Serologic Response to Vaccination with Recombinant Canine Distemper Vaccine in Steller Sea Lions (Eumetopias jubatus) over an 8-Year Period
Morbilliviruses are important pathogens of terrestrial carnivores worldwide.1 Commencing in the 1980s, both phocine distemper virus (PDV) and canine distemper virus (CDV) emerged as the cause of mass mortality events in pinnipeds.2 Steller sea lions are a near-threatened species according to the IUCN, with the western subpopulation being listed as endangered.3 While there have been no reports of morbillivirus outbreaks in Steller sea lions, PDV infection was demonstrated in Northern sea otters by molecular genetics and serum neutralization testing.4 Additionally, CDV seroprevalence was noted in wild populations of raccoon dogs, weasels, raccoons, Japanese marten, Siberian weasel, red fox, wild boars and Sika deer in Japan.5 Steller sea lions, Pacific walruses and Northern sea otters inhabiting the northern Pacific Ocean may be at risk for infection since no herd immunity exists in these species.4 In 2008, four healthy female Steller sea lions (Eumetopias jubatus) at the Vancouver Aquarium were vaccinated twice, 3 weeks apart, with a recombinant canarypox vector canine distemper virus vaccine.6 Using the Vero.DogSLAMtag cell line expressing the universal virus receptor for CDV, plaque neutralization testing was performed on serum collected over an initial one year period against CDV and PDV.7 Positive and presumably protective plaque neutralization titers were detected to CDV in all animals 1 month after vaccination (CDV 16, 8, 128, 32), detected in two animals to both viruses one year later (CDV 64 and 16, PDV 8 and 8), with the other two animals having positive titers to CDV (CDV 64 and 16, PDV <8 for both). Serum neutralization testing for CDV performed at Cornell University was considered protective for all four sea lions (128, 96, 96, 64), even 8 years after vaccination. These findings suggest that vaccination of rehabilitated sea lions may be a useful strategy to limit the spread of CDV to susceptible marine species.
The authors wish to thank the Vancouver Aquarium’s Nigel Waller, Malgosia Kaczmarska, Brianna Cairns, Sion Cahoon, Gabrielle Beer, and Amanda Gawor for their assistance with vaccination, monitoring, blood collection and sample handling. We also acknowledge the support of the Department of Fisheries and Oceans Canada for conducting the plaque neutralization testing.
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