Abstract
Mucormycosis (formerly zygomycosis) is a fungal infection which has an acute onset, and often results in a rapid death after minimal clinical signs appear. The fungal spores are found in soil, decaying wood and other organic material. Unlike most pathogenic forms of Mucorales, which infects immunocompromised individuals, the fungus formally known as Apophysomyces elegans has the ability to infect immunocompetent individuals. This fungus has been further studied and is now considered one of three new species, Apophysomyes ossiformis, Apophysomyes variabilis, and Apophysomyces trapeziformis.1 It can occur in cluster infections after natural disasters; the most recent cluster of human infections occurred after a tornado struck Joplin, Missouri in May of 2011.2 Historically, dolphins diagnosed with mucormycosis have not survived this disease despite treatment.3,4
Clinical presentation most commonly is limited to anorexia, severely elevated erythrocyte sedimentation rate and/or fibrinogen levels and accompanied by only mild increases in the white blood cell counts. This presentation would be considered "occult" mucormycosis. Occasionally, eschar skin lesion(s) develop on some patients, allowing for tissue histology with special silver stains to provide a probable diagnosis consistent with a mucormycete. A definitive diagnosis requires fungal culture and species identification. These fungi require specific culture techniques and the laboratory used should be familiar with these.
A new azole, posaconazole, had shown promise in treatment of mucormycosis in human patients. Posaconazole (Noxafil) is a triazole that is structurally related to itraconazole. As with all azole antifungal agents, posaconazole works principally by inhibition of cytochrome P450 14a-demethylase (P45014DM). This enzyme is in the sterol biosynthesis pathway that leads from lanosterol to ergosterol. Prior to the development of posaconazole, various treatments were attempted without success. Posaconazole along with aggressive surgical removal of infected tissue, when possible, has proven to be effective in treating this disease.5
Because of the occult nature of this disease, this drug, by necessity, is used on a diagnostic "educated guess." The problem with this approach is twofold. Number one, it is not known how long to treat the patient. In the cases where initial treatment was effective, but when treatment was discontinued prematurely, the disease reoccurred with a fatal outcome.6 The other practical problem with this approach is the expense of using posaconazole. The cost to treat a 200-kg dolphin at a dose of 5 mg/kg BID is close to $9,000.00 U.S. a month, with treatment lasting several months to a year or more.
Fortunately, some of these problems may be resolved with a new diagnostic test being developed at Auburn University, College of Veterinary Medicine. Dr. Joe Newton, a veterinary pathologist at AUCVM, was involved in the collaborative research and development of a serum assay for the detection of equine pythiosis, caused by the oomycetous pathogen Pythium insidiosum, and for the development of an immunotherapeutic "vaccine" for the treatment of pythiosis in horses.7,8 A similar assay and vaccine are used to help in the diagnosis and treatment of canine pythiosis, which, like mucormycosis in cetaceans, often has an occult presentation.9 Auburn University was contacted last winter and the mucormycosis problem in cetaceans was discussed. Although these organisms are different, there was a thought that a blood test to diagnose these "occult" mucormycosis cases and monitor treatment response may be possible. With the cooperation of The University of Texas Health Science Center at San Antonio supplying the cultures of Apophysomyces trapeziformis, the initial studies have been possible. Fortunately, serum had been saved from previously documented cases of mucormycosis and has been used in the initial series testing. The results from preliminary work are very encouraging.
Acknowledgements
The authors wish to thank Priscilla Barger and Dr. Joe Newton, Auburn University, College of Veterinary Medicine, Department of Pathobiology, Auburn, Alabama for listening to our requests and having the understanding of the importance of this disease to those of us in the marine mammal community. Deanna Sutton, Annette Fothergill and Dr. Rinaldi, South Texas Reference Laboratory, Fungus Testing Laboratory, University of Texas Health Science Center at San Antonio provided high quality diagnostic testing of these difficult cases over many years. Dr. Blanchard and the laboratory technicians of the Fort Walton Medical Center, Fort Walton Beach, Florida, provided rapid tissue processing for early diagnosis. And Schering Plough supplied the posaconazole in the early cases under the compassionate need requirements.
References
1. Alvarez E, Stchigel A, Cano J, et al. Molecular phylogenetic diversity of the emerging murcoralean fungus Apophysomyces: proposal of three new species. Rev Iberoam Micol. 2010;27: 80–90.
2. Benedict K, AdebanjoT, et al. Fatal fungal soft-tissue infections after a tornado - Joplin, Missouri. Morbidity and Mortality Weekly Report. 2011;60(29):992.
3. Townsend FI, Materese FJ, Sips DG. The use of amphotericin-B in the therapy of systemic zygomycosis. In: IAAAM 27th Annual Conference Proceedings, Chattanooga, TN; 1996:22.
4. Robeck TR, Dalton LM. Saksenaea vasiformis and Apophysomyces elegans zygomyctotic infections in bottlenose dolphins (Tursiops truncatus), a killer whale (Orcinus orca), and pacific white-sided dolphins (Lagenorhynchus obliquidens). J Zoo Wildlife Med. 2002;33(4):356–366.
5. Townsend FI, Williams A, Staggs L. The successful treatment of systemic zygomycosis in a bottlenose dolphin (Tursiops truncatus) calf. In: IAAAM 37th Annual Conference Proceedings, Nassau, Bahamas; 2006;37:113–114.
6. Wells R, Townsend FI, Rotstein D. Tracheal zygomycosis presenting as stridor and partial upper airway obstruction in a pantropical spotted dolphin (Stenella attentuata). In: IAAAM 42nd Annual Conference Proceedings, Las Vegas, NV; 2011:175.
7. Mendoza L, Kaufman L, Mandy W, Glass R. Serodiagnosis of human and animal pythiosis using an enzyme-linked immunosorbent assay. Clin Diagn Lab Immunol. 1997;4:715–718.
8. Mendoza L, Newton JC. Immunology and immunotherapy of the infections caused by Pythium insidiosum. Med Mycol. 2005;43:477–486.
9. Grooters A, Leise N, Lopez M, O'Reilly K. Development and evaluation of an enzyme-linked immunosorbent assay for serodiagnosis of pythiosis in dogs. J Vet Intern Med. 2002;16:142–146.