Mapping Novel Pathogens and Diseases Impacting Marine Mammal Health

During the past 10 years, systematic and comprehensive necropsies have been conducted in the NE Pacific on over 1,600 stranded harbor seals, Steller sea lions, sea otters, California sea lions, northern fur seals, Guadalupe fur seal, elephant seals and a variety of cetacean species.  Infectious diseases accounted for 30-40% of mortalities of the stranded marine mammals. Comparing the diseases found in marine mammals with terrestrial mammals has identified similar, and in many cases genetically identical disease agents.  Molecular investigations have tracked and documented gene flow and the transfer of pathogens from land to the sea.  Some of the disease agents, such as the marine variant of Coxiella burnetii documented in harbor seals, sea lions, harbor porpoises, and fur seals, appear to be limited to the ocean environment.  However, other infectious agents, such as Cryptococcus gatti detected in porpoises, indicate environment contamination and a risk of exposure and infection to humans and other animals in the region.  Multiple antibiotic resistance has also been documented in Enterococcus spp and Escherichia coli recovered from stranded marine mammals at a much higher rate than bacteria isolated from farm animals in British Columbia’s Fraser Valley.  Genetic fingerprinting further suggests that this increase in antibiotic resistance correlates with an increase in multiple environmental pressures.  Culturing bacteria from the surface microlayer of the ocean has further revealed a variety of bacteria and fungi, which are not only recovered from diseased marine mammals, but also from humans and in some cases other vertebrate and invertebrate species. Combining advanced molecular techniques with standard veterinary diagnostic examinations of marine mammals raises concerns about the potential implications for humans exposed to shared pathogens.  Comprehensive pathologic investigations into the causes of death of beach-caste marine mammals thus provide valuable insights into not only the health of marine mammals, but also into our long-term health and that of our marine ecosystems.