Chapter Capsule

A. Microscopic fungi (molds and yeasts) are widespread in nature. A few members cause fungal diseases or mycoses.

B. Infectious fungi occur in groups based upon the virulence of the pathogen and the level of involvement, whether systemic, subcutaneous, cutaneous, or superficial.

C. True or primary pathogens have virulence factors that allow them to invade and grow in a healthy host.

1. They are also thermally dimorphic, occurring as hyphae in their natural habitat and converting to yeasts while growing as parasites at body temperature (37°C).

2. Inhaled spores initiate primary pulmonary infection (PPI), which can spread to the skin and other systems.

3. Diseases are not transmissible, and cause a long-term allergic reaction to fungal proteins.

4. True pathogens are endemic to certain geographic areas.

D. Opportunistic fungal pathogens are normal flora or common inhabitants of the environment that invade mainly patients whose host defenses are compromised.

1. They are only weakly virulent and lack thermal dimorphism.

2. Infections may be local, cutaneous, or systemic, and are currently on the rise, due to more weakened patients.

E. Some pathogens such as the dermatophytes (skin fungi) can infect healthy people, are not highly invasive, and are transmissible.

F. Immunity to fungal infections consists primarily of nonspecific barriers, inflammation, and cell-mediated defenses. Antibodies may be used to detect disease in some cases.

G. Diagnosis and identification require microscopic examination of stained specimens, culturing of pathogen in selective and enriched media, and specific biochemical and in vitro serological tests. Skin testing for true and opportunistic pathogens can determine prior disease but is not useful in diagnosis.

H. Control of fungal infections involves drugs such as intravenous amphotericin B, flucytosine, azoles (fluconazole), and nystatin. No useful vaccines exist.

A. Histoplasmosis (Ohio Valley fever): The agent is Histoplasma capsulatum, distributed worldwide, but most prevalent in eastern and central regions of the United States.

1. Infection is related to the disturbance of soil and animal excreta.

2. Inhaled conidia produce primary pulmonary infection that may progress to systemic involvement of a variety of organs and chronic lung disease.

B. Coccidioidomycosis (Valley fever): Coccidioides immitis has blocklike arthroconidia in the free-living stage and spherules containing endospores in the lungs.

1. The agent lives in alkaline soils in semiarid, hot climates, and is endemic to the southwestern United States.

2. Infection occurs when arthrospores are inhaled from dust. Growth in the lungs creates spherules and nodules; disseminated infection is debilitating.

C. Blastomycosis (Chicago disease): The agent is Blastomyces dermatitidis, a free-living species distributed in soil of a large section of the midwestern and southeastern United States.

1. Inhaled conidia convert to yeasts and multiply in lungs.

2. The inflammatory response produces cough and fever. Disease may progress to chronic cutaneous, bone, and nervous system complications.

D. Paracoccidioidomycosis (South American blastomycosis): Paracoccidioides brasiliensis is distributed in various regions of Central and South America. Lung infection occurs through inhalation or inoculation of spores, and systemic disease is not common.

A. Sporotrichosis (rose-gardener’s disease) is caused by Sporothrix schenckii, a free-living fungus that accidently infects the appendages and lungs. The lymphocutaneous variety occurs when contaminated plant matter penetrates the skin and the pathogen forms a local nodule, then spreads to nearby lymph nodes.

B. Chromoblastomycosis is a deforming, deep infection of the tissues of the legs and feet by soil fungi that enter a traumatic injury.

C. Mycetoma is a progressive, tumorlike disease of the hand or foot due to chronic fungal infection; may lead to loss of the body part.

A. Dermatophytoses are known as tinea, ringworm, and athlete’s foot. They are caused by species in the genera Trichophyton, Microsporum, and Epidermophyton, all of which are adapted to keratinized epidermis (skin, hair, nails).

B. Infections are communicable among humans, animals, and soil; infection is facilitated by moist, chafed skin; inflammatory reactions to fungi cause itching and pain.

1. Ringworm of scalp (tinea capitis) affects scalp and hair-bearing regions of head; hair may be lost. Ringworm of body (tinea corporis) occurs as inflamed, red ring lesions anywhere on smooth skin. Ringworm of groin (tinea cruris) affects groin and scrotal regions.

2. Ringworm of foot and hand (tinea pedis and tinea manuum) is spread by exposure to public surfaces; occurs between digits and on soles. Ringworm of nails (tinea unguium) is a persistent colonization of the nails of the hands and feet that distorts the nail bed.

C. Superficial mycoses affect the outermost epidermal structures. Tinea versicolor causes mild scaling, mottling of skin; white piedra is whitish or colored masses on the long hairs of the body; and black piedra causes dark, hard concretions on scalp hairs.

A. Candidiasis is caused by Candida albicans and other Candida species, common yeasts that normally reside in the mouth, vagina, intestine, and skin.

B. Infection predominates in cases of lowered resistance (babies, pregnancy, drug therapy, AIDS) and arises from normal flora or is transmissible through intimate contact.

1. Thrush occurs as a thick, white, adherent growth on the mucous membranes of mouth and throat.

2. Vulvovaginal yeast infection is a painful inflammatory condition of the female genital region that causes ulceration and whitish discharge.

3. Cutaneous candidiasis occurs in chronically moist areas of skin and in burn patients.

C. Cryptococcosis is caused by Cryptococcus neoformans, a widespread encapsulated yeast that inhabits soils around pigeon roosts; common infection of AIDS, cancer, or diabetes patients.

1. Infection of lungs leads to cough, fever, and lung nodules.

2. Dissemination to meninges and brain can cause severe neurological disturbance and death.

D. Pneumocystis carinii is a small, unicellular fungus that causes PCP, the most prominent opportunistic infection in AIDS patients. This form of pneumonia forms secretions in the lungs that block breathing and can be rapidly fatal if not controlled with medication.

E. Aspergillosis is caused by Aspergillus, a very common airborne soil fungus. Inhalation of clouds of spores causes fungus balls in lungs, and it can also cause invasive disease in the eyes, heart, and brain.

F. Mucormycosis is caused by molds in genus Rhizopus and Mucor. These usually harmless air contaminants invade the membranes of the nose, eyes, and brain of people with acidotic (diabetes, malnutrition), with severe consequences.