The respiratory tract is the primary mode of entry for the Zygomycetes. Pulmonary infections usually occur in the immunocompromised patient and resemble those caused by the aspergillus spp. Risk factors include hematologic problems, ketoacidosis, long- term immunosuppressive therapy, and underlying lung disease. Needle aspirates or biopsy specimens provide the best yield for diagnosis. Tissue specimens should not be ground, but rather minced or cut up into small bits for inoculation to media, grinding may render the organisms nonviable and difficult to detect in smears.
Histopathologic evaluation usually shows broad, nonseptate, hyaline hyphae, 7 to 15 microns in width and with either irregular branching or branching at 90-degree angles. Isolation is achieved fairly easily on most fungal media such as Potato dextrose agar, malt agar, or Czapek agar. Rhizopus is the most common;y isolated genus from human specimens, followed by Absidia and Rhizomucor. These three make up around 85% of all isolates. Identification of Zygomycetes is based on examination of the asexual morphology.
Direct examination of scrapings and biopsy and other specimens is important for diagnosis. Tissue specimens should be stained promptly with Gomorri’s methenamine silver and with hematoxylin and eosin stains. In addition, a portion should be examined on a slide with 20% aqueous KOH with calcofluor under flurescent microscope.