Cutaneous Fungal Infections

Question 1

Characteristics of Fungi

Answer 1

Yeast, Molds, Rusts, and Mushrooms
Eukaryotic, aerobes or facultative anaerobes
Typically non-motile
Unique rigid cell walls (e.g.,glucan, chitin) and ergosterol in cell membrane are targets for anti-fungal antibiotics
Heterotrophic and absorptive nutrition
Pathogenic fungi grow best at 25-30ºC and at acid pH

Question 2

Morphology of Molds

Answer 2

Hyphae (the mold form of growth)
Tubular, branching filaments (2–10 μm in width) of fungal cells, with or without cross walls (septate or non-septate hyphae)
mycelium- Mass or mat of hyphae, mold colony

Spore (reproductive structure)
Sexually or asexually (conidia) generated structures resist adverse conditions and promote dispersion. Spores disperse, germinate and grow by apical elongation into hyphae.

Question 3

Filamentous Molds

Answer 3

Vegetative hyphae penetrate the substrate for absorptive nutrition

Fungal mycelium: loose network of hyphae

Aerial hyphae differentiate into spore-producing or conidia- producing structures.

Question 4

Morphology of Yeast

Answer 4

Unicellular, spherical to ellipsoid (3–15 μm) fungal cells that usually reproduce by budding.

Elongated chain of budding yeast may form (pseudohyphae)
If in nutritional environment, they will send out a germ tube so that the bud will elongate and mimic a hyphal structure and create pseudohyphae

Question 5

Types of Fungal Disease

Answer 5

1. Allergic
2. Toxic

3. Infectious:
Superficial - Noninvasive, noninflammatory infection of hair, outermost dead skin; cosmetic symptoms only
Cutaneous  
Subcutaneous 
Systemic (true fungal pathogens)
Opportunistic

Question 6

Fungal Virulence vs. Host Defenses

Answer 6

Most fungi are poorly virulent and noninvasive in immunocompetent people

Phagocytes (neutrophils) readily ingest and kill most fungi. Strong cell-mediated immunity (Th1 and Th17) is induced by fungal agents of cutaneous infection and systemic infection.

Neutrophil and CMI deficiency predisposes to systemic fungal infection.

Fungal pathogens lack toxins but can cause tissue necrosis (via infarction) and inflammatory injury (DTH reactions) by absorbing nutrients via digestion of tissues; hyphal elements will penetration blood vessels and damage them and get local necrosis or ischemia; also local inflammatory processes in sites of infection

Question 7

Superficial Fungal Infections

Answer 7

Tinea Versicolor: chronic mild, usually noninflammatory infection of stratum corneum; hypo and hyperpigmented macules with scales; lesions fluoresce under UV light

Tinea Nigra: brown black non-scaly macules on palmar surface and soles

Black Piedra: infection of scalp hair shaft with black hard nodules

White Piedra: infection of external scalp hairshafts forming soft irregular whitish nodules on shaft

Mycotic Keratitis: trauma induced infection of cornea or ear

Question 8

Malassezia

Answer 8

Malassezia, a lipophilic yeast that may be normal flora, is associated with seborrheic dermatitis (dandruff)
Scraping of the skin and look for fungal morphology, put KOH on it and examine with light microscope; normal skin cells with lose the architecture with KOH, but the fungal walls resist KOH
Spaghetti and meatballs - causes tinea versicolor

Question 9

Cutaneous Fungal Infections: Dermatophyte Infections

Answer 9

Dermatophytes: fungal agents (in soil, on animals and humans) that degrade and grow on keratin

Dermatophytoses: fungal infections of the keratinized tissues (hair, skin, nails).
Contagious by direct contact
Restricted to outer layers due to temperature tolerance of fungi
Strong cell-mediated immune response explains the inflamed skin lesions of ringworm
etiologic agents: Trichophyton, Microsporum, Epidermophyton

Question 10

Dermaphyte Infections Association with Body Sites

Answer 10

Trichophyton species: infect hair, skin, or nails.

