Abstract
Dolphin morbillivirus (DMV) has caused previous outbreaks of disease in bottlenose dolphins (Tursiops truncatus) in the Mid-Atlantic region of the United States east coast (1987–88),1,2 the Gulf of Mexico (1992, 1994),3,4 and in striped dolphins (Stenella coeruleoalba) in the Mediterranean (1990–92, 2007–8).5,6 An unusual mortality event (UME) was declared by the National Marine Fisheries Service on August 8, 2013 due to increased numbers of bottlenose dolphin strandings documented in New York, New Jersey, Delaware, Maryland and Virginia during the months of July and August. Currently the geographic scope of the event extends from New York to the Florida Keys, and the UME is still ongoing.7
From July 1, 2013 to December 31, 2014, > 1500 bottlenose dolphins stranded within the UME area with approximately 18% of animals stranding alive or fresh dead, and 82% of the carcasses in moderate to advanced states of decomposition. Gross necropsy findings included dermal, oral, joint, and pulmonary lesions. Consistent histopathology findings included bronchointerstitial pneumonia and/or pulmonary fibrosis, lymphoid depletion, syncytial cells and viral inclusions. Secondary bacterial, fungal, viral (non-morbillivirus), and protozoal infections were observed. Tissue samples from dolphins were tested for morbillivirus via immunohistochemistry (IHC) and/or polymerase chain reaction (PCR) and positive PCR results were confirmed by sequencing as dolphin morbillivirus.8 From a few live stranded dolphins, serum was tested for morbillivirus neutralizing antibody and DMV was isolated in Vero-SLAM, MDCK-SLAM, and Mv1-Lu-SLAM cells from several dolphins.9 The presence of morbillivirus in the cell cultures was indicated by virus-induced cytopathic effects including cell death and/or the formation of syncytia, and confirmed by electron microscopy and PCR.
Tissue samples from 291 dolphins were tested for morbillivirus via IHC and/or PCR, with 93% being DMV-positive (270 of 291); of these, 88% (237 of 270) had results confirmed by sequencing. Serum from 15 DMV-positive bottlenose dolphins was tested for morbillivirus neutralizing antibody and yielded titers ranging from 32 to 8,192. Virus isolation was successful on 14 animals to date. Preliminary whole genome sequencing of the DMV genome in eight bottlenose dolphins has found the sequences to be > 99.9% similar to each other, and distinct from other DMV isolates. This UME is still ongoing, and all results presented here are preliminary. Currently, the event appears to be primarily caused by a DMV outbreak that is mostly affecting bottlenose dolphins; although a few other cetacean species have also been infected. Additional research evaluating the contribution of co-infections, biotoxin exposure, and contaminants to the UME is pending. Lastly, research is ongoing to better understand the impacts of this large-scale outbreak on bottlenose dolphin populations and affected coastal stocks.
Acknowledgements
The authors wish to acknowledge those people that contributed to the dolphin data and sample collection and sample analyses, including the staff and volunteers of Clearwater Aquarium; Coastal Carolina University; Florida Fish and Wildlife Conservation Commission; Georgia Aquarium Conservation Field Station; Georgia Department of Natural Resources; Harbor Branch Oceanographic Institute; Hubbs-SeaWorld Research Institute; International Fund for Animal Welfare; Marine Animal Rescue Society; Marine Mammal Conservancy; Marine Mammal Stranding Center; Maryland Department of Natural Resources; Mystic Aquarium; Mote Marine Laboratory; National Aquarium; National Ocean Service-Hollings Marine Laboratory; National Park Service; National Veterinary Services Laboratories; New Jersey Department of Agriculture; New Jersey Department of Environmental Protection; North Carolina Department of Environment and Natural Resources; North Carolina State University; North Carolina Division of Marine Fisheries; North Carolina Maritime Museum; MERR Institute; Riverhead Foundation for Research & Preservation; Smithsonian National Museum of Natural History; South Carolina Department of Natural Resources; Virginia Aquarium and Marine Science Center; University of North Carolina at Wilmington; and University of Pennsylvania/New Bolton Center.
* Presenting author
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