Lecture 47: Fungi SBM

Question 1

White Piedra

Answer 1

• superficial infection caused by Trichosporon
  
  • part of spore-forming Anthrocondia
  • can infect cutaneous tissue
  • can disseminate systemically
• Sx of white piedra
  
  • asx growth on outside of hair shaft, white, green, or yellowish soft nodules
• Rx: shaving and antifungals
  
  • amphotericin B
  • all azoles

Question 2

Black Piedra

Answer 2

• caused by ascomycete genus Piedraia spp
• Asx but visible colonization of shaft of scalp hair
• disorder restricted to tropics
• Rx: difficult, azoles w limited success

Question 3

Tinea nigra

Answer 3

• don’t confuse w black piedra on hair
• Tinea nigra caused by Hortae werneckii (Exophiala werneckii)
• brown-black lesion on hands and feet; pigmentation more intense at borders; no invasion of living tissue only outer dead layers of skin
• colonies are smooth w oily glistening, olive-black colour

Question 4

Pityriasis versicolor aka Tinea versicolour

Answer 4

• Pityriasis versicolor caused by Malassezia furfur
• infects all layers of stratum corneum
• Sx: usually superficial, chronic, and asx
  
  • macular rash or fine scaling of upper trunk and shoulders
• Dx: skin scraping and microscopy
  
  • M. furfur morphology of both filaments and yeast (spaghetti and meatballs)
• Rx: antifungals

Question 5

Other infections w Malassezia spp

Answer 5

• opportunistic systemic infections via central venos catheters
• may cause seborheic dermatitis & dandruff
• Dx: yeast isoltion on lipid-containing media

Question 6

Cutaneous mycoses: Dermatophytes

Answer 6

• commonly called ring worm and jock itch
• fungi using keratin as nutrient source -> colonize keratized stratum corneum only
• Sx: typical skin lesion
  
  • annular. scaly pathc w raised margin
  • infection of hair causes hair loss and dry, scaly patch of skin
  • nails become yellow, thickened, and cracked
• Predisposing conditions to chronic infection
  
  • nl person w minor immunological blind spots
  • old age
  • collagen vascular disease
  • diabetes
  • hematological malignancy
• 3 sources of infection: humans, zoonotic, soil

Question 7

Microsporium

Answer 7

• attack skin and hair but NOT NAILS
• microsporum form both macroconidia & microconidia

Question 8

Epidermophyton spp

Answer 8

• Epidermophyton attacks skin & nails but does NOT invade hair
• E. floccosum is the onl pathogenic spp
  
  • macroconidia w smooth walls
  • born-singly or in banana-like clusters
  • microconidia abset

Question 9

Trichophyton spp

Answer 9

• Trichophyton attack skin, hair, and nails; noted for lifelong nail infection.
• microconidia > macroconidia
• T. mentagrophytes, rubrum, tonsurans (major cause of ringworm in skin)

Question 10

Clinical forms of dermatophyte infection

Answer 10

• infections caused by dermatophytes clinically classified on basis of location of lesions on body

Question 11

Tinea corporis

Answer 11

• ringworm involving trunk, shoulder, axilla, chest, and back
• lesions are well marginated w raised erythematous, vesicular bordrs
• most serious chronic infection due to T. rubrum

Question 12

Tinea cruris aka Jock itch

Answer 12

• frequently caused in adults by T. rubrum & E. floccosum
• sx: lesions are erythematous, scaly, raised inflamed borders, often w vesicles
  
  • itching/burning

Question 13

Tinea capitis

Answer 13

• Ectothrix invasion when fungus forms sheath of hyphae and arthroconidia around shafts of hair.
  
  • Microsproum spp. common causes
• Endothrix invasion when hyphae invade hair follicle and shaft and form many spores w/in hair shaft
  
  • infected grayish-white hairs break off easily at scalp giving black dot apperance.
  • Trichophyton tonsurans common cause

Question 14

Tinea pedis

Answer 14

• sx: scaling, fissuring, erythema, itching, and burning
• acute condition characterized by vesicles, inflammation, and pustules (sterile)
• T. mentagrophytes, T. rubrum, E. floccosum common causes

Question 15

Tinea barbae

Answer 15

• zoonotic Triphyton spp. common causes
  
  • T. verrucosum: cattle
  • T. mentagrophytes: mice & rodents

Question 16

Tine unguium

Answer 16

Tinea unguium

• invasion of nail plate
• T. rubrum, T. mentagrophytes, E. floccosum common causes

Question 17

Rx of dermatophyte infections

Answer 17

• orally active triazoles
• allylamines (terbinafine)
• griseofulvin & ketoconazole
• topical antifungals thiocarbonates (tolfnaftate) and imidazoles
• systemic antifungal require long periods of rx (3 mo); toxic for liver; newer antifungals safer
  
  • itraconazole
  • terbinafine

Question 18

Candidiasis of skin

Answer 18

• diaper rash
• bw folds of skin in obese Pt
• lesions appear as erythematous papules
• Dx: Gram stain
  
  • pseudohyphae
  • Germ tube positive
• Rx: reduce moisture and chronic trauma
  
  • Nystatin or clotrimazole

Question 19

Fungal eye infection

Answer 19

• Fusarium commonly infects due to its pointed curved shape
• also various other fungal causes

Question 20

External otitis

Answer 20

• Asperigillus spp. most common cause
• Fusarium spp. also caue

Question 21

Hyalohyphomycosis vs Phaeohyphomycosis

Answer 21

• Hyalohyphomycosis: non-black modl fungal infections
• Phaeohyphomycosis: black mold fungal infections
  
  • Alternaria spp.
  • chromoblastomycosis aka verrucuos dermatitis
    
    • soil fungi of genera Phialophora and Cladosporium
    • traumatic inoculation -> wart-like nodules -> crusty abscesses -> infection remains localised -> slow painful infections

Question 22

Sporotrichosis

Answer 22

• Rose gardener’s disease (subcutaneous disease) or alcohol-rose gardener’s disease (pulmonary)
• caused by sporothrix schenckii -> cigar-shaped yeast
• infection by splinters, thorns and cuts of skin
• flower-like colonies
• Rx: oral KI in milk or itraconazole

Question 23

Eumycetoma - Madura foot

Answer 23

• unsual infection associated w trauma to feet, lower extremities and hands
• innoculation causes local swelling w suppuration and bascess formation -> granulomas and draininig sinuses
• Pseudoallescheria boydii most common
• Rx:
  
  • surgical debridement
  • nystatin (topical) or miconazole (systemic)

Question 24

Dx of superficial fungal infection

Answer 24

• microscopy: PAS, silver stain, Sabouraud’s agar culture
• Wood’s UV light: T. versicolor or T. capitis (microsporum canis and microsporum audouinii)

Question 25

Mycobacterial marinum infections of skin

Answer 25

• M. marinum: produce yellow pigment
  
  • requires 28 to 30 C for optimal growth
  • persons working in sea, boats, aquarium, ponds, marshes
  • requires traumatic innoculation

Question 26

M ulcerans infection of skin

Answer 26

• M. ulcerans:

Buruli ulcer
slow growing non-photochromogen

requires 28 to 30 C for optimal growth

Question 27

M. chelonae

Answer 27

M. chelonae

• causes soft tissue abscesses & chronic cutaneous lesions
• Rx: surgical excision plus cefoxitin and amikacin