Fungi and Human Disease

Humans have a high level of innate immunity to fungi and most of the infections they cause are mild and self-limiting.

This resistance is due to:

When fungi do pass the resistance barriers of the human body and establish infections, the infections are classified according to the tissue levels initially colonized.

A. Superficial mycoses- infections limited to the outermost layers of the skin and hair.

Disease Etiological Agent Symptoms Identification of Organism
Pityriasis versicolor Malassezia furfur hypopigmented macules  Spaghetti and meatballs appearance of organims in skin scrapings. 
Tinea nigra  Exophiala werneckii black macules Black, 2-celled oval yeast in skin scrapings
Black piedra Piedraia hortai black nodule on hair shaft black nodule on hair shaft composed of spore sacs and spores
White piedra Trichosporon beigelii creme-colored nodules on hair shaft white nodule on hair shaft composed of mycelia that fragment into arthrospores
B. Cutaneous mycoses- infections that extend deeper into the epidermis, as well as invasive hair and nail diseases.

These diseases are restricted to the keritinized layers of the skin, hair, and nails. Unlike the superficial mycoses, host immune responses may be evoked, resulting in pathologic changes expressed in the deeper layers of the skin. The organisms that cause these diseases are called dermatophytes. These diseases are often called ringworm or tinea. All the following diseases are causes by Microsporum, Trichophyton, and Epidermophyton, which comprise 41 species.

Disease Symptoms Identification of organism
Tinea capitis ringworm of scalp presence/absence and shape of micro- and macroconidia in scrapings of lesion, KOH mount
Tinea corporis ringworm of trunk, arms, legs
Tinea manuum ringworm of hand
Tinea cruris ringworm of groin "jock itch"
Tinea pedis ringworm of foot "athlete's foot
Tinea unguium infection of nails
Ectothrix infection of hair shaft surface mycelium and spores on hair shaft
Endothrix infection of hair shaft interior mycelium and spores in hair shaft
C. Subcutaneous mycoses- infections involve the dermis, subcutaneous tissues, muscle, and fascia. These infections are chronic and are initiated by trauma to the skin. These infections are difficult to treat and may require surgical intervention.
Disease Etiological agent Symptoms ID of organism
Sporotrichosis Sporothrix schenckii
  1. yeast
  2. mold
Nodules and ulcers along lymphatics and at site of inoculation Yeast in tissue; mold at rm temp with "rosette pattern"
Chromoblastomycosis Fonsecaea pedrosoi or compacta, Wangiella dermatitidis warty nodules that progress to "cauliflower-like" appearance a inoculation site. copper-colored spherical yeasts called "Medlar bodies" in tissue
Mycetoma Pseudallescheria boydii, Madurella grisea or mycetomatis draining sinus tracts at site of inoculation white, brown, yellow or black granules in exudate that are fungal colonies
D. Systemic mycoses- infections that originate primarily in the lungs and may spread to many organ systems. These organisms are inherently virulent. All but Cryptococcus are dimorphic fungi.

Histoplasma capsulatum- Ohio and Mississippi river valleys, Yeast cells in tissue, Tuberculate macroconidia in mycelial phase.

Blastomyces dermatitidis- Ohio and Mississippi river valleys, Broad Base Budding yeast in tissue, Mycelia= microconidia

Coccidioides immitis- Southwestern US. Spherule in tissue, barrel-shaped Arthroconidia in mycelia phase.

Cryptococcus neoformans- Only yeast phase but unusual in that the cells are encapsulated as demonstrated by an India Ink stain.

E. Opportunistic mycoses- infections of patients with immune deficiencies who would otherwise not be infected. Ex. AIDS, altered normal flora, diabetes mellitus, immunosuppressive therapy, malignancy.

Candidiasis- Candida albicans- Creamy growth on various body surfaces. ex. mouth, skin, vagina. Budding yeast. Form pseudohyphae in tissue. Germ tube when grown in serum.

Aspergillosis- Aspergillus niger.

Take Care, and Think Microbiologically!!!

Last revised 8/28/13 by Neal R. Chamberlain, Ph.D.