Abstract
Leopard seals (Hydrurga leptonyx) are widely distributed and primarily inhabit the Antarctic pack ice and sub-Antarctic islands, ranging between 50-80°S.4 Vagrant leopard seals occasionally haul out in regions of the world remote from Antarctica. These animals are frequently debilitated. On August 5th 1999, a juvenile (estimated age of 8 months), female leopard seal was found hauled out at Garie Beach (151.06839E 34.17015S) in Royal National Park, New South Wales, Australia. The animal was weak and emaciated with skin wounds consistent with cookie cutter shark (Isistius brasiliensis) bites. She was taken to Taronga Zoo, Sydney for assessment and care. The animal was deemed unsuitable for rehabilitation and release and held in permanent care at Taronga Zoo.
In 2008 the leopard seal presented with a 6 month history of intermittent inappetence, lethargy and depression. Various treatments were administered including non-steroidal anti-inflammatories, H2 blockers, and antibiotics. The seal would make dramatic improvements only to become inappetant again with no apparent instigating factor. Further diagnostics were impeded because of the risk of physical restraint and anaesthesia when dealing with this species. Despite medical management and continued supportive care, the animal continued to deteriorate and died in May 2008.
On post mortem examination, there was a pyogranulomatous and necrotizing, multifocal to coalescing, subacute and severe pneumonia with pulmonary congestion, edema and focal fibrosis surrounding a firm mass. Other notable gross findings included serosanguineous and fibrinous hydrothorax, serous hydropericardium, renal papillary necrosis and small nodules in the cortex of the kidneys. Histologically, gram-positive long, branching, filamentous bacteria were present throughout the neutrophilic foci of the lung and granulation tissue surrounding a necrotic portion of the lung, corresponding to the firm mass noted grossly. These filamentous bacteria were partially acid fast on a modified Ziehl Neelsen stain but not on a Kinyoun stain. Nocardia otitidiscavarium were isolated on bacterial culture from the kidney, lung and pleural fluid demonstrating a septicemia. The infection had disseminated to multiple tissues including liver, kidney and brain, manifesting as pyogranulomatous foci.
Nocardia are soil saphrophytes with a worldwide distribution which degrade organic matter and are found in soil, water and on plants.3,4,6,7 Nocardia are gram-positive, partially acid fast, rods that are branched and filamentous in tissue and culture. Nocardia can gain access to its host following contamination of wounds and inhalation.
Nocardia spp. have been reported to cause pyogranulomatous lesions in free-ranging and captive cetaceans and pinnipeds.1,2,8,9 There have been two reported cases of pulmonary lesions in leopard seals,1,8 both of which were males found in Hawke's Bay on the south east coast of the North Island of New Zealand.
Potential sources of Nocardia in this case are aerosolization of the organism from soil due to construction taking place near the enclosure or the presence of an underlying Nocardia infection when the animal was initially taken into care. Nocardiosis should be considered as a differential for pulmonary disease in leopard seals and other pinnipeds.
Acknowledgements
The authors thank Dr Kimberly Vinette Herrin, Dr Frances Hulst, Kaye Humphreys and the marine mammal keepers at Taronga Zoo for their assistance with the management of this case.
References
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