Mycoses Flashcards
1
Q
Fungal Infections (Mycoses)
Classification
A
Typically classified according to tissue level primarily infected:
-
Superficial (skin or mucosa)
- Mycoses caused by fungi that colonize the outer keratinized, non-living, layers of skin and hair
-
Cutaneous
- Mycoses are common
- Caused by dermatophytes
- Can invade the outermost layer of the epidermis, including the hair and nails
-
Subcutaneous
- Typically initiated by traumatic inoculation of the fungus through damage to the skin
- Can involve dermis, subQ, muscle, fascia, and in some instances lymphatic tissue
-
Mucosal (Opportunistic)
- Most typically vaginal and oropharyngeal
- Caused by candida species
- Opportunistic yeast that normally inhabits these sites
-
Systemic
- “True pathogens”
- Infect healthy hosts
- “Opportunists”
- Disease almost exclusively in immunocompromised
- “True pathogens”
2
Q
Superficial Mycoses
Overview
A
Infection of the stratum corneum
-
Etiologies:
-
Malassezia furfur and globosa
- Lipophilic yeast
-
Malassezia furfur and globosa
-
Disease:
- Pityriasis versicolor (“Tinea versicolor”)
- Fungemia with lipid infusions
3
Q
Malassezia
Morphology
A
Clusters of thick-walled yeast cells mixed with hyphae
“Spaghetti and Meat Balls”
4
Q
Malassezia
Epidemiology & Transmission
A
- Worldwide distribution particularly in tropical and subtropical regions
- Most common in young adults
- Spread by transfer of infected skin and person-to-person contact
5
Q
Pityriasis Versicolor
Clinical Symptoms
A
-
Hyper and hypopigmentation of upper torso and arms, that can be scaled
- Skin lesions fluoresce under a Wood (UV) lamp
- Can cause dandruff and seborrheic dermatitis
- Generates little or no host immune response
6
Q
Pityriasis Versicolor
Diagnosis
A
- Requires culture in the presence of lipids
- Visualization of fungus, “spaghetti and meat balls”, from epidermal sample treated with KOH
- Skin lesions fluoresce under a wood (UV) lamp
7
Q
Pityriasis Versicolor
Treatment
A
Topical azoles
Anti-fungal shampoos (selenium sulfide)
8
Q
Cutaneous Mycoses
Overview
A
“Dermatophytosis”
- Caused by Dermatophytes
- Comprised of filamentous fungal species from three genera:
- Trichophyton
- Epidermophyton
- Microsporum
9
Q
Dermatophytes
Morphology
A
- Hyaline septate hyphae, chains or arthroconidia, or dissociated chains of arthroconidia
- Classified by presence and characteristics of macroconidia and microconidia in culture:
- Epidermophyton ⇒ do not produce microconidia
- Trichophyton ⇒ produce many microconidia
- Microsporum ⇒ identified by its macroconidia
10
Q
Dermatophytes
Ecology
A
- Worldwide distribution
- Individual species w/ distinct geographical regions & ecological niches
- Are not members of the normal flora
- Ability to survive on wet surfaces, likely contributing to transmission
11
Q
Dermatophytes
Epidemiology & Transmission
A
- Transmission via transfer of arthroconidia or hyphae
- Need exposure & break in the skin
- Both sexes and all ages are susceptible to dermatophytosis
-
Some are more common in specific genders or age groups
- Tinea pedis has a preference for infecting males
- Tinea capitis is more common in prepubescent children
- Site of infection can be influenced by age of host
- Overall incidence higher in males than in females
- Ratios of 3:1 for tinea capitis and 6:1 for tinea pedis
- Worldwide, T. rubrum and T. mentagrophytes account for 80-90% of infections
12
Q
Cutaneous Mycoses
Pathogenesis
A
- Dermatophytes invade the skin, hair or nails
- Patterns of invation can be either:
- Ectotrix ⇒ remains confined to hair surface
- Endotrix ⇒ invades the hair shaft and internalizes into hair cell
- Favic ⇒ saucer-shaped crusted lesions or scutula
- Fungi are keratinophilic & keratinolytic
- Can breakdown keratin to gain entry to the uppermost layer of skin
- Secrete keratinase
- Typically invade only the upper outermost layer of the epidermis, the stratum corneum
- Penetration below the granular layer of the epidermis rare
13
Q
Cutaneous Mycoses
Clinical Symptoms
A
- Dermatophyte infections called “tineas”
- Subdivided according to site infected
- Clinical signs and symptoms vary according to the etiologic agents, host reaction, and site of infection
- Dermatophytes spread though stratum corneum, outward from point of infection, giving a characteristic ring shape ⇒ “ring worm”
- Viable fungi are at the perimeter of the ring
- Fungal invasion of the nails occurs through the lateral or superficial nail plates then spreads throughout the nail
- When hair shafts are invaded, organisms can be seen either within the shaft or surrounding it
- Rash is often erythematous
14
Q
Cutaneous Mycoses
Sites of Infection
A
15
Q
Tinea Capitis
A
Hair & Scalp
- Presents with well-demarcated scaly patches
- Hair shafts have broken off right above the skin
- Most commonly T. tonsurans (endothrix)
- Fluoresce green under wood’s (UV) lamp
16
Q
Tinea Pedis
A
Feet
Causes fissures between toes and erythematous, scaly, pruritic rash along lateral and plantar surfaces of feet
17
Q
Tinea Corporis
A
Ringworm of the body
- Well-demarcated, pruritic, scaly lesions
