1. Chapter 20

2. How do Fungi Cause Disease?
The tissue damage associated with fungal infections results primarily from direct invasion of tissue, with subsequent displacement and destruction of vital structures, coupled with toxic effects of the inflammatory response.
Masses of fungal cells can cause obstruction of bronchi in the lungs and tubules and ureters in kidneys, leading to obstruction of the flow of bodily fluids.
Some fungi can grow in the walls of arteries and veins, leading to occlusion and tissue necrosis resulting from a lack of oxygen.

3. Classification of Fungal Diseases
Fungal infections (mycoses) can be classified into the following four categories:
Superficial mycoses—fungal infections of the outermost areas of the body (outer surfaces of hair shafts, the epidermis)
Cutaneous, hair, and nail mycoses (tinea or “ringworm” infections)
Subcutaneous mycoses
Systemic mycoses—the most serious types of fungal infections

4. Fungal Infections of the Skin
Dermatophytosis (Tinea [“Ringworm”] Infections, Dermatomycosis)
Caused by various species of filamentous fungi, including Microsporum, Epidermophyton, and Trichophyton spp.
These fungi are collectively referred to as dermatophytes.
Note that ringworm infections have nothing to do with worms.

5. Fungal Infections of the Lower Respiratory Tract
Coccidioidomycosis (Valley Fever)
Coccidioides immitis, a dimorphic fungus; transmission occurs via inhalation of arthrospores
Cryptococcosis
Two subspecies of Cryptococcus neoformans, an encapsulated yeast; transmission occurs via inhalation of yeasts
Histoplasmosis
Histoplasma capsulatum var. capsulatum, a dimorphic fungus; transmission occurs via inhalation of conidia from soil

6. Fungal Infections of the Lower Respiratory Tract (cont.)
Pneumocystis Pneumonia (PCP; Interstitial Plasma-Cell Pneumonia)
Caused by Pneumocystis jiroveci, which has both protozoal and fungal properties
Was once classified as a protozoan, but is now classified as a fungus
Mode of transmission is unknown; perhaps direct contact, transfer of pulmonary secretions from infected to susceptible persons, or perhaps airborne

7. Fungal Infections of the Oral Cavity
Thrush
A yeast infection of the oral cavity
Common in infants, elderly patients, and immunosuppressed individuals
White, creamy patches occur on the tongue, mucous membranes, and the corners of the mouth
Caused by Candida albicans and related species

8. Yeast Vaginitis Most cases are caused by the yeast, Candida albicans
Can be diagnosed by microscopic examination of a saline wet mount of vaginal discharge material, in which numerous yeasts and hyphae may be observed
The mere presence of yeast is not proof of yeast vaginitis, as the vaginal flora of up to 25% of healthy women can contain Candida spp.

9. Cryptococcal Meningitis
Can be caused by three subspecies of Cryptococcus neoformans, an encapsulated yeast
Cryptococcosis starts as a lung infection, but spreads via the bloodstream to the brain
Cryptococcal meningitis can be presumptively diagnosed by observing encapsulated, budding yeasts in CSF specimens examined by an India ink preparation