Abstract

A mature, intact, aquaraium-housed, female Pacific white-sided dolphin (Lagenohrynchus obliquidens) presented with a one-day history of reduced appetite and reluctance to perform learned behaviors. Physical examination revealed an approximately 1 cm² malodorous necroulcerative lesion along the right margin of the tongue, midway between the base and the apex. Results of a CBC and serum chemistry profile were consistent with subacute to acute marked inflammatory response. Erysipelothrix rhusiopathiae was isolated in pure culture from a blood sample collected aseptically from a fluke vascular plexus at the time of physical examination. The dolphin was treated with an initial intravascular dose of ceftriaxone followed by a course of oral cephalexin t.i.d. for ten days. Clinical response was excellent. The animal's appetite returned to normal the day following ceftriaxone injection. The tongue lesion resolved by day 5 of treatment and a follow up blood culture on day 5 was negative for bacterial growth. The animal remains clinically normal to date.

Morbidity and mortality of cetaceans due to infection with Erysipelothrix rhusiopathiae has been recognized for over fifty years now and other authors have also reported the successful treatment of erysipelothrix infections (Seibold and Neal, 1956; Simpson et al., 1958; Calle et al., 1993) This disease and its importance to aquarium held cetaceans have been broadly investigated during the fifty-plus year period that it has been recognized. Serologic surveys suggest exposure to this organism is widespread among marine mammals both free-ranging and held under human care (Calle et al., 1993). Microbiologic surveys indicate the organism can be readily, although unpredictably, isolated from a variety of fishes and invertebrates commonly fed to marine mammals as well as from biosamples collected from clinically normal animals (Boehm et al., 2001; Greenwell et al., 2002). A number of clinical isolates have been characterized, a number of serologic assays have been developed, and a number of vaccination and prevention strategies have been implemented. Yet, as this case illustrates, the clinical problem persists. Why?

We propose here a hypothesis, the aquatic animal hygiene hypothesis. Reports in the literature of clinical erysipelas infection in marine mammals more often than not describe cases in animals held under human care and apparently involve a disproportionate number of animals housed in closed or semi-closed systems. We suggest that long term housing in aquatic systems that are manipulated to control the microbial ecology of the water leads to an altered functional immune response in resident animals. The hygiene hypothesis as presented in human medicine has been offered to explain the recently observed marked increase in prevalence of immune mediated disorders in individuals reared in hygienic Western conditions (Vercelli, 2006). This hypothesis has not been completely accepted or tested in the human medical literature however; the parallel to our clinical observations with aquatic systems is profoundly intriguing.

We further suggest that aquatic systems with controlled microbial milieus offer a unique animal model and potential test platforms for the investigation of the influence of long-term housing in closed systems on immune modulation and health of residents. An improved understanding of the unique influences of closed system environments on animal health will lead to recommendations for altering current management strategies to further promote optimum animal health. Investigations to test the aquatic animal hygiene hypothesis may also provide information important in the development of closed systems for long-term human habitation such as submarine and space habitats.

References

1.  Boehm JR, G Lacave, RA Patterson. 2001. Proceedings of the First International Workshop on Erysipelas in Cetaceans.

2.  Calle PP, DE Kenny, RA Cook. 1993. Successful Treatment of Suspected Erysipelas Septicemia in a Beluga Whale (Delphinapterus leucas). Zoo Biology 12:483-490.

3.  Greenwell MG, JR Boehm, BM Harris. A One-year Surveillance Program for Erysipelothrix rhusiopathiae: Methodologies, Findings and Recommendations. IAAAM Proceedings 2002.

4.  Seibold HR, JE Neal. 1956. Erysipelothrix Septicemia in the Porpoise. JAVMA 1:537-538.

5.  Simpson CF, FG Wood, F Young. 1958. Cutaneous Lesions on a Porpoise with Erysipelas. JAVMA 1:558-560.

6.  Vercelli D. 2006. Mechanisms of the Hygiene Hypothesis--Molecular and Otherwise. Current Opinion in Immunology. 18:733-737.