Histopathology of Cardiovascular Lesions in 17 Rough Toothed Dolphins (Steno bredanensis) Stranded in the Florida Panhandle During 1997, 1998, and 2001

The cardiovascular tissues of 17 rough toothed dolphins (Steno bredanensis) that mass stranded in the Florida panhandle during 1997, 1998 and 2001 were examined. Routine hematoxylin-eosin staining demonstrated the presence of extensive lesions in the cardiovascular systems of these stranded dolphins, such as myocarditis, arteritis, arteriosclerosis, cardiomyopathy and fibrosis. Histopathologic techniques were used to characterize these lesions, i.e. to locate the pathologic changes; to identify the cells and extracellular fibers involved; and to grade them according to their degree of severity. Masson trichrome, Movat pentachrome, Verhoeff elastic, and phosphotungstic acid hematoxylin stains were used to differentiate cells, collagen, elastin, and ground substance. Lesions were present in all animals, regardless of age or sex. The most common findings in the heart were fibrosis in 17 animals, myocarditis in 14, cardiomyopathy in 13 and fibroelastosis in nine animals. The aortas showed evidence of subintimal thickening in seven animals, inflammation in five, and thickening and degeneration of elastic fibers in three animals. Coronary arteries were affected by arteriosclerosis in seven animals, arteritis in seven, subintimal thickening in five, and muscle cell atrophy in four animals. The severity of the lesions was related to the presence of multiple pathological changes in the same animal. In females, the severity of the changes varied with age, with adult females demonstrating moderate to severe changes, while juvenile females had mild to moderate changes. In general, 25% (2/8) of the adult females had mild changes, 62.5% (5/8) had moderate changes, and 12.5% (1/8) had severe changes, while 67 % (2/3) of the juvenile females had mild changes and 33% (1/3) had moderate changes. In contrast, 50% (2/4; 1/2) of the adult and juvenile males had moderate changes and 50% (2/4; 1/2) of the adult and juvenile males had severe changes. Although the causes of these changes are unknown, they likely contributed to the cause of these mass strandings