Abstract

Infections caused by fungi of the order Mucorales have been reported in a variety of marine mammal species. These infections are rare but have been documented in captive animals and occasional isolated infections in the wild.^1,2,3,4,5 In the Pacific Northwest, which includes Washington and Oregon, USA, and British Columbia, Canada, fatal fungal infections in marine mammals have been infrequent, but when detected have been largely caused by Cryptococcus gattii.^6,7,8 In 2012, the first case of mucormycosis in the region was documented in a dead stranded harbor porpoise (Phocoena phocoena) in Washington state. Since then, mucormycosis has been confirmed as the cause of mortality in six other harbor porpoises, one southern resident killer whale (SRKW) (Orcinus orca), one harbor seal (Phoca vitulina), and suspected in two additional harbor porpoises. It was also detected in two other harbor seals with nasal involvement only. The majority of cases occurred within the inland waters of Washington (all harbor porpoises) and British Columbia (two harbor seals); the SRKW was found on the outer coast of Vancouver Island and one harbor seal was stranded in northern Oregon. All cetaceans were found dead on the beach and the three harbor seals initially live stranded and subsequently died. The fungi have been detected histologically in several tissues including brain, lung, spleen, pancreas, kidney, lymph nodes, and skin. The exact fungal species involved are still under investigation; however, PCR screening of affected tissues has identified Rhizomucor pusillus in three harbor porpoises and Lichtheimia corymbifera in one other. In humans, mucormycosis mainly affects immunocompromised individuals.^9,10 Underlying conditions were found in several affected animals such as recent pregnancy/loss of fetus, emaciation, protozoal infection, and herpesvirus, suggesting mucormycosis may also target immunocompromised marine mammals. Reasons for the recent appearance of these fungal infections in marine mammals are unknown-possibilities include soil disturbance due to urban development and/or weather (heavy rains and flooding), an increase in immune suppressed animals, or a change in water quality that would allow these fungi to thrive. The emergence of this disease as a source of marine mammal mortality in Pacific Northwest is of particular concern for the endangered SRKWs that spend part of their lives in this region. Current SRKW population-level stressors potentially include insufficient prey, high levels of contaminants, and noise pollution, which could predispose them to mucormycetes infections.

Acknowledgements

The authors would like to thank Erin Keene of Cascadia Research, Susan Berta and Sandy Dubpernell of the Central Puget Sound Marine Mammal Stranding Network, and volunteers of the Northwest Marine Mammal Stranding Network for their assistance with carcass collection. We also thank Shaun Christean of Middlebury College for her PCR work with Northwest Fisheries Science Center. Funding for this project provided by the John H. Prescott Marine Mammal Rescue Assistance Grant Program and NOAA Fisheries.

* Presenting author

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