severity and distribution (Table 1).

Histopathologic results indicated a correlation between age and lesion severity, suggesting a chronic, progressive condition. Adult males presented with the most severe renal lesions in the stranded population, although adult females constituted a majority of the sample population. Possible differentials for a cause include a toxin, either a persistent organic pollutant and/or metal, infectious etiology or an age-related change, some of which are currently being investigated.

Table 1. Severity of renal lesions correlated with age and gender in twenty-four rough-toothed dolphins (Steno bredanensis).



Grade 0

Grade 1

Grade 2

Grade 3

Adult males




Adult females





Subadult males





Subadult females






4 2





The authors wish to thank Dr. Carolyn Cray and Brenda Roberts of the University of Miami for providing staining reagents and technical assistance, and the Southeast U.S. Stranding Network for contributing tissue samples for analysis, logistical support and tremendous effort in responding to this mass stranding.


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2.  Nakamura S, S Shibata, K Shirota, K Abe, K Uetsuka, H Nakayama, N Goto, K Doi. 1996. Renal Glomerular Fibrosis in a Cat. Vet. Pathol. 33:696-699.

3.  Dumbach DM, CA Smith, RM Lewis, TJ Van Winkle. 1997. Morphologic, Immunohistochemical, and Ultrastructural Characterization of a Distinctive Renal Lesion in Dogs Putatively Associated with Borrelia burgdorferi Infection. Vet. Pathol. 34:85-96.

4.  Koeman JP, WJ Biewenga, E Gruys. 1994. Proteinuria Associated with Glomerulosclerosis and Glomerular Collagen Formation in Three Newfoundland Dog Littermates. Vet. Pathol. 31:188-193.

Speaker Information
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Amber Fort
Barry University
Miami Shores, FL, USA

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