Abstract

An adult male zebra shark, Stegostoma fasciatum, presented with a markedly swollen right clasper. The shark had been by himself in a reserve tank for the prior 13 months due to chronic tankmate aggression. The clasper was swollen, with injected skin capillaries and multifocal, coalescing, purple, raised lesions. Repeated physical examination, fine needle aspirates, biopsies, bacterial and fungal cultures did not reveal an etiology, only locally extensive granulomatous inflammation. Treatment with antimicrobials was ineffective. On the third round of biopsies, special stains on deep edges of a soft tissue swelling that developed adjacent to the affected clasper confirmed branching fungal elements. Panfungal PCR was positive and a 200 bp DNA fragment sequence was compatible with an Ascomycota. A pure culture of the fungus yielded a 50 bp amplicon from 18s rRNA sequencing that demonstrated 99% homology to Metarhizium anisopliae (GenBank JN13140.1). Voriconazole^a therapy was started at 5.32 mg/kg PO q 48 h based on prior successful treatment of fusariosis in a bonnethead but was eventually titrated to an effective dosing regimen of 10.64 mg/kg PO SID based on serum testing.³ Transition to generic formulation^b after 2 months of therapy did not impact serum levels or efficacy. Therapy was continued for 9 months with full resolution of signs. Metarhizium anisopliae is an entomopathogenic fungus that is commonly used commercially as a biopesticide, though not at the Shedd Aquarium.^15,16 This agent is not considered a risk to humans or laboratory animals; however, there are emerging reports of infections in both humans and animals.^1,2,4-14

Endnotes

a. Vfend, 200-mg tablets, Pfizer Ireland Pharmaceuticals, Ringaskiddy, County Cork, Ireland
b. Voriconazole, 200-mg capsules, Diamondback Drugs, Scottsdale, AZ, USA

Acknowledgments

The authors wish to thank the incredible efforts of the staff of the Shedd Aquarium’s Animal Health Department as well as the extraordinary aquarists in the Fishes Department, most notably Lise Watson and Heather Thomas for their tireless work on this case. We would also like to thank the experts in the University of Illinois Veterinary Diagnostic Laboratory and Zoological Pathology Program as well as the Fungus Testing Laboratory at the University of Texas Health Science Center for their consultation and work on the identification of the pathogen.

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