Pathogenesis and spectrum of disease of Systemic Mycoses
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p746-747
2025-12-01
54
Traditionally, the systemic mycoses have included only blastomycosis, coccidioidomycosis, histoplasmosis, and paracoccidioidomycosis. Of the species that cause these disorders, only H. capsulatum and B. dermatitidis are genetically related. Although these fungi are morphologically dissimilar, they have one characteristic in common: dimorphism. Most of these organisms, except for C. immitis, are thermally dimorphic. The dimorphic fungi exist in nature as the mold form, which is distinct from the parasitic or invasive form, sometimes called the tissue form. Distinct morphologic differences may be observed with the dimorphic fungi both in vivo and in vitro, as discussed later in the chapter.
Blastomyces dermatitidis
B. dermatitidis commonly produces an acute or chronic suppurative and granulomatous infection. Blastomycosis begins as a respiratory infection and is probably acquired by inhalation of the conidia or hyphal fragments of the organism. The infection may spread and involve secondary sites of infection in the lungs, long bones, soft tissue, and skin.
Coccidioides immitis
Approximately 60% of patients with coccidioidomycosis are asymptomatic and have selflimited respiratory tract infections. However, the infection may become disseminated, with extension to visceral organs, meninges, bone, skin, lymph nodes, and subcutaneous tissue. Fewer than 1% of those who develop coccidioidomycosis ever become seriously ill; dissemination does occur, however, most frequently in individuals of darkskinned races. Pregnancy also appears to predispose women to disseminated infection. This infection has been known to occur in epidemic proportions. In 1992, an epidemic occurred in northern California, with more than 4000 cases seen in Kern County near Bakersfield. People who visit endemic areas and return to a distant location may present to their local physician; therefore, the endemic mycoses should be considered in the differential diagnosis if the patient has the appropriate travel history. All laboratories should be prepared to deal with the laboratory diagnosis of coccidioidomycosis.
Histoplasma capsulatum
H. capsulatum most commonly produces a chronic, granulomatous infection (histoplasmosis) that is primary and begins in the lung and eventually invades the reticuloendothelial system. Approximately 95% of cases are asymptomatic and selflimited, although chronic pulmonary infections occur. The disease can be disseminated throughout the reticuloendothelial system; the primary sites of dissemination are the lymph nodes, liver, spleen, and bone marrow. Infections of the kidneys and meninges are also possible. Resolution of disseminated infection is the rule in immunocompetent hosts, but progressive disease is more common in immunocompromised patients (e.g., patients with AIDS). Ulcerative lesions of the upper respiratory tract may occur in both immunocompetent and immunocompromised hosts.
Paracoccidioides brasiliensis
P. brasiliensis produces a chronic granulomatous infection (paracoccidioidomycosis) that begins as a primary pulmonary infection. It often is asymptomatic and then disseminates to produce ulcerative lesions of the mucous membranes. Ulcerative lesions are commonly present in the nasal and oral mucosa, gingivae, and less commonly the conjunctivae. Lesions occur commonly on the face in association with oral mucous membrane infection. The lesions are characteristically ulcerative, with a serpiginous (snakelike) active border and a crusted surface. Lymph node involvement in the cervical area is common. Pulmonary infection is frequently seen, and progressive chronic pulmonary infection is found in approximately 50% of cases. In some patients dissemination occurs to other anatomic sites, including the lymphatic system, spleen, intestines, liver, brain, meninges, and adrenal glands.
Penicillium marneffei
P. marneffei is an emerging pathogen that commonly infects immunosuppressed individuals. The organism causes either a focal cutaneous or mucocutaneous infection, or it may produce a progressive disseminated and frequently fatal infection. Granulomatous, suppurative, and necrotizing inflammatory responses have been demonstrated. The mode of transmission and the primary source in the environment are unknown, but the bamboo rat has been implicated.
Sporothrix schenckii
S. schenckii, also a dimorphic fungus, is often associated with chronic subcutaneous infection. The primary lesion begins as a small, nonhealing ulcer, often of the index finger or the back of the hand. With time, the infection is characterized by the development of nodular lesions of the skin or subcutaneous tissues at the point of contact and later involves the lymphatic channels and lymph nodes that drain the region. The subcutaneous nodules ulcerate to form an infection that becomes chronic. Only rarely is the disease disseminated. Pulmonary infection may be seen in patients that inhale the spores of S. schenckii.
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