4. HDS Multisystem > Mycoses > Flashcards

Mycoses Flashcards

(38 cards)

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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
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2
Q

Superficial Mycoses

Overview

A

Infection of the stratum corneum

  • Etiologies:
    • Malassezia furfur and globosa
      • Lipophilic yeast
  • Disease:
    • Pityriasis versicolor (“Tinea versicolor”)
    • Fungemia with lipid infusions
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3
Q

Malassezia

Morphology

A

Clusters of thick-walled yeast cells mixed with hyphae

“Spaghetti and Meat Balls”

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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
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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
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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
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7
Q

Pityriasis Versicolor

Treatment

A

Topical azoles

Anti-fungal shampoos (selenium sulfide)

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8
Q

Cutaneous Mycoses

Overview

A

“Dermatophytosis”

  • Caused by Dermatophytes
  • Comprised of filamentous fungal species from three genera:
    • Trichophyton
    • Epidermophyton
    • Microsporum
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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
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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
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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
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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
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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
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14
Q

Cutaneous Mycoses

Sites of Infection

A
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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
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16
Q

Tinea Pedis

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A

Feet

Causes fissures between toes and erythematous, scaly, pruritic rash along lateral and plantar surfaces of feet

17
Q

Tinea Corporis

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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

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A

Ringworm of the groin; “jock itch”

Pruritic, erythematous rash with scaly border in the groin area

19
Q

Tinea Unguium

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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

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A

Ringworm of the beard

21
Q

Cutaneous Mycoses

Laboratory Diagnosis

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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

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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

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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

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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
25
Sporotrichosis Epidemiology
**"Rose Pickers Disease"** * Warmer climates including North and South America * Outbreaks of infection related to **forest work, mining, and gardening** have occurred * Classic infection is associated with traumatic inoculation of soil or vegetable or organic matter contaminated with the fungus
26
Sporotrichosis Clinical Symptoms
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
27
Sporotrichosis Laboratory Diagnosis
Definitive diagnosis depends on culture of the infected pus or tissue ## Footnote **At 25°C ⇒ hyphal form grows** **At 35°C ⇒ yeast form grows**
28
Sporotrichosis Treatment
Low-cost treatment is oral saturated potassium iodide daily for 3-4 weeks Itraconazole better
29
Opportunistic Mycoses
* **Primary location of infection includes oral, vaginal, urinary tract, and intestinal** * Most commonly caused by **Candida albicans** * Typically part of normal flora
30
Candidiasis Overview
* 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
Candida Morphology
* **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**
32
Candida Epidemiology & Transmission
* **Normal flora of oral cavity, genitalia, GI tract, or skin of most ppl** * Causes 80% of nosocomial fungal infections / 30% of deaths from nosocomial infections * Predominant source of infection is the patient ⇒ **endogenous infection**
33
Candidiasis Risk Factors
Predisposing host factors cause C. albicans to change from commensal to pathogen: * _For mucosal infections:_ * **Age (very young & very old)** * **Broad- spectrum abx use** * **DM** * **HIV** * **Immunosuppression** * _For vaginal infections:_ * **Oral contraceptives**
34
Candidiasis Pathogenesis
* **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
35
Mucocutaneous Candidiasis
* **Thrush** * Think, white, adherent growth on the MM of mouth and throat * **Vulvovaginal yeast infections** * Painful inflammatory condition of the female genital region * Causes ulceration and whitish discharge * **Cutaneous candidiasis** * Occurs in chronically moist areas of skin and burn pts
36
Candidiasis Clinical Symptoms
* **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
Candidiasis Laboratory Diagnosis
* 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
38
Candidiasis Treatment
* First eliminate any predisposing factors * Skin and mucosal infections * Treated with topical creams, lotions, ointments, and suppositories containing azole antifungal agents * Recurring or chronic mucosal infections * May require oral antifungals
4. HDS Multisystem
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