MYCOLOGY

• Serious Fungal Infections


  The size of the problem

  
• Opportunistic fungal diseases


  • Aspergillosi
  • Cryptococcal meningitis
  • Pneumocystis

  
• Tuberculosis And TB-like Fungal Diseases


  Chronic pulmonary aspergillosis cases after TB
• Types of mycoses


  • Superficial
  • Cutaneous
  • Subcutaneous
  • Systemic
  • Opportunistic

  
• Mycology


  The study of fungi

  
• Fungi


  • Eukaryotic
  • Have ergosterols in their membranes
  • Have a rigid cell wall made of chitin
  • Lack chlorophyll
  • Typically not motile, although a few (e.g. Chytrids) have a motile phase
  • Typically reproduce asexually and/or sexually by producing spores

  
• Moulds (Molds)


  Multicellular - form branching filaments called hyphae<|>A mass of hyphae collectively make up the mycelium
• Dimorphic fungi


  Some fungi exist in both yeast and mycelial forms<|>Yeast form: a parasitic or pathogenic form, usually seen in tissue of patients, can be cultured at 37 ℃<|>Mycelial form: a saprophytic form, existing in nature, can be cultured at 25 ℃

  
• Fungal Pathogenicity (virulence factors)

  Ability to adhere to host cells<|>Capsules allowing them to resist phagocytosis<|>Ability to damage host by secreting enzymes such as keratinase, elastase, collagenase<|>Ability to secrete mycotoxins<|>Exhibiting thermal dimorphism

  
• Differences between fungi and bacteria

  • Nucleus: Eukaryotic (fungi) vs Prokaryotic (bacteria)
  • Cytoplasm: Mitochondria, Endoplasmic reticulum present (fungi) vs absent (bacteria)
  • Cell membrane: Sterols present (fungi) vs absent except mycoplasma (bacteria)
  • Cell wall content: Chitin (fungi) vs Peptidoglycan (bacteria)
  • Spore: for reproduction (fungi) vs for survival (bacteria)
  • Thermal dimorphism: Yes (some fungi) vs No (bacteria)
  • Metabolism: Many Obligate anaerobes (fungi) vs No Obligate anaerobes (bacteria)

  
• Dermatophytes


  Fungi known as dermatophytes<|>Keratinophilic - "keratin loving"<|>Produce extracellular enzymes (keratinases) which are capable of hydrolyzing keratin<|>Classified into 3 genera: Microsporum, Trichophyton, Epidermophyton
• Dermatophyte ecology


  • Anthropophilic - Associated with humans only
  • Zoophilic - Associated with animals
  • Geophilic - Found in the soil and transmitted to man by direct exposure
• Tinea


  Produce ring-like lesions
• Clinical forms of tinea

  • Tinea capitis - Ringworm of the scalp, eyebrows and eyelashes
  • Tinea barbae - Ringworm of the beard
  • Tinea corporis - Classic "ringworm" on trunk, extremities, face
  • Tinea manuum - Ringworm of the palms and interdigits
  • Tinea ungium (onychomycosis) - Fungal nail infection
  • Tinea nigra - Caused by Exophiala werneckii and Cladosporium castellani
  • Tinea pedis (Athlete's Foot) - Fungal infection of the feet
  • Tinea cruris (Jock itch) - Fungal infection of the groin
• Tinea versicolor


  Fungal infection of the epidermidis that manifests as hypopigmented or hyperpigmented skin patches<|>Caused by Malassezia globosa or Malassezia furfur

  
• Black piedra


  Fungal infection of the hair shaft caused by Piedra hortae, forming hard black nodules on the hair shafts
• White piedra


  Fungal infection (Trichosporum beigelii) of the hair shaft, infected hairs develop soft greyish-white nodules along the shaft
• Laboratory diagnosis of fungal diseases

  • Direct microscopic examination
  • Culture of the organism
  • Histology/cytology
  • DNA probe tests
  • Serologic tests

  
• Microscopy techniques


  • Wet mount
  • 10-20% KOH mount
  • Lactophenol cotton blue stains
  • India Ink
  • Gram stain
• Culture


  Media SDA (Saboraud dextrose agar)<|>Moulds identified by macro and microscopic morphology

  
• Extensive advances in technology offer a vast identification of fungal species remains challenging in developing countries
• Emerging diagnostic technologies


  • Point-of-care lateral flow assay tests
  • Real-time PCR
  • Combination of real-time PCR and serological assays
  • Next-generation sequencing
  • CRISPR-based diagnostic tools
• Treatment


  • Topical - Nonspecific (Whitfield's ointment), Specific (Azole derivatives)
  • Oral antifungals - Griseofulvin, terbinafine, itraconazole
• Prevention


  Control depends on cleanliness, sterilization of instruments, effective treatment of cases and reduced contact with infectious materials
• Subcutaneous mycoses


  Chronic infections of the skin and subcutaneous tissue following traumatic implantation of the causative agent
• Mycetoma


  A mycotic infection characterized by draining sinuses and granules, resulting from traumatic implantation of the causative agent
• Mycetoma


  • Usually involves the cutaneous and subcutaneous tissue, can spread to the bone
  • Not contagious
• Aetiological agents of mycetoma

  • Madurella
  • Acremonium
  • Pseudallescheria
  • Exophiala
  • Leptosphaeria
  • Curvularia
  • Fusarium
• Eumycetoma


  Mycetoma caused by fungi, characterized by black or grey grains
• Actinomycetoma


  Mycetoma caused by filamentous bacteria, characterized by yellow to yellow-brown, white, pinkish-red, or white grains
• Causative agents of actinomycetoma

  • Streptomyces somaliensis
  • Actinomadura madurae
  • Actinomadura pelletieri
  • Nocardia brasiliensis
  • N. asteroides, N. caviae, N.coeliaca
• Laboratory diagnosis of mycetoma

  1. Obtain tissue biopsy or pus aspirate containing granules

  2. Examine pus with 10% KOH and Parker ink or calcofluor white

  3. Stain tissue sections with H&E, PAS digest, and Grocott's methenamine silver

  4. Culture on primary isolation media
• Treatment duration for mycetoma is long
• Phaeohyphomycosis


  Mycotic infection caused by dematiaceous (brown-pigmented) fungi where the tissue morphology is mycelial
• Causative agents of phaeohyphomycosis

  • Phialophora
  • Bipolaris
  • Exserohilum
  • Exophiala
  • Cladophialophora
  • Verruconis
  • Aureobasidium
  • Cladosporium
  • Curvularia
  • Alternaria
• Phaeohyphomycosis


  • Clinical forms range from localized superficial infections to subcutaneous cysts to deep infections in immunosuppressed patients
  • Current antifungal agents: posaconazole and voriconazole
• Subcutaneous phaeohyphomycosis


  Subcutaneous infections after traumatic implantation of fungal elements, commonly caused by Exophiala jeanselmei and Wangiella dermatitidis
• Paranasal sinus phaeohyphomycosis


  Sinusitis caused by dematiaceous fungi, especially in patients with allergic rhinitis, nasal polyps, and immunosuppression
• Cerebral phaeohyphomycosis


  Rare infection, mostly in immunosuppressed patients, caused by neurotropic fungi like Cladophialophora bantiana
• Laboratory diagnosis of phaeohyphomycosis

  1. Obtain skin scrapings, tissue biopsies, aspirates, cerebrospinal fluid

  2. Examine specimens with 10% KOH and Parker ink or calcofluor white, and stain tissue sections with H&E, PAS digest, and GMS

  3. Culture on primary isolation media

  4. Identify based on culture characteristics and microscopic morphology