2004 LEPTOSPIROSIS OUTBREAK AMONGST CALIFORNIAN SEA LIONS

Authors: CULLEN, PAUL - UNIV. OF WASHINGTON; GULLAND, F - MARINE MAMMAL CENTER; Zuerner, Richard; RAVERTY, S - BC MINISTRY OF AGRICUL; LAMBOURN, D - WASH. DEPT. FISH AND WILD; CAMERON, C - UNIV. OF WASHINGTON

Submitted to: International Leptospirosis Society Meeting Abstracts and Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/2005
Publication Date: 11/13/2005
Citation: Cullen, P.A., Gulland, F., Zuerner, R.L., Raverty, S., Lambourn, D., Cameron, C.E. 2005. 2004 Leptospirosis outbreak amongst Californian sea lions [abstract]. International Leptospirosis Society Meeting Abstracts and Proceedings. p. 328.

Interpretive Summary:

Technical Abstract: Background: Leptospirosis outbreaks among marine mammals, and specifically California sea lions (Zalophus californianus), have resulted in large scale, cyclic epizootics since the early 1970s, with a distinct 3-4 year periodicity. During 2004 over 300 sea lions died along the central California coast, and mortalities were tracked off the coasts of Oregon, Washington and British Columbia. Preliminary investigations indicate renal failure as the proximate cause of death for these animals, and our hypothesis is that this renal failure resulted from infection with Leptospira. Methods: To determine the cause of death of California sea lions and other assorted marine mammals stranded off the west coast of North America in 2004, several diagnostic modalities were used. These included clinical observations of live stranded animals (presumptive diagnosis by pattern recognition), clinical chemistry with evidence of impaired renal function, elevated or rising paired titers (serology) and comprehensive post mortem examination of dead, beach cast or euthanized animals, including histopathology using immunohistochemistry. In addition, polymerase chain reaction (PCR) assays were performed on a selection of DNA samples extracted from clinical specimens including urine, renal tissue, feces and urine-contaminated sand samples collected from the vicinity of the stranded animal. Results: A total of 478 California seal lions were examined, of which 303 (63.4%) were determined to have leptospirosis. L. interrogans serovar Pomona was the most common cause of leptospirosis in California sea lions. Sea lions exhibiting no clinical symptoms that had positive serology and/or PCR were also identified. Samples from 30 out of 34 marine mammals (including California sea lions, elephant seals, Steller’s sea lions and a harbour seal) that were subjected to PCR analysis were PCR positive for Leptospira. The presumptive cause of death in each of these thirty animals was attributed to leptospirosis via clinical and pathological analyses. Using two different primer sets we differentiated between the two species L. interrogans and L. kirschneri. Of the PCR positive samples only the elephant seal was PCR positive for L. kirschneri. Conclusions: The 2004 marine mammal die off along the coast of North America was the result of an outbreak of leptospirosis. As in the previous outbreaks the causative agent was deemed to be L. interrogans serovar Pomona. The amplification of L. kirschneri from an elephant seal, but no other marine mammals, may reflect a host specificity of leptospiral strains for different marine mammal species. The data collected also suggests the presence of asymptomatic carrier animals in marine mammal populations. The PCR methodology employed was deemed to be sensitive and specific in the context of marine mammal leptospirosis. Key words: Leptospira, Leptospirosis, California Sea Lion, PCR