Abstract

Erysipelothrix rhusiopathiae, a gram-positive bacterium, is the causative agent of erysipelas in various animals, including cetaceans. The disease is of concern in marine mammal facilities because it can cause peracute septicemia. Since a vaccine for specific use in cetaceans is not available, a commercial bacterin for use in pigs (ER Bac Plus®, Pfizer, Inc., Exton, PA 19341) has been evaluated and subsequently utilized in cetaceans.^3,5 The purpose of this survey was to evaluate the efficacy of the 10 year long annual vaccination program by determining the IgG antibody levels in several cetaceans over time. For this purpose, a previously described E. rhusiopathiae-specific fluorescent microbead-based assay for pigs¹ based on a recombinant SpaA415 antigen² was modified for cetaceans by using a monoclonal detection antibody specific for odontocetes⁴. Following natural E. rhusiopathiae infections, a 76 to 147-fold increase in antibody levels was detected in a bottlenose dolphin (Tursiops truncatus), a white-sided dolphin (Lagenorhynchus obliquidens) and a killer whale (Orcinus orca). In 10 vaccinated T. truncatus, a mean 35-fold increase in antibody levels was detected two weeks after the booster vaccination, thereby not only confirming the presence of a robust antibody response to the vaccine,³ but also a degree of cross-reactivity between the vaccine antigen and wild-type dolphin strains. Mean antibody levels of the vaccinated T. truncatus were within the same order of magnitude of the peak levels measured following natural infection, and remained approximately 2 orders of magnitude above those of unvaccinated animals. A positive correlation was measured between antibody levels of T. truncatus and number of annual vaccinations. However, the positive effect of additional vaccinations decreased after six annual vaccinations. A negative correlation was detected in T. truncatus which received six or more annual vaccinations between antibody level and length of time since last vaccination, but the rate of antibody decline in these animals suggested that perhaps a longer vaccination interval could be employed. In addition to detecting antibody responses after vaccination or natural exposure, the assay also allowed for the detection of naïve, high risk individuals in other, unvaccinated cetacean species included in the collection.

Acknowledgements

The authors would like to thank the veterinary and animal care staff at SeaWorld San Diego and the Shedd Aquarium for their help with sample collection.

* Presenting author

Literature Cited

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