- Undergo central clearing as the lesion expands
- Often 1 or more small lesions are present
- More extensive involvement less likely
18
Q
Tinea Cruris
A
Ringworm of the groin; “jock itch”
Pruritic, erythematous rash with scaly border in the groin area
19
Q
Tinea Unguium
A
Ringworm of the nail, a.k.a. Onychomycosis
- Caused by a variety of dermatophytes
- Estimated to affect ~3% of the population in most temperate countries
- Mostly seen in adults
- More commonly affects toenails than fingernails
- Infection is usually chronic
- Nails become thickened, discolored, raised, friable, and deformed
-
T. rubrum is most common etiologic agent
- Can also be caused by candida
20
Q
Tinea Barbae
A
Ringworm of the beard
21
Q
Cutaneous Mycoses
Laboratory Diagnosis
A
- KOH treatment of skin/sample
- Microscopic observation of hyaline, septate, branching hyphae confirms dx of dermatophyte infection
- Culture is required to identify specific species
-
Macroconidia and microconidia can be observed after culture in mycosel or mycobiotic agar selective for dermatophytes
- Contains cycloheximide and chloramphenicol
22
Q
Cutaneous Mycoses
Treatment
A
For most localized non-hair and non-nail infections:
- Topical treatment with specific antifungal (azoles, allylamines) is usually sufficient
- Nail lacquers for onychomycosis can be used in mild cases
- Otherwise oral terbinafine
- Especially with any severe infection or in immunocompromised patients
- Successful therapy of nail infection may require many months
- Discontinuation of therapy before then may result in relapses
23
Q
Subcutaneous Mycoses
Overview
A
- Caused by fungi that normally reside in soil
- Typically initiated by traumatic inoculation of the fungus through damage to the skin
- Infections and can involve dermis, subcutaneous, muscle, fascia, and in some instances lymphatic tissue
- Can rarely become systemic
- Infection is chronic and hard to treat
- Sporotrichosis caused by Sporothrix schenckii is the most common infection
24
Q
Sporothrix schenckii
Morphology
A
-
Thermally dimorphic
- Ambient temperatures (25°C) grows as a mold w/ septate hyphae & conidia that contain melanin
- 37°C grows as small budding yeast
- Mycelial-form cultures grow rapidly
- Wrinkled membranous surface that gradually becomes tan, brown, or black
- Microscopically:
- Mold form consists of narrow, hyaline, septate hyphae
- Produce abundant oval conidia
26
Q
Sporotrichosis
Clinical Symptoms
A
Rose Pickers Disease
- Classically appears after local trauma to an extremity
- Nodule appears at site of initial infection
- Spreads through lymphatic system creating additional nodules
- Secondary lymphatic nodules appear ~ 2 weeks s/p appearance of the primary lesion ⇒ linear chain of painless subcutaneous nodules
- Extend proximally along the course of lymphatic drainage of the primary lesion
- Lesions may ulcerate
- Very occasionally disseminates
30
Q
Candidiasis
Overview
A
- Most important group of opportunistic fungal pathogens
- Candida albicans can cause two classes of disease
- Mucosal infections
- Systemic infections
- 90-100 % of mucosal infections are caused by C. Albicans
- Remainder by C. glabrata, C. parapsilosis, C. tropicalis, C. krusei
31
Q
Candida
Morphology
A
-
C. albicans is thermally dimorphic
- 25°C ⇒ budding yeast
- 37°C ⇒ hyphae (“germ tube”)
- All candida species exist as oval yeast-like forms that produce buds or blastoconidia
- Species of candida other than C. glabrata also produce pseudohyphae and true hyphae
34
Q
Candidiasis
Pathogenesis
A
-
Morphogenesis ⇒ important virulence factor
- Allows rapid multiplication and dissemination in host
- Yeast and hyphal forms of C. Albicans bind epithelial and endothelial cells via specific proteins
- Proteins recognize fibronectin and other host proteins
- Hyphae can invade host cells through the production of:
- Proteinases
- Phospholipases
- Lipases
- If tissue invasion continues unabated, a systemic infection can arise
36
Q
Candidiasis
Clinical Symptoms
A
-
Oropharyngeal (thrush) and vaginal infections
- Overgrowth of candida seen as a white “cottage cheese like” patches
-
Pseudomembranous type
- Has a raw bleeding surface when scraped
-
Erythematous type
- Recognized by flat red areas
- Leukoplakia ⇒ non-removable white layer covering epithelium tissue
-
Angular cheilitis ⇒ sore corners of the mouth
- Other areas of infection include the groin and breast-folds
- Onychomycosis was discussed earlier
37
Q
Candidiasis
Laboratory Diagnosis
A
- Microscopic examination of scrapings from lesions after treatment with KOH
- Reveals budding yeast and hyphal forms
- Visualization of characteristic budding yeasts and pseudohyphae is sufficient for diagnosis of candidiasis
- Specimens can be cultured on selective medium e.g. chromagar
-
Can distinguish species by colony color
- C. albicans ⇒ green
- C. tropicalis ⇒ blue
- C. krusei ⇒ pink
- Other species ⇒ white to mauve
- Sugar assimilation test strips can also provide candida species identification
- For suspected C. Albicans a “germ-tube” formation test can be performed