Epidermophyton species: infect the skin and nails but not hair.

Microsporum species: infect only hair and skin

Question 11

Tinea Pedis

Answer 11

Athlete’s foot
Common agents = T. rubrum, T. mentagrophytes, E. floccosum

Dry flaky and minimal inflammatory, but can become boggy and highly inflammatory = depends on amount of keratin present and environmental conditions; love highly keratinized areas that are moist and warm

Have in groin, armpits, feet, under breasts
Use of lotions and creams, sweat a lot = risk

Question 12

Tinea Unguium

Answer 12

Tinea unguium (onychomycosis)
Common agents= T rubrum, T mentagrophytes, E floccosum)

Nail becomes brittle, yellow
Any fungal infections, dermaphytes = scrap + KOH = see fungal structures because KOH won’t change them

Question 13

Tinea Capitis

Answer 13

Tinea capitis- ringworm of scalp and hair
A Wood’s lamp can be used diagnostically to detect fluorescence of some agents of tinea capitis.

See inflammation and hair loss
Can grow outside hair shaft or penetrate hair shaft
Cell mediated immune response = more inflammation
Kerion formation: high inflammation areas with hair loss; moist keratinized areas

Question 14

Agents of Tinea Capitis

Answer 14

T. mentagrophytes: fungal growth PENETRATES hairshaft = endothrix spores, non-florescent
“black dot”

M. canis: fungal growth forms sheath on OUTSIDE of hairshaft = ectothrix spores, fluorescent
animal acquired, nodular clusters of fungus
Used to cause epidemic tinea capitis

Question 15

Tinea Corporis

Answer 15

Tinea corporis (“ringworm”) caused by Trichophyton mentagrophytes contracted from a dog; hair areas

On hairless areas, common agents = T rubrum, E floccosum

Question 16

Tinea Cruris

Answer 16

Tinea cruris (jock itch)
Common agents = T rubrum, T mentagrophytes, E floccosum
KOH Prep

Question 17

Dx of Dermaphyte Infections

Answer 17

Direct microscopic exam for fungal morphologies in skin/hair/nail scrapings (KOH prep or fluorescent stains for chitinous cell walls).

Lab culture of dermatophyte from sample (dermatophyte test medium) and morphological identification.

Question 18

Therapy of Dermaphyte Infections

Answer 18

Topical anti-fungal agents, keratolytics
Systemic antifungals for nail infections
Good hygiene, keep areas dry

Question 19

Subcutaneous Fungal Infections

Answer 19

Acquired from soil or plant material by traumatic implantation in patients with mild immunosuppression
Spread along lymphatic channels in subcutaneous layer
Strong cell-mediated immune response plus suppuration
Example: sporotrichosis caused by Sporothrix schenckii

Question 20

S. schenckii

Answer 20

S. schenckii, a dimorphic fungus, appears as yeast in tissues (37ºC) and a mold at 20ºC.
Subcutaneous Infection
*Unicellular yeast form in the skin, or if culture it will grow as a mold in the lab = grows in two different forms in two different temperatures

Question 21

Chromomycosis and Actinomycetoma

Answer 21

Chromomycosis: traumatic implantation of dematiaceous (pigmented) soil fungi.
See in tropical areas with farming and people aren’t wearing shoes and get from soil
Verrucous / cauliflower lesions on skin
Soil fungi are pigmented (can be colored but usually dark)

Actinomycetoma is caused by implantation of filamentous soil bacteria, not fungi

Subcutaneous Infections

Question 22

Mycetoma and Phaeohyphomycosis

Answer 22

Mycetoma: can be pigmented with yellow or red and get granulomatous lesions (supportive) and will drain and have tracts; same kind of lesion can be caused by a bacteria, so differentiate in lab

Phaeohyphomycosis

Subcutaneous Infections

Question 23

Candida albicans

Answer 23

Candida albicans (also Candida tropicalis, Torulopsis glabrata)
Yeast in laboratory culture but forms pseudohyphae (germ tubes) when grown in serum or in tissues

