XANTHINE NEPHROLITHIASIS IN JUVENILE CAPTIVE GIANT OTTERS (PTERONURA BRASILIENSIS).

Nephrolithiasis has been reported in several aquatic mammals including bottlenose dolphins (Tursiops truncatus), small clawed otters (Amblonyx cinereus), European river otters (Lutra lutra), North American river otters (Lontra canadensis), northern elephant seals (Mirounga angustirostris), Florida manatees (Trichechus manatus latirostris), and California sea lions (Zalophus californianus). Compositions of calculi in previous cases were predominantly calcium oxalate or ammonium acid urate. Xanthine urolithiasis is rare in veterinary medicine. Primary cases (without exposure to xanthine dehydrogenase inhibitors) occur as a consequence of hereditary xanthinuria, although the causal mutation has only been discovered in a subset of cases. Five captive juvenile giant otters (Pteronura brasiliensis) from two facilities were diagnosed with nephrolithiasis: three siblings from one set of parents and two siblings from another pair. Serum analyte assays revealed renal compromise in affected individuals. Computed tomography (CT) confirmed the presence of nephrolithiasis in one individual. Postmortem evaluation identified extensive bilateral nephrolithiasis on gross necropsy in four of five cases. Calculus analyses identified 100% xanthine composition. Histologic examination revealed marked nephrolithiasis with associated tubular necrosis and gastric mineralization. Nutrient composition of the diet including mineral and purine content was assessed. No association between diet and nephroliths was found in this study. This is the first report of xanthine nephrolithiasis in aquatic mammals. The potential role of diet and genetics in xanthine nephrolithiasis in the small inbred population of giant otters under human care needs further investigation to assess the implications of this disease process for the long-term captive management of this species.