Abstract

At least six mucormycotic cases involving both captive and wild marine mammals have been reported. The two organisms identified in these cases were either Saksenaea vasiformis or Apophysomyces elegans.³ Both of these fungi are extremely rare and the number of cases reported in marine mammals may indicate a disproportionate susceptibility to these organisms. Human infections with these agents, despite aggressive therapy to include radical resection of infected limb or tissue, is associated with greater that 80% mortality.¹ In dolphins, treatment for these organisms has never shown any promise and all cases have resulted in death. On 16 January 2000, we were presented with a 20-mo-old bottlenose dolphin, in apparent good health, that had a 5-cm by 2-mm laceration on the dorsal midline immediately caudal to the dorsal fin. By 20 January 2000, the laceration had grown to 10 cm in diameter and was slightly elevated. Two additional 4-cm diameter purplish colored lesions were observed. A blood sample revealed an elevated total white blood cell (tWBC) of 22,500 cells/mm³ characterized as a regenerative left shift (Table 1). The lesion on the lateral side was biopsied and the animal was started on the antifungal, itraconazole (Sporanox®, Janssen Pharmaceutica Inc., Titusville, NJ 08560 USA) and antibiotics.

Cultures and histopathology confirmed that the infectious agent was from the family mucorales. On 25 January 2000, the lesions had doubled in size. Serum chemistries reflected the progressive nature of the fungus with elevations in CK (creatinine kinase, 3248 U/L) and LD (lactate dehydrogenase, 1154 U/L) (Table 2). The animal was placed on the experimental anti-fungal, Nyotran® (Donated by Aronex Pharmaceuticals, Inc., The Woodlands, TX 78381 USA). Nyotran® is a liposomal form of nystatin and must be administered i.v. with a slow infusion rate. The liposomal formulation is believed to reduce nephrotoxicity. The drug was initially dosed at 4.2 mg/kg for a total dose of 700 mg, s.i.d. The drug was reconstituted using 5% dextrose in water (D5W ) and administered i.v. in the dorsal inter-vertebral venous sinus, approximately one-half the distance from the fluke to the caudal edge of the dorsal fin over a 2-hr period. A common drug related reaction observed in humans is pyrexia, which was also observed in this dolphin. Twenty-four hours after the first dose, the dolphin's BUN (blood urea nitrogen) and creatinine had elevated to 88 mg/dl and 5.1 mg/dl, respectively. The animal was immediately placed on 3 L of calf milk replacement formula² p.o. q 8 hr and 2 L of LRS (Lactated Ringers solution) p.o. q 8 hr. In addition, the animal was administered 1 L of D5W i.v. prior to each additional dose of Nyotran®. Finally, the Nyotran® dose was cut to 400 mg i.v. s.i.d. Treatment continued at this level for 5 days until BUN and creatinine were normal (Table 2). Starting 31 January 2000, the Nyotran® dose was increased by 50 mg every other day (e.o.d.) until it reached 550 mg s.i.d. on 7 February 2000. Serum chemistries returned to near normal levels by 17 February 2000 (Table 2). Total WBC, which peaked at 65,900 cells/mm³ on 1 February return to 12,0000 cells/mm³ by 17 February. Due to an apparent response to treatment, and the animal's increasing discomfort during drug administration, the treatment schedule was changed to e.o.d. on 7 February and discontinued on 14 February. The lesion on the dorsal peduncle, caudal to the dorsal fin, sloughed on 18 February, leaving a 10 x 10 x 5 cm cavity. Ten days after discontinuing the Nyotran®, the margins of each lesion became active. Additional biopsies of wound margins cultured fungi. The cranial lesions on the side of the animal sloughed to the depths of the ribs, while the caudal lateral lesion had undermined the dorsal fin. Due to the extent of lesional progression and the animal's deteriorating condition, the dolphin was euthanatized.

Necropsy revealed three open lesions up to 20 cm in diameter with depths as deep as 12 cm. Also, enlarged and edematous adrenal glands and small pyogranulamatous masses throughout the lungs were observed. Apophysomyces elegans was cultured from all of these sites and histopathology confirmed the presence of fungal hyphae. All fungi in the class zygomycete are aggressive organisms that invade the vascular system causing extensive infarction and tissue necrosis. In dolphins, all of the previous cases have resulted in progressive advancement of the infection until death or euthanasia. Although this case had a similar outcome, apparent remission of the disease was observed during the treatment course. This is typical for human mucormycotic cases that exhibit "remission" of the infection during treatment. In these cases, the continual clinical dilemma is how long to treat an animal after resolution is believed to have been reached. This must be balanced with how well the animal is tolerating the treatments. In this case, and despite sedation, the animal was at a point where she would not tolerate the i.v. administration. Despite the outcome, we feel that if while pending the initial biopsy results we had acted immediately by placing the animal on Nyotran® and by performing radical resection of the skin and muscle lesion (excisional biopsy) while they were relatively small, the animal may have had a slim chance of survival.

Table 1. Hematologic parameters from bottlenose dolphin with an A. elegans infection.

a. Reference value from animal prior to infection.

Table 2. Serum chemistry values from a bottlenose dolphin with an A. elegans infection.

a. Reference value from animal prior to infection.

Acknowledgments

We thank Dr. Tony Williams from Aronex Pharmaceuticals, Inc. (The Woodlands, TX, 78381) for ensuring we had a continuous supply of Nyotran®. We also thank Dr. Mike Rinaldi for his advice during therapy. This is a SeaWorld San Antonio technical contribution number 2000-02-T

References

1.  Holland J. 1997b. Emerging zygomycoses of humans: Saksenaea vasiformis and Apophysomyces elegans. Curr. Top. Med. Mycol. 8: 27-34.

2.  Reidarson TH, J McBain. 1998c. Total nutritional support of two adult Commerson's dolphins (Cephalorhynchus commersoni). San Diego, California. 29th: 46.

3.  Reidarson TH, JM McBain, LM Dalton, MG Rinaldi. 1999a. Diagnosis and treatment of fungal infections in marine mammals. In: Fowler,M.E. and E.R.Miller (ed.). Zoo and Wild Animal Medicine. Current Therapy 4. W.B. Saunders, Philadelphia, PA. Pp. 478-85.