Normal flora in humans (oropharynx, gastrointestinal tract, vagina). Most infections are of endogenous origin but may be contagious

Opportunistic: grows best in immunocompromised host (depressed cell-mediated immunity) or in host with altered normal bacterial flora

Predisposing factors: breaks in skin, low neutrophils, decreased lymphocyte function, corticosteroids, diabetes, antibiotic therapy, pregnancy, use of contraceptive pills

Cutaneous Fungal Infection:Non-dermatophyte agent

Question 24

Candida Infections (Candidiasis)

Answer 24

Mucocutaneous candidiasis:
Oral Thrush- common in elderly homes because immunosuppressed
Esophagitis 
Nonesophageal Mucous Membrane 
Gastrointestinal Candidiasis 
Vaginitis 

Cutaneous candidiasis:
Generalized cutaneous
Folliculitis
Balanitis
Onychomycosis (nail infection)
Paronchyia (candida of hands & fingers in "wet workers")
Diaper rash, Perianal

Question 25

Cutaneous Lesions Associated with Systemic Fungal Infections

Answer 25

Systemic Fungal Pathogens cause a primary self-resolving respiratory infection in immunocompetent patients but systemic agents disseminate to disease-specific target organs in immunocompromised patients

Infection occurs via inhalation of a large inoculum of spores generated by disturbance of soil with high filamentous mold growth due to enrichment with bird or bat droppings in chicken coops, bat caves, parks with pigeon populations, natural bird roost areas

Geographic localization of fungi: disease association with certain occupations and geographic areas
Diagnosis must be consistent with probable exposure

Strong cell-mediated immune response with granulomatous inflammatory response

Question 26

Cutaneous Lesions Associated with Systemic Fungal Infections: Histoplasmosis, Blastomycosis, and Paracoccidiomycosis

Answer 26

True fungal pathogens = all acquired from inhalation and can happen in perfectly healthy
Dissemination to the skin as a target organ occurs in:

Disseminated Histoplasmosis: mucocutaneous ulcers of the nose, mouth, tongue

Disseminated Blastomycosis: skin lesions on exposed surfaces; may evolve to ulcerated verrucous granulomas

Disseminated Paracoccidiomycosis: mucocutaneous lesions (often oral: granulomas with central caseation or microabscesses )

Question 27

Cutaneous Lesions Associated with Systemic Fungal Infections: Coccidioidomycosis

Answer 27

Pulmonary Coccidioidomycosis: 15% of patients develop hypersensitivity reactions, which present as a rash, erythema nodosum, or erythema multiforme.

Disseminated Coccidioidomycosis: extrapulmonary skin lesions occur after 1 year in

Question 28

Diagnosis and Lab ID of Systemic Fungal Pathogens

Answer 28

Dimorphism (temperature dependent):
True fungal pathogens grow as filamentous molds at room temperature but as unicellular yeasts in infected tissues at body temperature.

Mold & yeast form morphologies

Fungal-specific immune responses:
DTH skin test reactivity
Rising antibody levels
Presence of fungal antigen in tissues or blood

Question 29

Dimorphic Growth of Systemic Fungi

Answer 29

Systemic fungi are “dimorphic”, growing as yeast at 37ºC but growing as filamentous molds at room temperature

Blastomyces dermatitidis yeast cell undergo broad-base budding (37°C), but mold with microconidia at 20°C.

Question 30

Opportunistic Fungal Infections

Answer 30

Suppurative necrotic responses; immunocompromised patients are mostly at risk

Not geographically restricted; normal flora or ubiquitous in the environment.

Diseases and etiologic agents:
Candidiasis (C. albicans)
Aspergillosis (Aspergillus fumigatus, A. flavus, etc.)
Pseudallescheriasis (Pseudallescheria boydii)
Mucormycosis (Rhizopus, Absidia, Mucor species)
Pneumocystis pneumonia (Pneumocystis jirovecii)
Penicillosis (Penicillium marneffei = AIDS-defining disseminated infection, S.E. Asia)
Cryptococcal meningitis (Cryptococcus neoformans)