A long term captive juvenile female nurse shark (Ginglymstoma cirratum) was presented with an acute onset of depression, inappetence, and rapid respiration. Based on these clinical signs, a bacterial septicemia was suspected and antibiotic therapy was initiated with Gentamicin Sulfate (6.0 mg/kg) intramuscularly. Antemortem, blood samples revealed many gram positive cocci and blood cultures grew a pure Lancefield Group B Streptococcus. The shark died within 24 hours of presentation. Gross necropsy findings showed mud multifocal external petechiation ventrally, and no other pathological lesions internally. Histopathological findings showed a moderate diffuse endocarditis, a multifocal, suppurative nephritis, and a mild oophoritis which were consistent with streptococcosis. The primary etiology for streptococcosis in this shark was presumptively attributed to the practice of feeding the shark sick live and/or dead tropical freshwater fishes. High nitrate levels and undernourishment may have also contributed to the development of disease.

Introduction

Though little is known about bacterial diseases of sharks, pathogenic bacterial infections are not uncommon. In particular, Vibrio carchariae has been isolated from brown sharks (Carcharhinus plumbeus) showing clinical signs of meningitis (Grimes, et. al., 1984). Generally shark internal tissues are sterile; but, muscle, kidney, liver, and spleen from asymptomatic sharks can contain from 100 to 10,000 bacteria per gram of tissue (Grimes, et. al., 1985). It is speculated that during periods of a compromised immune system a rapid systemic invasion by resident bacteria occurs. In addition, this rapid systemic invasion of bacteria (especially ureolytic bacteria) may cause further compromise by alkalinization of the blood through excessive urea hydrolysis (Grimes, et. al., 1984). In this case report, a Lancefield Group B Streptococcus septicemia was diagnosed in along term captive female nurse shark (Ginglymostoma cirratum). Though streptococcosis has not been noted in sharks in the literature, it has been noted in teleosts (Robinson, 1966, Taniguchi, 1983, Taniguchi, 1982b, Kusuda and Kimura, 1978). In particular, oral transmission through the food has been considered a primary means of disease transmission in yellowtails (Seriola spp.) (Kusuda and Kimura, 1978). For this reason, a similar etiology was suspected in this case based on the history, clinical signs, and necropsy findings. High nitrate levels and undernourishment may have also contributed to the development of disease in this case.

Case History

On November 25, 1991, a juvenile female nurse shark (Ginglymostoma cirratum) was examined by zoological medicine clinical staff and students of the North Carolina State University College of Veterinary Medicine. This shark had been in captivity for at least the past 11/2 years, housed separately in a 100 gallon display tank at a local pet store. Five months previously this shark was examined as a routine health check and was noted to be undernourished. The shark's diet at that time consisted only of sick and/or dead freshwater tropical fishes from the same pet store. The owners were counseled to stop this practice and given suggestions for providing a better plane of nutrition.

The shark was presented the second time with a one week history of depression, inappetence, and general disinterest in her environment. Toward the end of that week her condition had rapidly deteriorated. On physical examination the shark appeared depressed with a rapid respiration rate of approximately 60 bpm. The shark was still thin, but had gained weight and improved in condition over the preceding five months. The practice of feeding sick or dead tropical fish and goldfish had not been discontinued.

Water quality parameters were considered in taking the history and the lack of water changes led us to believe high nitrate levels might be contributing to the respiratory distress. The owners had been routinely testing the water for nitrates using a colorimetric test kit (Tetra Test Kit, Tetra), but the readings were consistently nominal. After discussion of the history we decided to test the nitrate levels with another form of test kit (Master Test Kit, Aquarium Pharmaceuticals). This test revealed nitrate levels greater than the scale of the colorimetric comparator for the kit (140 ppm).

In addition to water quality issues, the general malaise of the animal, a barely perceptible ventral hyperemia, and the rapid respiration suggested the possibility of bacterial septicemia. The decision was made to transfer the shark to a clean tank because of the very poor condition of the water in the original tank, and the unavailability of prepared water for less drastic water changes. During the transfer the shark showed poor muscle tone and was essentially non-reactive. A blood sample was drawn from the caudal vein and 6.0 mg/kg Gentamicin Sulfate intramuscularly was administered empirically, for an estimated body weight of 1.0 kg. The blood sample revealed many gram positive cocci on examination of stained smears. These subsequently were grown as a pure culture of a Lancefield Group B Streptococcus. The biochemical profile and antibiotic sensitivities with Kirby-Bauer methodology are shown in tables 1 and 2, respectively. The susceptibility pattern showed resistance to Gentamicin, but susceptibility to Erythromycin and several other antibiotics (see table 2). Before a change in antibiotic regimen could be initiated, the shark died within 24 hours of presentation.

