myco and virology

• Clinical Classification of Fungi:

  • Superficial (cutaneous) Mycoses
  • Subcutaneous Mycoses
  • Systemic Mycoses
  • Opportunistic Mycoses
• Superficial Mycoses:

  • Infects outermost layer of skin or hair
  • Usually caused by agents that are non-dermatophytes
  • Important organisms:
  • Malassezia furfur - yeast
  • Piedraia hortae
  • Hortaea werneckii
  • Trichosporon spp. - yeast
• Malassezia furfur:

  • Skin colonizer with pigmentations
  • Loves warm environment
  • Lipid-loving
  • Causes dandruff
  • Common sites: Face, Chest, Trunk, Abdomen
  • Prevalent during warm weather
  • Laboratory Diagnosis:
  • Appearance under KOH: "spaghetti and meatballs fungus", Budding yeasts
  • Wood lamp: (+) Yellow fluorescence (in a blue background)
• Piedraia hortae (Septate Dematiaceous):

  • Causative agent of "black piedra"
  • Scalp hair infection with dark brown to black nodules containing ascospores
  • Differentiating the ascospores might crush the nodules
• Hortaea werneckii:

  • "Tinea nigra"
  • Brown to black non-scaly macules on palms and soles
  • Sometimes misdiagnosed as malignant melanoma
  • Non-inflammatory
  • Body yeast
  • Laboratory Diagnosis: Skin scrapings, 10-20% KOH, Hyphal elements with budding cells
• Trichosporon spp.:

  • Medically significant
  • Found in animals and in the soil
  • "white piedra" occurs in hair shaft, looks like dandruff
  • Opportunistic systemic pathogens
  • Associated with immunocompromised diseases
  • Normal biota of the skin
  • Species:
  • Trichosporon beigelii - human pathogen
  • T. asahii - fatal disease in immunocompromised hosts
  • T. mucoides - systemic disease (meningitis)
• Dermatophytes (Cutaneous Mycoses):

  • Utilizes keratin as a source of nitrogen
  • "keratinophilic" - hair, skin, and nails (dermatomycoses)
  • Important genera:
  • Trichophyton - hair, skin, nails
  • Microsporum - hair and skin
  • Epidermophyton - skin and nails
• Trichophyton:

  • Most common cause of infection
  • Causative agents of various types of ringworm
  • Anthropophilic
  • Laboratory Diagnosis: Direct Detection Methods with stains like Calcofluor white or potassium hydroxide
• Microsporum spp.:

  • Macroconidia: Echinulate spindle-shaped, thick-walled with four or more septa
  • Microconidia: Club-shaped, borne on hyphae
  • Colony varies in color (whitish to cinnamon brown)
• Most common cause of ringworm in dogs
• Test:

  • (+) Wood lamp
  • Calcofluor white or potassium hydroxide
• Macroconidia:

  • Tapering spiny distal ends (pointed or pointy)
• Colony:

  • Lemon-yellow or yellow-orange fringe
• M. gypseum:

  • Infection in hair & skin
  • Free living in the soil (geophilic)
  • Fusiform, thick-walled conidia
  • Spindle-shaped but not as pointed as distal ends of M. canis
  • Colony:
  • Powdery surface
  • Buff or cinnamon color
  • Undersurface is brownish
• Epidermophyton spp. Epidermophyton floccosum (common):

  • Common cause of tinea cruris and tinea pedis
  • Susceptible to cold
  • Slow grower
  • Microscopic appearance:
  • Thin-walled macroconidia
  • Multiseptate
  • Rounded tip
  • Colony:
  • Olive green to khaki
  • Dull orange-brown periphery
• Subcutaneous Mycoses:

  • Traumatic implantation of foreign objects leading to fungus entry
  • Agents are commonly found in soil or decaying vegetation
  • Infects muscle, connective tissue, etc.
  • Infection is seen where the trauma was
• Chromoblastomycosis:

  • Chronic fungal infection
  • Acquired through traumatic inoculation of organism
  • Papule found at site of trauma
  • Presence of Sclerotic Bodies:
  • Copper-colored, septate cells
  • Divide by binary fission
  • Resemble "copper pennies"
  • Agents: Cladophialophora carrionii, Fonsecaea pedrosoi, Phialophora verrucosa
• Laboratory Diagnosis:

