Fungal Infections of Humans

• Classification of fungal diseases

  • Superficial mycoses
  • Cutaneous, hair, and nail mycoses (tinea or "ringworm" infections)
  • Subcutaneous mycoses
  • Systemic mycoses
• Superficial mycoses


  • Fungal infections of the outermost areas of the body (outer surfaces of hair shafts, the epidermis)
  • Most often diagnosed by clinical appearance

  
• Dermatophytosis (Tinea ["Ringworm"] Infections, Dermatomycosis)

  • Caused by various species of filamentous fungi, including Microsporum, Epidermophyton, and Trichophyton spp.
  • These fungi are collectively referred to as dermatophytes
  • Ringworm infections have nothing to do with worms
• Subcutaneous mycoses


  • Most often caused by traumatic implantation of the fungus into the subcutaneous tissue by soil or plant fungi
  • Slowly developing infection
• Chromoblastomycosis of the Foot—also called Phaeohyphomycosis


  • Most often caused by dematiaceous fungi that have melanin in their cell walls
  • Often appear in tissue as sclerotic bodies (muriform cells) that are chestnut brown in appearance and have crosswalls in multiple planes
• Coccidioidomycosis (Valley Fever)


  • Coccidioides immitis/pasadasii, a dimorphic fungus
  • Transmission occurs via inhalation of arthrospores
  • Mainly in California, Arizona, New Mexico, and West Texas
• Cryptococcosis


  • Two species of Cryptococcus—C. neoformans and C. gattii, encapsulated yeast
  • Transmission occurs via inhalation of yeasts in soil contaminated with bird droppings
  • C. gattii is associated with trees (esp. Eucalyptus in Pacific Northwest)
• Histoplasmosis


  • Histoplasma capsulatum var. capsulatum, a dimorphic fungus
  • Transmission occurs via inhalation of conidia from soil, bat guano, pigeon droppings
  • Worldwide; in the United States, mainly in Mississippi and Ohio River valleys
• Coccidioides immitis/posadasii


  • Spherules with endospores in tissue
  • Mould form with alternating arthrococcidia
• Histoplasma capsulatum


  • Cluster of Histoplasma yeast in heart valve tissue by PAS stain
  • Tuberculate macroconidia of Histoplasma in culture
• Pneumocystis Pneumonia (PCP or PJP; Interstitial Plasma-Cell Pneumonia)


  • Caused by Pneumocystis jirovecii, which has both protozoal and fungal properties
  • Mostly occurs in the immunocompromised host
  • Was once classified as a protozoan, but is now classified as a fungus
  • Mode of transmission is unknown; perhaps direct contact, transfer of pulmonary secretions from infected to susceptible persons, or perhaps airborne
• Pneumocystis jirovecii in lung tissue by silver stain


  • Organisms appear black
• Thrush


  • A yeast infection of the oral cavity
  • Common in infants, elderly patients, and immunosuppressed individuals
  • White, creamy patches occur on the tongue, mucous membranes, and the corners of the mouth
  • Caused by Candida albicans and related species
• Yeast Vaginitis


  • Most cases are caused by the yeast, Candida albicans
  • Can be diagnosed by microscopic examination of a saline wet mount of vaginal discharge material, in which numerous yeasts, hyphae, and pseudohyphae may be observed
  • The mere presence of yeast is not proof of yeast vaginitis, as the vaginal flora of up to 25% of healthy women can contain Candida spp.
• Cryptococcal Meningitis


  • Can be caused by Cryptococcus neoformans, an encapsulated yeast
  • Cryptococcosis starts as a lung infection, but spreads via the bloodstream to the brain
  • Cryptococcal meningitis can be presumptively diagnosed by observing encapsulated, budding yeasts in CSF specimens examined by an India ink preparation, Gram stain, or by immunodiagnostic methods
  • Most often seen in immunocompromised patients and the elderly
• Gram-Stained Appearance of Cryptococcus

  • Yeast
  • Capsule
• Infections Caused by Microsporidia

  • Diarrhea
  • Keratitis
  • Keratoconjunctivitis
  • Corneal ulcer
  • Myositis, myocarditis
  • Urinary tract infection
  • Disseminated infection in immunocompromised patients
• Appropriate Therapy for Fungal Infections

  • Three major classes of antifungal agents are used to treat systemic and opportunistic fungal infections:
  • Amphotericin and liposomal amphoteracin
  • Azoles such as fluconazole, ketoconazole, voriconazole
  • Echinocandins such as caspofungin, micafungin
  • Terbinafine and griseofulvin are used for treatment of dermatophyte infections