The clinical significance of Erysiplothrix rhusiopathiae in a collection of cetaceans has varied from dermatologic lesions to an acute septicemic form, both a challenge for even the most experienced clinician. The dermatologic form may vary from the rhomboid-like shaped lesions seen in other species, to less discreet skin lesions. Clinical pathologic findings may be nonspecific but treatment with antibiotics can be successful. The acute septicemic form often results in death with a rapid onset of signs. Initially this may include inappetence and severe leucopoenia shifting to a leuckocytosis progressing to clinical pathologic evidence of organ failure. This clinical course is difficult to stop even with rapid intervention with "appropriate" antibiotics and supportive therapy.
In 2002, three young Tursiops truncatus were infected with the acute form of Erysiplothrix rhusiopathiae over a two month period. The most common initial symptom was loss of appetite. Two of the individuals succumbed within two days of signs while the third responded to a protracted level of intensive care. For the clinician these are not acceptable odds so the effort then turned to prevention measures to increase the odds in favor of the susceptible animals. Since the acute form was not previously identified in the collection, a review of current fish handling practices, individual health variables and potential preventive solutions was conducted by the park veterinarians throughout the Sea World system. A five tiered plan was developed which included: 1) source investigation, improved surveillance, diagnosis, and rapid response in young animals with loss of appetite, 2) research into improved preventive measures with food fish, 3) development of a vaccination plan, 4) serologic research into the vaccination response and titer evaluation for vaccine plan adaptation and 5) investigation into the possible effect on the cellular portion of the immune system after vaccination. Eventually two researchers were involved to pursue the post vaccination titer issues.
Bacterial evaluation from the necropsy of the first affected showed Actinomyces as a predominant organism in the tissues. Further investigation revealed that the organism was a gram-positive rod that was not acid fast positive and was positive for H2S. Follow up bacterial examination of food fish species showed positive cultures of Erysiplothrix rhusiopathiae from capelin, but negative cultures from herring. These cultures were taken initially from the frozen fish blocks (with ice still present) and also from thawed fish iced in buckets. Thawing techniques had been changed previously from an extended wet thaw of fish in fresh city water, to a refrigerated air thaw. The effects of this change on the activity of the bacteria were difficult to evaluate. The wet thaw approach exposed the exterior of the fish to water that was relatively warmer and had chlorine present, since it was a city water source. Stand pipes were also used in the thaw sinks providing a constant water pool. The water flow potentially created a physical removal of exterior material on the fish. Investigation into the previous presence of chlorine and other potential oxidants was begun by one of the authors. Chlorine was added to the thaw sinks at five parts per million followed by a fresh water rinse. Otters would not eat the fish at this level of chlorine so its use was discontinued for their food items. Follow up research showed that this level would need to be much higher to affect the organism but the desired levels would make the fish unpalatable. A fresh water thaw of one hour was also reinstituted in an attempt to decrease the external bacterial load of the fish.
It was noted that the three dolphins involved were all male and less than eight years of age. This appeared to indicate some potential involvement of a developing or compromised immune system, and set the stage for which age class to initially approach with a vaccination strategy. Previous attempts of the use of commercially available whole cell bacterins in the United States were met with a range of negative side effects. These included local reactions at the site of injection to anaphylaxis, in particular at the time of booster administration. With the rate of reaction often reaching the same level as the rate of infection many facilities opted not to continue to vaccinate. Newer vaccines have been developed which include a purified protective protein antigen, 64-kDa, of Erysiplothrix rhusiopathiae. In the United States ER BAC® PLUS bacterin appeared to potentially reduce or eliminate the adverse side effects of the older vaccines. A similar approach in Europe has resulted in no cases of anaphylaxis or infection where the vaccine is used.
As a result of previous vaccine problems, the vaccination program was first begun in four adult male dolphins. Initially only one animal was vaccinated at a time. The dolphins were pulled from the water and placed on foam during the procedure. Two mls of ER BAC PLUS® were given intramuscularly 7.6 cm craniolateral to the dorsal fin with 20 gauge 8.9 cm spinal needles, and the animal's respiratory rate, attitude, and movements were observed for a minimum of 30 minutes. The vaccine was always given on the same side in the group. At the time of vaccination, oxygen, endotracheal tubes, steroids, and epinephrine were present for treatment of potential side effects including anaphylaxis. There were no side effects observed. These animals were then boostered three weeks later with no ill effects. Two months later all dolphins less than eight years of age were vaccinated under the same controlled circumstances in three different groups based on their physical location. The rest of the adults were then vaccinated at the three locations, again with no ill effects. All dolphins were given an initial vaccine, three week boosters, and then revaccinated at six month intervals. In 2004 the post vaccination observation period was decreased to 20 minutes and the animals were returned to the water in areas that could be easily accessed for rapid recovery. At this time the vaccination of six month old calves was begun. Pregnant females have also been vaccinated without ill side effects. Side effects from the two year program have been minimal relative to prior vaccine use. Only one individual showed possible bouts of retching but this could not be blamed solely on the vaccine and no treatment was required.
Serum was taken from each individual prior to injections in the hope that titers would verify the effectiveness of the vaccine. Initial findings of the serology program are included in this session. Post vaccination blood work has shown some increase in fibrinogen levels though the direct relationship to the vaccine has yet to be fully established. At the present time the vaccination program is based on six month boosters though the authors hope that further investigation may lead toward the potential development of a more specific DNA vaccine that would eliminate the use of the current vaccine and its carrier compounds. Additional research would include clarifying the duration of protection from vaccination which may not determined by classic titer level evaluation.
The authors would like to thank the laboratory staffs at the Sea World parks, the laboratory staff at Dr. Patterson's laboratory and the animal care staffs and veterinary technicians for their help in researching the issues and instituting the vaccination programs.
ER BAC®PLUS Pfizer Inc., Pfizer Animal Health, 235 East 42nd Street, New York, NY 10017