Abstract

West Nile virus (WNV) first appeared in the United States in 1999 when encephalitis and death in birds, horses and humans were linked to transmission by mosquito vectors.¹ The virus has now been identified in all 48 contiguous states and Canada and has caused death in numerous species including marine mammals such as harbor seal (Phoca vitulina)and northern sea otter (Enhydra lutris).^2,3 Although WNV has not been detected in Alaska, there is risk of introduction via migratory birds, as well as the possibility of importing infected mosquitoes or animals via airline flights.

Beginning in 2004, marine mammals housed at the Alaska SeaLife Center, including 7 adult Steller sea lions (Eumetopias jubatus), were vaccinated against WNV using a live, recombinant canarypox vector vaccine,^a administered according to label recommendations for horses. Two 1-ml doses were injected intramuscularly 4 to 6 weeks apart with boosters given annually. Serum samples from all exams are routinely archived at -80°C. A subset, including samples from before and after vaccination, was submitted to a diagnostic laboratory^b for determination of antibody response to vaccination using a standard WNV plaque reduction neutralization assay (SN). Animals were monitored following each vaccination and no adverse reactions were noted. SN titers were negative prior to vaccination and rose after the initial two doses to levels considered protective in horses.⁴ Titers decreased during each year in most animals but increased after booster doses and always remained at 1:10 or greater.

Vaccination against WNV with a commercially available recombinant canarypox virus vaccineappears to be safe and can induce presumptively protective levels of circulating antibody in healthy adult Steller sea lions.

Endnotes

a. Recombitek, Merial Inc., Athens, GA, 30601, USA
b. Cornell University, Animal Health Diagnostic Center, Ithaca, NY 14853 USA

Acknowledgements

The authors thank the Alaska SeaLife Center Husbandry staff for their observations and excellent care of the animals reported here and the ASLC Pinniped Research Program for their financial support. The Steller sea lions at the ASLC are held under NOAA Permit 14334.

* Presenting author

Literature Cited

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