OCCURRENCE OF RENAL AND VAGINAL CALCULI IN STRANDED CETACEANS ON CAPE COD AND IN SOUTHEASTERN MASSACHUSETTS, USA, 2006–23

Nephrolithiasis in cetaceans has been documented primarily in managed populations of bottlenose dolphins (Tursiops truncatus) with few described cases of nephroliths and vaginoliths in free-ranging cetacean species. Between 2006 and 2023, renal and/or vaginal calculi were identified on necropsy in 16 cetaceans that stranded on Cape Cod and in southeastern Massachusetts, USA. All vaginoliths (n=4) and most nephroliths were observed in short-beaked common dolphins (Delphinus delphis; n=9). Singular nephrolithiasis cases were also identified in a harbor porpoise (Phocoena phocoena), fin whale (Balaenoptera physalus), humpback whale (Megaptera novaeangliae), and long-finned pilot whale (Globicephala melas). Numbers of nephroliths in each animal ranged from 1 to >100 and nephrolith diameter ranged from 1 mm to 2.5 cm. Nephroliths were predominantly composed of: 100% ammonium urate in common dolphins (8/9 cases), 100% calcium phosphate carbonate in the fin and humpback whales, and 100% calcium oxalate dihydrate in the pilot whale; nephroliths were unavailable for analysis in the porpoise. Vaginoliths were predominantly composed of struvite but also contained lesser percentages of calcium carbonate and ammonium urate. None of the cases with antemortem blood analysis (n=7) had elevated renal parameters; however, two common dolphins had significant nephrolith-associated renal inflammation identified histologically, one of which also had bacterial pyelonephritis. Most nephroliths appeared to be incidental to the stranding; however, nephrolithiasis cases documented in common dolphins have increased over the past decade without significant change in necropsy protocols. No nephrolithiasis cases were documented in common dolphins 2006-16 (0/147), but starting in 2017, there was at least one documented case per year (9/103, 8.7%). To continue monitoring this potentially emerging trend, clinical and necropsy examinations of stranded cetaceans, especially in the western North Atlantic, should carefully evaluate for evidence of the condition, its potential clinical significance, and possible causes.