  • Sample: Scrapings from crusted lesion
  • Test(s):
  • 10% Potassium Hydroxide (KOH): "muriform cells" - aggregation of dark brown cells
  • Molecular Method: MALDI-TOF MS
  • Cultivation:
  • Darkly pigmented colonies
  • Gray to olive black
  • Velvety or seudelike
• Phialophora verrucosa:

  • Microscopic appearance:
  • Phaeoid, flask-shaped phialides
  • Well-developed collarette
  • One-celled conidia oval
• Cladophialophora carrionii:

  • Microscopic appearance:
  • Sporulation with long chains of elliptical conidia
  • Erect conidiophores
  • Fusiform, conidia
  • Note: These fungi tend to be fragile
• Fonsecaea pedrosoi:

  • Microscopic appearance:
  • Sympodial arrangement of conidiophores
  • Primary conidia giving rise to secondary conidia
  • Some conidia may appear similar to other spp. of fungi
• Phaeohyphomycosis:

  • Infection in respiratory tract
  • Caused by darkly pigmented fungi
  • Distinguishable by phaeoid fungi
  • Agents: Alternaria spp., Bipolaris spp., Cladophialophora spp., Curvularia spp., Exophiala spp.
• Laboratory Diagnosis:

  • Direct microscopic examination
  • Histopathologic examination
  • Stains:
  • Fontana-Masson: detects melanization
  • 10% Silver Nitrate
  • Ammonium Hydroxide (stains fungal elements brown-black in red background)
• Alternaria spp.:

  • Chain of large brown conidia
  • "Drumstick" appearance
• Bipolaris spp.:

  • Septate hyphae
  • Geniculate Conidiophores - bent where conidia are attached
  • Conidia are oblong to fusoid
  • (+) Germ Tube: formed at both ends 25 o C at 24hrs
• Cladophialophora spp.:

  • Septate hyphae
  • Conidiophores are long and branched chains
  • Conidia:
  • Single-celled
  • Attachment scars
  • Wet Mount:
  • Shield Cells
  • Easily dislodged
  • Chains of conidia not seen
• Curvularia spp.:

  • Hyaline septate
  • Conidiophores are geniculate
  • Conidia:
  • Curved
  • Sympodial
  • Golden-brown
  • Central swollen cell (swollen cell at the center)
• Exophiala spp.:

  • Yeastlike cells
  • Produced by annellides
  • Conidiophores are cylindrical with tapered tip
  • Conidia:
  • Clusters
  • Round to oval
  • Note: It has basipetal succession
• Eumycotic Mycetomas:

  • Chronic infection that arises at site of inoculation
  • Characterized by swelling and exudate
  • Causes mycetomas
  • Can be caused by bacteria or fungi
  • Occur in tropical or subtropical areas
• Laboratory Diagnosis:

  • Molecular Method: Amplification test for fungal DNA in sterile body fluids
  • MALDI-TOF MS
  • Stain:
  • Hematoxylin-eosin
  • Methenamine Silver - appear black
  • Fontana-Masson - pigmented hyphae
• Scedosporium boydii (Anamorph) Pseudoallescheria boydii (Teleomorph):

  • Microscopic appearance:
  • Produces single oval conidia
  • Culture:
  • Rapid grower
  • White-dark gray colonies on Potato dextrose agar
  • Granules: White mycetoma
• Acremonium spp.:

  • Prev. Fusarium falciforme
  • Microscopic appearance:
  • Unbranched, multiseptated conidiophore
  • Clusters of single-two celled conidia
  • Conidia at tip of conidiophore
  • Granules: White mycetoma
• Madurella spp.:

  • Septate hyphae
  • Most cases of mycetoma
  • Microscopic appearance:
  • Long tapering phialides
  • Collarettes and sclerotia
  • Granules: Black mycetoma
• Sporothrix schenckii Species Complex:

  • Commonly manifest as lymphocutaneous sporotrichosis
  • Recovered from soil and decaying vegetation
  • Most cases are associated with gardening
  • "Rose Handler's Disease"
• Laboratory Diagnosis:

  • Direct Examination:
  • Small, cigar-shaped yeasts
  • Microscopic Examination:
  • Rosette pattern conidia
  • Dimorphic, examined at 22 o C - 37 o C