An Overview of Marine Mammal Diagnoses in the Pacific Northwest from 1999 to 2004
Stephen A. Raverty1; Joseph K. Gaydos2; Klaus Nielsen3; Ole Nielsen4; Peter S. Ross5; Dyanna M. Lambourn6; Steven J. Jeffries6
Over the last six years, there has been an ongoing effort to recover and conduct post mortem examinations of stranded marine mammals in the coastal region of the northeastern Pacific Ocean (British Columbia and Washington State). Although likely biased compared to wild populations, this information, coupled with targeted serologic surveys of sentinel animals, provides valuable insights into emerging disease concerns of these stocks. To date, a total of 515 individuals have been necropsied, including 30 carnivora, 317 pinnipeds and 168 cetaceans. In addition, 150 wild and rehabilitated harbor seals (Phoca vitulina) and sea otters (Enhydras lutris) were assessed serologically for antibodies to Brucella spp, canine distemper and Leptospira pomona. In British Columbia, anecdotal observations suggest that the most common cause of death of sea otters is physical trauma, incurred by propellers, or more rarely, gunshot. A small number of animals have presented with fibrosing cardiomyopathy. To date, there is no pathologic, serologic or molecular (polymerase chain reaction) indication of Toxoplasma gondii, Neospora caninum or Sarcocystis neurona in sampled animals. Pinniped submissions consist predominantly of neonatal and juvenile rehabilitation animals, frequently with generalized debilitation or immunosuppression associated with suboptimal body condition and secondary opportunistic bacterial or viral (herpesvirus or parapoxvirus) infections. Based on review of historical case records, emerging bacterial pathogens in pinnipeds include Salmonella spp, Brucella spp, Clostridium difficile and multiple antibiotic resistant Escherichia coli. More commonly established bacteria include Pseudomonas spp, E coli, Enterococcus spp, and Aeromonas spp. In addition to these studies, we and colleagues have been conducting studies of environmental contaminants in harbor seals, many of which are immunotoxic and may serve as co-factors in the emergence of some of these pathogens. California sea lion (Zalophus californianus) leptospirosis has a cyclic 3-4 year periodicity in California with sporadic incursions (coinciding with more severe epizootics) into more northern regions approximately every 10-12 years. In 2004, between May and September, there was a significant increase in the number of cases of leptospirosis diagnosed in California (F Gulland, per comm), with stranded, predominantly subadult male sea lions detected in Oregon, Washington and British Columbia from September through December, coincident with the northward migration of these animals. Based on heightened, yet limited surveillance in Washington State and British Columbia, there was clinical and serologic evidence of horizontal dissemination to indigenous otariid stocks. Most cetacean case submissions have been Dall's (Phocoenoides dalli) and harbor porpoises (Phocoena phocoena) with fewer Pacific white sided dolphins (Lagenorhynchus obliquidens), common dolphins (Delphinus delphis), Baird's beaked whales (Berardius bairdii), Fin (Balaenoptera physalus) and killer whales (Orcinus orca). With necropsied cetaceans, localized bacterial infections or generalized septicemia are prime contributors to morbidity and mortality. Bacterial isolates have included Pseudomonas spp, Edwardsiella tarda and multiple Vibrio spp with occasional Salmonella spp and Erysipelothrix rhusiopathiae. For small cetaceans, pooled lung, lymph node, mediastinal lymph node and brain are routinely screened by polymerase chain reaction with universal Brucella spp. and morbillivirus primers, then inoculated on Vero cell lines for attempted virus isolation. In addition, post mortem heart blood is recovered and screened by competitive ELISA and fluorescent polarization assay. Fifty-percent of common dolphins (D delphis) (1/2), 100% of northern right whale dolphins (1/1) (Lissodelphis borealis) 33% of Dall's porpoises (2/6) 40% of harbor porpoises (9/23), 100% grey whales (Eschrichtius robustus)(1/1) and 80% of killer whales (4/5) samples had detectable circulating anti-Brucella antibodies. With the most recent killer whale stranding, Brucella spp was isolated from reproductive tissues, and further efforts to characterize this isolate are underway. Over the course of the last three decades, 17 vessel strikes were documented along the coast of British Columbia and Washington State with five animals reported over a seven-month time span in 2003. The results of this surveillance effort provide an invaluable overview of ecosystem health in the region, and the potential anthropogenic impacts on these stocks.