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Histoplasmosis due to Histoplasma duboisii
African histoplasmosis. Contrast with North American histoplasmosis due to Histoplasma capsulatum
Histoplasmosis due to Histoplasma duboisii is a mycotic infection primarily involving cutaneous, liver, lung, lymphatic, subcutaneous, and bony tissues. Skin and bone are the most frequently invaded sites [454]. The etiologic agent grows as a large yeast within giant cells. It may also present with small cells that are typical of those seen in histoplasmosis due to Histoplasma capsulatum. Nodular and ulcerative cutaneous and osteolytic lesions of bone that disseminate or remain localized are the primary clinical characteristics of histoplasmosis duboisii [11, 1185, 1186, 2101].
Special resource: You may also want to refer to the Infectious Disease Society of America-Mycoses Study Group (IDSA-MSG) Practice Guidelines for this disease. It is available at the IDSA website.
Isolated lesions may heal spontaneously. Surgical management is also an option. Disseminated disease has a grave prognosis, especially if the liver and spleen are involved. Amphotericin B, itraconazole or fluconazole are the drugs of choice [6, 36, 1690, 2302].
Minimal cellular reaction to the fungi is noted with the exception of large numbers of giant cells (up to 80 µm) and macrophages. Neutrophils are usually present, especially during necrosis. The globose to ovoid, thick-walled yeasts are 7-15 µm (average 10 µm) in diameter and may form rudimentary pseudohyphae consisting of 4 or 5 cells. Large aggregates of yeast cells can be readily seen within giant cells and extracellularly following necrosis of the host tissue. Unlike Blastomyces dermatitidis, the blastoconidia are not attached to the parent cell by a broad neck.
Direct examination
Clinical specimens such as tissue are examined in 10% KOH or calcofluor. The large yeast cells should be readily visible. Care must be taken to ensure that B. dermatitidis is not confused with the etiologic agent of histoplasmosis duboisii since they both occur in Africa.
Isolation
Inoculate the clinical material onto Inhibitory Mould Agar and/or yeast extract-phosphate agar and/or BHI agar with 10% sheep blood and/or a medium containing cycloheximide. Incubate cultures at 30°C and do not discard until 12 weeks.
Laboratory confirmation
Confirmation is necessary to ensure that the fungus is not a species of Chrysosporium or Sepedonium. This can be accomplished by the mould to yeast conversion, exoantigen technique or DNA probes. The etiologic agents of histoplasmosis capsulati and histoplasmosis duboisii are morphologically identical at 30°C and by DNA testing and exoantigen confirmation.
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Yeast Phase of Histoplasma capsulatum var duboisii, GMS stain
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References
6. Abrucio Neto, L., M. D. Takahashi, A. Salebian, and L. C. Cuce. 1993. African histoplasmosis. Report of the first case in Brazil and treatment with itraconazole. Rev Inst Med Trop Sao Paulo. 35:295-9.
11. Adekeye, E. O., M. B. Edwards, and H. K. Williams. 1988. Mandibular African histoplasmosis: imitation of neoplasia or giant-cell granuloma? Oral Surg Oral Med Oral Pathol. 65:81-4.
36. Akpuaka, F. C., H. C. Gugnani, and L. M. Iregbulam. 1998. African histoplasmosis: report of two patients treated with amphotericin B and ketoconazole. Mycoses. 41:363-364.
454. Cockshott, W. P., and A. O. Lucas. 1964. Histoplasmosis duboisii. Quart. J. Med. 33:223-238.
1185. Khalil, M., A. R. Iwatt, and H. C. Gugnani. 1989. African histoplasmosis masquerading as carcinoma of the colon. Report of a case and review of literature. Diseases of the Colon & Rectum. 32:518-520.
1186. Khalil, M. A., A. W. Hassan, and H. C. Gugnani. 1998. African histoplasmosis: report of four cases from northeastern Nigeria. Mycoses. 41:293-295.
1690. Onwuasoigwe, O. 1999. Fluconazole in the therapy of multiple osteomyelitis in African histoplasmosis. Int Orthop. 23:82-4.
2101. Shoroye, A., and G. A. Oyedeji. 1982. African histoplasmosis presenting as a facial tumour in a child. Ann Trop Paediatr. 2:147-9.
2302. Velho, G. C., J. M. Cabral, and A. Massa. 1998. African histoplasmosis: therapeutic efficacy of itraconazole. J Eur Acad Dermatol Venereol. 10:77-80.
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