Abstract
An approximately 144-kg, female, bottlenose dolphin, Tursiops truncatus, presented for anorexia on November 26, 2010. She had an elevated erythrocyte sedimentation rate (ESR) of 30 mm/hr (normal 4–10), a low serum iron 60 µg/dL (normal 165–294), and a mildly elevated neutrophilic leukocytosis 12,000 cells/µl (normal 5,000–9,500). Serum immunodiffusion assays (Cerodex Laboratories, Inc.) for Candida and Aspergillus 4G were positive; however, serum FungitellTM (Beacon Diagnostics Laboratory) and galactomannan assays (MiraVista Diagnostics) for Aspergillus sp. antigen were negative. She had been diagnosed with Aspergillus sp. fungal pneumonia in September 2007, so she was treated empirically for fungal infection despite these conflicting results. She was initially treated with itraconazole beginning on the first day of illness, but her sedimentation rate continued to rise (62 mm/hr). On day 6 she was changed to posaconazole (Noxafil) 720 mg (5 mg/kg) twice daily in order to treat a suspected occult mucormycosis (formerly zygomycosis). Apophysomyces species are responsible for most mucormycotic fungal infections identified in the Florida panhandle and are rapidly progressive and usually fatal. Animals that have survived have been successfully treated with posaconazole.3 In response to the medication change, her sedimentation rate gradually decreased, becoming normal (≤ 10 mm/hr) on day 46, at which time her posaconazole dose was decreased to 720 mg (5 mg/kg) once daily. Therapeutic drug monitoring was utilized to insure adequate plasma posaconazole concentrations were maintained throughout the course of treatment. Plasma levels in this individual ranged from 1.19–5.15 µg/ml (n = 18) within the in vitro MIC90 (1–4 µg/ml) for posaconazole against zygomycetes.2 It was questioned how long treatment should be continued, as animals previously treated for mucormycosis succumbed to the disease after posaconazole was discontinue prematurely.1
On day 237 of treatment, with the development of an experimental ELISA for the detection of Apophysomyces sp., diagnostic serum samples were evaluated from prior to her illness and on the ninth day of illness. Her titer was negative (13% of positive control) 8 months prior to her illness and positive (233% of positive control) on the ninth day of illness. A diagnosis of occult mucormycosis was confirmed. Additional samples (n = 16) were analyzed from throughout her treatment course in which she appeared to clinically respond. Her antibody titers fell from positive (233%) on day 9, to suspect positive (57%) on day 102, to negative (29.5%) on day 183. This was in direct correlation with duration of treatment with posaconazole, her declining erythrocyte sedimentation rates and normalizing serum iron levels. Her most recent titer remains negative (9.5%) on day 370. It is interesting to note that although she was clinically normal (ESR 4, serum iron 208) on day 68, her titer against Apophysomyces sp. was still positive (106% of positive control).
This new ELISA, although still under development, has the potential to diagnose occult mucormycosis caused by Apophysomyces related fungal species, to guide the practitioner in monitoring treatment, and to provide long-term monitoring of recurrence of subclinical disease. Serum Apophysomyces sp. titers will continue to be monitored in this individual via ELISA for recurrence of disease while the posaconazole dose is decreased and eventually discontinued.
Acknowledgements
The authors wish to thank the trainers at Florida's Gulfarium for assisting us in collecting diagnostic samples and for providing excellent care to their animals. The authors thank the Fungus Testing Laboratory at University of Texas, San Antonio, for performing the posaconazole plasma drug levels.
References
1. Brudek-Wells RL, Townsend FI, Rotstein D. Tracheal zygomycosis presenting as stridor and partial upper airway obstruction in a pantropical spotted dolphin (Stenella attenuata). In: IAAAM 42nd Annual Conference Proceedings, Las Vegas, NV; 2011:175.
2. Groll AH, Schrey D. The current role of posaconazole in managing zygomycosis. Curr Fungal Infect Rep. 2011;5:29–33.
3. Townsend FI, Williams A, Staggs L. Successful treatment of systemic zygomycosis in a bottlenose dolphin (Tursiops truncatus) calf. In: IAAAM 37th Annual Conference Proceedings, Nassau, Bahamas; 2006:113–114.