Download Superficial Infections

Cutaneous Fungal Infections
Superficial Skin Infection
Name
Diagnosis/Labs
Tinea versicolor
Caused by Malassezia species
Labs/Microscopy
- KOH mount for definitive diagnosis
(degrades everything but chitin)
- Enhanced with Calcofluor white die which
binds to cellulose/chitin
Pseudohyphae AND
yeast
- Lesions fluoresce yellow-green in Wood’s
light
- See mixture of pseudohyphae and clusters of
yeast
Culture
- Grows in Sabouraud agar only if containing
lipid
Dermatophytosis (Ringworm) – Keratinized tissues
1. Trichophyton – micro/macro conidium
2. Microsporum – micro/macro conidium
3. Epidermophyton – Thallic - soliatary
- Distinguished by details of spores produced in vitro. Spores not
produced in vivo. Telomorphs are possible, too.
Labs/Microscopy
- KOH mount – removes everything except chitin in cell walls
See branching hyphae with septa +- arthrospores
- Sabouraud culture at 30°C 2-4 weeks is ESSENTIAL since many
species
- Use cyclohexamide + antibacterial in culture
Tinea pedis
- Trichophyton rubum
(Athlete’s Foot)
- Trichophyton mentagrophytes
variant interdigitale
Tinea cruris
(Jock itch)
Tinea corporis
- Trichophyton rubum
- Epidermophyton floccosum
KOH mount: see branching hyphae with septa
Caused by several species that are
- Zoophilic (ex. Microsporium canis)
- Geophilic – requires high dose/immunocomp.
- Anthropophilic – less common, less inflamm.
©2009 Mark Tuttle
Symptoms
- Causes discolored skin without
inflammation
- Overgrowth of yeast in lesions
Complications
 Premature infants who are given
intralipid nutrition by infected
Broviac catheters.
Get generalized infection with
septicemia, pneumonia
 AIDS patients get severe
folliculitis and seborrheic
dermatitis, C5a produces
inflammation
Pathogenesis
- Lipophillic yeast. Will not grow
in absence of lipid
- Normal flora of skin, especially
oily skin
- Grows ONLY in stratum corneum
- Not a severe disease
- Outside: Ring of inflammation
- Middle: mycelium
- Can scratch and re-inoculate the
middle
- True pathogens. Not normal
- Perhaps nitrite as
flora.
treatment since
- Anthropophilic species usually
nitrosylated
not as severe as zoophilic or
keratin is toxic to
geophilic
fungi
Virulence factors
- Proteinases
Keratinase, elastase, collagenase
- Sulfite
Reduces disulfide bonds in
keratin
- Anthropophillic
Arthrospores
Branching, septate
hyphe
- Most often between 4th and 5th
toe
- Can be symptom-free carrier
- Picked up from infected skin
scales containing arthrospores
- Ringworm on body, arms, trunk
- Incubation period is up to 3
weeks
- Especially susceptible with skin
abrasion and perpetual
dampness (Vietnam)
- Poor invasiveness since no
growth at 37C and unable to
access Fe in deep tissues
- T-cell mediated immunity is
important (AIDS get severe)
- Natural antifungal skin fatty acid
Treatment
- Keratinolytic
(propylene glycol)
- Selenium sulfide
(dandruff
shampoo)
- Azole
Used for severe
recurrent infections
of unknown
etiology
-
Dermatophytosis (Ringworm) – Keratinized tissues (Continued)
Name
Diagnosis/Labs
Tinea capitis
Ectothrix: Grows within/outside hair
- Microsporum cani/audouinii
- Most common before puberty
Onychomycosis
Symptoms/ Pathogenesis
- Hair becomes infected and breaks off leaving
patches of baldness
Favus – comes out the end of the hair follicle
- Scarring disease of hair follicle. T. schoenleinii
Endothrix: Grows within hair only
Kerion
- Trichophyton tonsurans (monk)
- Boggy tumor associated with inflammatory response
- Continues after puberty
to infected hair follicles
Id reactions
Labs
- Inflammation and blistering at distal sites where no
- Fluoresce in Wood’s Light
infection is present
Nail infection, often due to dermatophytes. Hardest to treat and may be mixed with bacteria
Mycotic Keratitis
Fungal infection of the eye.
©2009 Mark Tuttle
Treatment
Limited areas: Topical agents
- Tinactin, clotrimazole
- Whitfield ointment
(Benzoic + salicylic acids)
Large areas: Oral therapy
- Azoles, Griseofulvin, allylamines
Epidemics
- X-irradiation, griseofulvin, azole
antifungal