These infections result from inhalation of the spores of dimorphic fungi that have their mold forms in the soil. Within the lungs, the spores differentiate into yeasts or other specialized forms, such as spherules.
Most lung infections are asymptomatic and self-limited. However, in some persons, disseminated disease develops in which the organisms grow in other organs, cause destructive lesions, and may result in death. Infected persons do not communicate these diseases to others.
Important features of the systemic fungal diseases are described in Table 49–1. Systemic fungi are also called endemic fungi because they are endemic (localized) to certain geographic areas.
TABLE 49–1Important Features of Systemic Fungal Diseases |Favorite Table|Download (.pdf) TABLE 49–1 Important Features of Systemic Fungal Diseases
|Genus ||Form in Tissue Seen by Microscopy ||Geographic Location ||Important Clinical Findings ||Laboratory Diagnosis |
|Coccidioides ||Spherule ||Southwestern United States and Latin America ||Valley fever in immunocompetent; dissemination to bone and meninges in immunocompromised, pregnant women, African Americans, and Filipinos ||Culture at 20°C grows mold with arthrospores; serologic test for IgM and IgG |
|Histoplasma ||Yeasts within macrophages ||Ohio and Mississippi River valleys; worldwide; associated with bird and bat guano ||Cavitary lung lesions; granulomas in liver and spleen; pancytopenia and tongue ulcer in immunocompromised ||Culture at 20°C grows mold with tuberculate macroconidia; serologic test for IgM and IgG; urinary antigen |
|Blastomyces ||Yeasts with single broad-based bud ||Central and southeastern United States; Africa ||Ulcerated lesions of the skin ||Culture at 20°C grows mold |
|Paracoccidioides ||Yeasts with multiple buds ||Latin America, especially Brazil ||Ulcerated lesions of the face and mouth ||Culture at 20°C grows mold; serologic test for IgM and IgG |
Coccidioides immitis and C. posadasi cause coccidioidomycosis. The clinical manifestations of disease caused by these two species are the same, but the geographical distribution differs. For simplicity, the original species name, C. immitis, will be used most often in this chapter.
Coccidioides species are dimorphic fungi that exist as a mold in soil and as a spherule in tissue (Figure 49–1). C. immitis and C. posadasi are distinguished by genotyping but not by routine diagnostic tests in the clinical laboratory.
Stages of Coccidioides immitis. A: Arthrospores form at the ends of hyphae in the soil. They germinate in the soil to form new hyphae. If inhaled, the arthrospores differentiate into spherules. B: Endospores form within spherules in tissue. When spherules rupture, endospores disseminate and form new spherules. (Reproduced with permission from Brooks GF et al. Medical Microbiology. 20th ed. Originally published by Appleton & Lange. Copyright 1995, McGraw-Hill.)
Transmission & Epidemiology