Abstract

The death of two immunocompetent Atlantic bottlenose dolphins subsequent to hemorrhagic encephalitis caused by angioinvasive zygomycosis resulted in an attempt at prophylaxis for the remaining seven dolphins housed in the same pool. Two separate environmental samples were culture positive for Apophysomyces elegans. This fungus is a soil inhabitant that has been reported in warm and tropical climates. Recent reports of human infections with this fungal species have included immunocompetent individuals. Skin and soft tissue infections are one of the manifestations of this disease in dolphins and humans following wound contamination. Angioinvasiveness has been reported in as little as seven days following a deep wound contamination in a person. While diagnostics and treatment have improved, some deaths have still been reported even after extensive surgical debridement and treatment with liposomal amphotericin B or liposomal nystatin in both dolphins and people. A second serious clinical manifestation is dissemination inhalation that results in a hemorrhagic encephalitis from aggressive angioinvasiveness of the fungal organisms. This clinical manifestation has not been reported in the human literature and does not allow for the primary treatment of extensive surgical debridement.

Two adult dolphins housed in a group of nine in a 1.9 million gallon pool presented with severe central neurological signs. These included unilateral body paralysis, unilateral and bilateral loss of vision, and tremor activity. The first dolphin, a young adult dominant male, died within twenty-four hours of displaying any abnormal behavior. The second dolphin, a lactating female, died six days later. On histopathology both dolphins had zygomyces organisms destroying the cerebral vessel architecture. The male also had the same zygomyces organisms on plaques found in his bronchi. All remaining dolphins, ranging from one to twelve years of age, were started on ciprofloxacin at 6 mg/kg BID and fluconazole 1 mg/kg SID. At the onset of the first abnormal lab data, a fibrinogen of 600 mg/dl in a young female, all seven dolphins were also placed on terbinafine at 2 mg/kg SID. The treatment continued for six weeks.

The Apophysomyces elegans isolate was used for sensitivity testing. The MIC value for terbinafine was surprisingly low at 0.125 mg/ml at 48 hours and synergistic with fluconazole at 0.06 mg/ml at 48 hours. Fluconazole by itself was not effective. Terbinafine serum levels were randomly done on the dolphins during their course of treatment. The terbinafine dose at 2 mg/kg SID showed sufficient therapeutic levels (mean 1694 ng/ml) based on human data. Lab values for the dolphins were monitored during the course of treatment. The only abnormal results were elevated liver enzymes in one dolphin on week six of the treatment. These values returned to normal one month after treatment was discontinued. The one-year-old dolphin was not trained for blood draws but never exhibited any clinical signs during the course of the treatment.

Terbinafine is a fungicidal drug that has been extensively used in human dermatophyte infections. It has only been available in the United States in recent years. It has been shown to be synergistic with other antifungal agents and in vitro data suggests the potential in therapy for severe fungal infections. In this small group of dolphins, terbinafine appears to be well tolerated for an extended period of time for dolphins of various ages. Monitoring liver enzymes during the course of treatment appears to be advisable. Further in vivo and combination testing for this rapidly fatal fungus and antifungal agent are recommended.

Acknowledgements

We are very grateful to Dr. Tom Reiderson Sea World San Diego, Dr. Forrest Townsend, University of Texas Fungal Diagnostic lab, Novartis, and CDC.