Abstract

Cardiac disease is an important cause of mortality for southern sea otters in California. This condition was newly described and had no known etiology in beachcast sea otters necropsied from 1998 and 2001 at the California Department of Fish and Game’s Marine Wildlife Veterinary Care and Research Center. The objectives of this study were to characterize cardiac lesions observed in southern sea otters and evaluate common sea otter pathogens and potential infectious, toxic and nutritional etiologies for their relationship with cardiac disease. Characterization of cardiac lesions by gross and microscopic necropsy findings has allowed the definition of two overlapping cardiac disease syndromes in otters: (1) myocarditis, characterized by lymphocytic inflammation of myocardium and (2) dilated cardiomyopathy (DCM), characterized by grossly enlarged atria and ventricles with concurrent myocarditis. Major risk factors associated with myocarditis included adult age, good body condition (likely as a result of an acute death), exposure to Sarcocystis neurona, and suspected exposure to domoic acid. Domoic acid, a marine toxin produced by Pseudo-nitzschia australis, is a common cause of mortality in sea lions and causes characteristic clinical signs involving the central nervous system. While there may be other factors associated with myocarditis that were not evaluated here, these findings suggest that S. neurona and domoic acid may both be important causes of myocarditis in sea otters. Myocarditis associated with exposure to S. neurona occurred predominantly in the northern part of the sea otter range, while domoic acid-related myocarditis occurred largely in the south, where domoic acid blooms were more frequent. A spatio-temporal cluster of DCM was identified in the southern aspect of the sea otter range in California from May to November 2000. Adult age and suspected previous exposure to domoic acid were associated with an increased risk of DCM. Also, otters with DCM had significantly lower concentrations of myocardial L-carnitine than controls and otters with myocarditis. Dilated cardiomyopathy may be an advanced stage of domoic acid-induced myocarditis in sea otters, possibly following chronic and repeated exposures to domoic acid blooms. While the relationship between domoic acid and myocardial L-carnitine concentrations requires further research, myocardial L-carnitine might play a key role in the progression of myocarditis to DCM in sea otters.