The actual weight of the shark at postmortem examination was 0.6 kg. It was in fair nutritional condition with small adipose stores evident within the abdominal cavity. The significant gross necropsy findings were limited to diffuse petechiation on the ventral surface from the rostrum to the mid-thoracic region, with the ventral portions of the pectoral fins most severely affected.

Histopathological examination revealed a diffuse, moderate endocarditis with a heterophilic and lymphocytic infiltrate together with large numbers of gram positive cocci. An interstitial nephritis and an oophoritis consisting of heterophilic, lymphocytic, and plasmacytic infiltrates and numerous Gram positive cocci, were also present In addition, bacterial colonies were present throughout the myocardium, liver, and spleen. The lack of the concomitant inflammatory response was suggestive of a peracute septicemia; however, postmortem bacterial proliferation can not be ruled out in light of the indeterminate postmortem interval (less than 12 hours), as the shark was found dead and was refrigerated before the postmortem was performed.

Discussion

In this shark the clinical signs and pathological lesions were consistent with a bacterial septicemia, but not diagnostic of streptococcicosis. In yellowtails (Seriola spp.) common clinical signs have included petechial hemorrhages, exophthalmia, and abdominal distension (Austin and Austin, 1987). These signs were not observed in this case. Other diseases in sharks share these clinical signs including vibriosis (Stoskopf, 1992 in press). The acuteness of the final stage of the disease in this case was similar to that noted previously in yellowtails with streptococcal septicemia. In yellowtail streptococcicosis the lag time between the spread of the bacterial pathogen to various organs and the development of clinical signs has been one to three days (Taniguchi, 1983).

Based on the dietary history of this shark we presumptively speculate that the ingestion of contaminated food was the primary etiology of disease. In teleost fishes contaminated diets have served as an important source of infection (Austin and Austin, 1983). In particular, in oral inoculation experiments in yellowtails (Seriola spp.) there was a very high mortality when streptococci were applied under the skin of the food fish compared to on the surface of the food fish (Taniguchi, 1982b). Food preparation may also affect the incidence of infection, since the artificial peroral infection prevalence of yellowtails was higher when chopped inoculated food was fed compared to whole food (Taniguchi, 1982a).

The pathogenesis of peroral streptococcicosis is not completely known currently, although the intestine appears to be a preferred site of colonization in teleosts (Kusuda and Kimura, 1978). The histopathological lesions noted in the kidney of the shark were consistent with similar bacterial septicemia in fish. In teleosts the kidneys are speculated to have a role in the elimination of bacteria from the bloodstream (Hatai, 1972).

Environmental conditions may have contributed to the pathogenicity of a streptococcal infection in this shark. Experimentally, fish reared under good environmental conditions and given high quality food tend to be more resistant to developing disease when inoculated with bacteria (Taniguchi, 1983). The elevated nitrate levels in the shark's tank and poor diet probably contributed to the development of clinical illness.

This shark was treated with Gentamicin Sulfate, but subsequent Kirby-Bauer bacterial sensitivity results showed resistance to this antibiotic. The current treatment of choice for streptococcal septicemia in yellowtails is erythromycin dosed at 25 mg/kg for 4 to 7 days (Kitao, 1982). Ibis treatment has worked better than either oxytetracycline or ampicillin (Shiomitsu et. al., 1980). For this reason, the use of macrolide antibiotics may be more effective than the aminoglycosides in similar cases.

In conclusion, the etiology of streptococcosis in this nurse shark (Ginglymostom cirratum) was presumptively attributed to the practice of feeding the shark diseased sick and/or dead freshwater tropical fishes. The problems of high tank nitrate levels and poor body condition probably exacerbated if not elicited the clinical signs of streptococcal septicemia. The clinical course of streptococcosis in this shark was similar to previously documented streptococcosis in yellowtails. Speculatively, this case illustrates the potential adverse effects of feeding a contaminated diet to sharks. The etiology of bacterial infection and associated pathogenesis in sharks remains a clinically important area for future studies.

Table 1. Bacterial Isolate Biochemical Profile

Table 2. Kirby-Bauer Qualitative Antibiotic Susceptibility Results

Acknowledgements

The authors thank Carol Lemon, College of Veterinary Medicine, N.C. State University who performed the bacteriological studies on this case and Janet Barnett, College of Veterinary Medicine, N.C. State University for typing the manuscript.

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