1SeaWorld, Orlando, FL, USA; 2SeaWorld, San Diego, CA, USA; 3SeaWorld, San Antonio, TX, USA; 4University of Mississippi, Hattiesburg, MS, USA; 5University of Florida, Gainesville, FL, USA; 6School of Veterinary Medicine, University of California, Davis, CA, USA
Abstract
Erysipelothrix rhusiopathiae, a gram-positive bacterium, causes two forms of disease in cetaceans, a chronic skin condition and a peracute, often fatal septicemia. A thorough review of this disease was compiled on compact disk in 2000 after the First International Workshop on Erysipelas in Cetaceans.1
In 2002, acute Erysipelothrix septicemia was diagnosed in three young male captive-born Tursiops truncatus at SeaWorld Orlando. Subsequently, all SeaWorld parks adopted a more rigorous Erysipelothrix prevention program, which focused on food fish preparation and cetacean vaccination. Frozen fish are thawed for approximately 24 hours in refrigerated temperatures before submergence in running tap water for 60 minutes. Chlorine levels greater than 12 ppm have not been found to kill the E. rhusiopathiae organism in vitro, thus, the benefit of rinsing fish with tap water has been predominately dilutional, not bactericidal. Rinsing of mucus from fish skin helps reduce surface bacterial pathogen load prior to feeding the fish to cetaceans.
The current vaccination program targets all dolphins greater than 6 months of age. Two milliliters of ER Bac® Plus (Pfizer, Inc., Pfizer Animal Health, New York, NY, USA) is administered intramuscularly, boostered 3–4 weeks later and every 6 months thereafter. Originally developed for the porcine industry, the vaccine bacterin is a 64 kDa surface protein found in most variants of E. rhusiopathiae. Dolphins are monitored for signs of adverse reactions during the first 20–30 minutes following vaccination. To date, over 120 dolphins have been vaccinated multiple times without notable adverse side effects, such as local vaccine reactions or anaphylaxis.
Preliminary research of Erysipelothrix titers shows peak detectable titers within 2–4 weeks of vaccination and waning of titers over a 5-month period. The humoral immune response of dolphins to the vaccine antigen is very similar to the response reported in swine. While antibody titers of swine declined by 10 weeks after immunization, 75% of the pigs were protected from a challenge infection 20 weeks after immunization.2 Until more information is available, we recommend an immunization schedule consisting of an initial immunization, a second immunization at 4 weeks, followed by booster immunizations every 6 months.
The dolphin cellular immune response to ER Bac® Plus vaccination is currently under investigation. Evidence of such cellular immune responses will be assessed by measuring E. rhusiopathiae-induced production of cytokine mRNA in cryopreserved mononuclear leukocytes. Development of real-time PCR assays for quantitation of Tursiops IL-2, IL-4, IL-5, IL-6, TNFα, and IFN has been completed and antigen-specific assays have been initiated.
Acknowledgments
The authors would like to thank the SeaWorld animal care, training, and laboratory staffs and veterinary technicians for their assistance with this program, as well as curatorial staff for their support of this program. We would also like to thank the staff in Dr. Patterson’s and Dr. Stott’s research laboratories for their help with this project.
Literature Cited
1. Boehm, J.R., G. Lacave, and R.A. Patterson (eds.). 2000. In: Proc First Int Workshop on Erysipelas in Cetaceans. John G. Shedd Aquarium, Chicago.
2. Shive, B. 1999. ER Bac® Plus: extended duration of immunity for control of erysipelas in swine. Pfizer Animal Health Technical Bulletin. Pfizer, Inc., Exton, PA. 1–6.