Abstract
Erysipelothrix rhusiopathiae is a zoonotic, gram-positive, facultative anaerobic rod or non-branching filament.1,2 It has been isolated from a wide variety of animals, including marine mammals and the mucous layer of fish.3,4 Disease from E. rhusiopathiae has been reported in both captive and free-ranging cetaceans, and can manifest as cutaneous rhomboidal lesions with mild systemic involvement or fatal septicemia with or without cutaneous lesions.5,6,7,8 Cetaceans are likely exposed to E. rhusiopathiae through ingestion of infected fish, inoculation from the teeth of conspecifics, or opportunistic colonization of wounds.9,10 Current literature on E. rhusiopathiae in free-ranging cetaceans is limited to a few case reports.6,7,10 The number of free-ranging cetaceans affected by E. rhusiopathiae has not been evaluated. The purpose of this study was to determine the prevalence of E. rhusiopathiae and describe the gross and histopathological findings associated with E. rhusiopathiae in stranded cetaceans in England and Wales between 1990 and 2019.
Microbiology records for 1127 cetaceans stranded on English and Welsh beaches and examined by the Cetacean Strandings Investigation Programme at the Institute of Zoology between 1990 and 2019 were retrospectively reviewed. Seven cases were identified in which E. rhusiopathiae was isolated and identified from at least one organ: three bottlenose dolphins (Tursiops truncatus), three harbor porpoises (Phocoena phocoena), and one short-beaked common dolphins (Delphinus delphis). Key organs for E. rhusiopathiae isolation were the kidney (7/7), liver (6/6), and brain (5/5). Overall prevalence was 0.62% (7/1127; 95% CI: 0.30–1.28%). Prevalence was significantly higher in bottlenose dolphins at 21.4% (3/14; 95% CI: 7.6–47.9%) than in harbor porpoises at 0.39% (3/779; 95% CI: 0.13–1.13%) or short-beaked common dolphins at 0.47% (1/212; 95% CI: 0.08–2.62%).
Gross necropsy reports for the seven E. rhusiopathiae cases were reviewed and summarized. A single veterinary pathologist performed histopathology for five of the E. rhusiopathiae cases; histopathology was not performed for two cases because tissues were missing or too autolyzed for meaningful interpretation. Gross findings included pulmonary edema (5/7), petechial and ecchymotic hemorrhage (5/7) and/or vascular congestion (4/7) in various organs, and serosanguineous effusion (3/7: pericardial [3/7], pleural [2/6], and abdominal [2/6]). Rhomboidal dermal lesions were not observed in any case. On histopathology, congestion (5/5), bacterial emboli (4/5), and/or hemorrhage (4/5) was commonly observed in multiple organs; acute renal tubular injury (2/5) and pulmonary edema (2/5) were less commonly observed. Bacterial emboli all consisted of gram-positive filamentous rods.
The gross and histopathological findings in conjunction with the isolation of pure E. rhusiopathiae from multiple organs were consistent with E. rhusiopathiae septicemia. Routine bacterial isolation and identification in conjunction with histopathology were essential in identifying E. rhusiopathiae in these cetaceans since gross lesions were often subtle and nonspecific. Although E. rhusiopathiae septicemia was determined to be the cause of death in all seven cases described here, it was an uncommon cause of mortality in this population overall.
Acknowledgements
The authors would like to thank the Department for Environmental, Food, and Rural Affairs and the Devolved Governments of Scotland and Wales, which co-fund the Cetacean Strandings Investigation Programme. We greatly appreciate the technical advice and expertise provided by Carol Persaud and Carmel Aldridge of MAST Group Ltd. and Helen Wilson of Thermofisher diagnostics, UK.
*Presenting author
+Student presenter
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