Systemic Mycoses
Dr.HudaThese 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.
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.
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COCCIDIOIDE
HISTOPLASMABLASTOMYCES
PARACOCCIDIOIDES
Systemic Mycoses
COCCIDIOIDE
COCCIDIOIDEDisease Coccidioides immitis causes coccidioidomycosis. Properties C. immitis is a dimorphic fungus that exists as a mold in soil and as a spherule in tissue
Transmission & Epidemiology Coccidioide
The fungus is endemic in arid regions of the southwestern United States and Latin America. . In soil, it forms hyphae with alternating arthrosporesArthrospores are very light and are carried by the wind. They can be inhaled and infect the lungs.
Pathogenesis of Coccidioide
In the lungs, arthrospores form spherules that are large, have a thick, doubly refractive wall, and are filled with endospores. Upon rupture of the wall, endospores are released and differentiate to form new spherules. The organism can spread within a person by direct extension or via the bloodstream. Granulomatous lesions can occur in virtually any organ but are found primarily in bones and the central nervous system (meningitis) Dissemination from the lungs to other organs occurs in people who have a defect in cell-mediated immunity.Clinical Findings of Coccidioide
Infection of the lungs is often asymptomatic and is evident only by a positive skin test and the presence of antibodies. Some infected persons have an influenza like illness with fever and cough. About. 50% have changes in the lungs (infiltrates, adenopathy, or effusions) as seen on chest x-ray. 10% develop erythema nodosum or arthralgias. This syndrome is called "valley fever" or "desert rheumatism"; it tends to subside spontaneously. Disseminated disease can occur in almost any organ; the meninges, bone, and skin are important sites.*
Coccidioidomycosis lesions in subcutaneous tissue
Figure 22.9Laboratory Diagnosis of Coccidioide
Spherules of Coccidioides immitisFigure 22.8
Laboratory Diagnosis of Coccidioide
In infected persons, skin tests with fungal extracts cause at least a 5mm induration 48 hours after injection (delayed hypersensitivity reaction). Skin tests become positive within 2-4 weeks of infection and remain so for years but are often negative in patients with disseminated disease. In general, a person who has a positive skin test reaction has developed sufficient immunity to prevent disseminated disease from occurring.Treatment & Prevention of Coccidioide
No treatment is needed in asymptomatic or mild primary infection. Amphotericin B (Fungizone) or Itraconazole is used for persisting lung lesions or disseminated disease. Ketoconazole is also effective in lung disease. Fluconazole is the drug of choice for meningitis. There are no means of prevention except avoiding travel to endemic areas.HISTOPLASMA
Properties of Histoplasma
H. capsulatum ,the causative agents is a dimorphic fungus that exists as a mold in soil and as a yeast in tissue. It forms two types of asexual spores (1) tuberculate macroconidia, with typical thick walls and fingerlike projections that are important in laboratory identification, (2) microconidia, which are smaller, thin, smooth walled spores that, if inhaled, transmit the infection.
Transmission & Epidemiology of Histoplasma
This fungus occurs in many parts of the world. In the United States it is endemic in central and eastern states, especially in the Ohio and Mississippi River valleys. It grows in soil, particularly if the soil is heavily contaminated with bird droppingsPathogenesis & Clinical Findings of Histoplasma
Inhaled spores are engulfed by macrophages and develop into yeast forms. In tissues, H. capsulatum occurs as an oval budding yeast inside macrophagesPathogenesis & Clinical Findings of Histoplasma
With intense exposure (eg, in a chicken house or bat infested cave), pneumonia may become clinically manifest. The organisms spread widely throughout the body; especially to the liver and spleen, Severe disseminated histoplasmosis develops in a small minority of infected persons with a reduced cell-mediated immunity, such as AIDS patients.*
Histoplasmosis
Usually asymptomatic and resolves without damage Clinical histoplasmosis results in one of four diseases Chronic pulmonary histoplasmosis Chronic cutaneous histoplasmosis Systemic histoplasmosis Ocular histoplasmosisZarqa Private UniversityBiology 4223 – The Fungi Disseminated Histoplasma capsulatum, skin infection.
Laboratory Diagnosis of Histoplasma
Zarqa Private UniversityBiology 4223 – The Fungi Histoplasma capsulatumLaboratory Diagnosis of Histoplasma
Serological tests A skin test using histoplasmin (a mycelial extract) becomes positive, within 2-3 weeks after infection . However,false-positive reactions (due to cross-reactivity) and many false-negative reactions (in disseminated disease) Radioimmunoassay CF test (cross-reactions with other fungi, especially Blastomyces can occur) ID test detects precipitating antibodies (precipitins)An antibody titer of 1:32 in the with yeast phase antigens is considered to be diagnostic. However,. CF titers fall when the disease becomes inactive and rise in disseminated disease. The by forming two bands, M and H, in an agar-gel diffusion assay. The ID test is more specific but less sensitive than the CF test.
Treatment & Prevention of Histoplasma
Same as in coccidioidomycosis.BLASTOMYCES
Disease of Blastomyces
Blastomyces dermatitidis causes blastomycosis, known as North American blastomycosis.
Properties of Blastomyces
B. dermariridis is a dimorphic fungus that exists as a mold in soil and as a yeast in tissue. The yeast is round with a doubly refractive wall and a single broad-based budNote that this organism forms a broad-based bud, whereas Cryptococcus neoformans is a yeast that forms a narrow-based bud.
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Transmission & Epidemiology of Blastomyces
This fungus is endemic primarily in eastern North America, especially in the region bordering the Ohio, Mississippi, It grows in moist soil rich in organic material, forming hyphae with small pear-shaped conidia. Inhalation of the conidia causes human infection.Pathogenesis & Clinical Findings of Blastomyces
Infection occurs mainly via the respiratory tract. Asymptomatic or mild cases are rarely recognized. Dissemination may result in ulcerated granulomas of skin, bone, or other sites.Cutaneous blastomycosis
Figure 22.6Laboratory Diagnosis of Blastomyces
In tissue biopsy specimens, thick-walled yeast cells with single broad-based buds are seen microscopically. Hyphae with small pear-shaped conidia are visible on culture. The skin test lacks specificity and has little value. Serologic tests have little value.Treatment & Prevention of Blastomyces
Itraconazole is the drug of choice for most patients Amphotericin B should be used to treat severe disease. Surgical excision may be helpful. There are no means of prevention.PARACOCCIDIOIDES
Disease of ParacoccidioidesParacoccidioides brasiliensis causes paracoccidioidomycosis, also known as South American blastomycosis.