08 - Mycology Review Flashcards
Describe the clinical and epidmiological significance of cutaneous mycoses (aka dermatophytoses)
Clinical: Characterized by itching and scaling skin patches with possible inflammation and weeping.
Epidemiology: Infections occur from anthropophilic (residing on human skin), zoophilic (residing on skin of domestic and farm animals), and geophilic (residing in soil) mycoses. Transmission is human-to-human, animal-to-human, or by contact with infected skin scales on inanimate objects.
Identified based on location: tinea capitis (scalp; scalp ringworm), tinea corporis (trunk; ring worm), tinea pedis (feet; athlete’s foot), tinea unguium (nails), tinea cruris (groin; jock itch).
Describe the clinical and epidmiological significance of subcutaneous mycoses
Clinical: Infect dermis, subcutaneous tissue, and bone.
Epidemiology: Acquired through traumatic lacerations or puncture wounds (eg thorns while gardening), usually in tropical climates. Fungi reside in soil (geophilic) or decaying vegetation. Not transmissible human to human.
Describe the clinical and epidmiological significance of systemic mycoses
Clinical: Often mild and self-limiting in otherwise healthy patients, but can be life threatening in immunosuppressed patients.
Epidemiology: Contracted by inhalation of airborne spores from aerosolized soil, germination takes place in the lungs, can spread to any organ. Closely associated with geographic region:
Blastomycosis: South central and SE US (the blasted south).
Coccidioidomycosis: SW US (Mr. Fungus cocks his pistol in the old SW).
Histoplasmosis: Ohio/MS River Valley (lots of s’s).
Paracoccidioidomycosis: Central and South America.
Describe the clinical and epidmiological significance of opportunic mycotic infections
A subtype of systemic mycotic infections in immunocompromised patients (infants, HIV, cancer).
Describe and discuss the key characteristics that identify pahologic fungal organisms
Eukaryotes: Membrane enclosed nucleus. Humans are also eukaryotes, bacteria are prokaryotes.
Cell walls: Made of chitin (bacterial cell walls use peptidoglycan); unaffected by antibiotics.
Ergosterol: Defining characteristic of fungal cell membranes (human cell membranes use cholesterol); target for antifungal drugs.
Heterotrophs: Require pre-formed source of carbon for growth, secrete degradative enzymes.
Saprophytic: Obtain nourishment from dead organic matter.
Parasitic: Obtain nourishment from live organic matter (some species).
Describe the life cycle of each of the major types of fungi and how infection is acquired by humans
Big picture: All fungi reproduce by sporulation. Most pathogenic fungi use asexual sporulation.
Filamentous mold (mutli-cellular): Thread-like hyphae grow by branching and tip elongation to form a mass (mat-like structure) called mycelia.
Yeast-like fungi (unicellular): Single, unconnected spheroid cells (like bacteria but 10x larger). Asexual reproduction by budding.
Dimorphic: Fungi able to grow as yeast or mold depending on environment (temperature and CO2 levels), common in fungi causing systemic mycotic infections.
Distinguish among the major fungal groups in terms of their pathogenic mechanisms: cutaneous mycoses
Dermatophytes that infect the epidermis secrete the enzyme keratinase (utilize keratin as energy source).
Spread: Human-human, animal-human, contact with infected skin scales.
Examples: Microsporum, trichophyton, epidermophyton.
Distinguish among the major fungal groups in terms of their pathogenic mechanisms: subcutaneous mycoses
Exploits an opening in skin after trauma (laceration, puncture) to gain entrance to the body. Infect dermis, subcutaneous tissue, and bone.
Spread: Soil/decaying vegetation-human, NOT human-human.
Examples: Sporothrix schenckii (ulcerated nodules along lymph path), cladosporium (large, wart-like lesions).
Distinguish among the major fungal groups in terms of their pathogenic mechanisms: systemic mycoses
All dimorphic. Infections often asymptomatic, chronic pulmonary and dissemination to other organs.
Spread: Aerosolized spores, NOT human-human.
Examples: Blastomyces, histoplasma, coccidioides, paracoccioides.
Distinguish among the major fungal groups in terms of their pathogenic mechanisms: opportunistic mycoses
Subtype of systemic. Infection/symptoms more severe due to decreased immune status of host.
Spread: Depends. Aspergillus is inhaled dust. Candida is normal flora overgrowth. Pneumocystis jiroveci is activation of dormant cells in lungs.
Describe and discuss the signs and symptoms, pathogenesis, diagnostic workup, and management of infection with Trichtophyton sp. (including Tinea strains) (Table 1.8.1)
Pathogenesis: Parasitize epidermis including hair and nails, causing morbidity called superficialis. Uses kertinase to break down the epidermis.
Signs/symptoms: Infection on epidermis, annular skin lesions, scaling and macerations of affected areas, alopecia, pruritis.
Diagnostic workup: Direct examination and fungal culture from lesions of skin, around hair, and shavings of nails.
Management: Topical antifungal agent (thiocarbamates, imidazoles, allylamine, and morpholines). Oral antifungal agents (ketoconazole, itraconazole, fungusbinafine).
Describe and discuss the signs and symptoms, pathogenesis, diagnostic workup, and management of infection with Sporothrix schenckii (Table 1.8.1)
Pathogenesis: Infection is through skin laceration or puncture especially by rose throrn. Dissemination is common in immunocompromized patients.
Signs/symptoms: Infection characterized by granulomatous ulcer at the site of injury.
Diagnostic workup: Blood culture.
Management: Itroconazole, Terbinafine.
Describe and discuss the signs and symptoms, pathogenesis, diagnostic workup, and management of infection with Histoplasma capsulatum (Table 1.8.1)
Pathogenesis: Spores enter the lung and germinate into yeast-like cells. Macrophages engulf these cells. Pulmonary infections may be acute, chronic or fatal.
Signs/symptoms: Asymptomatic. Often resembles TB (persistent cough, constant fatigue, weight loss, fever, coughing up blood, night sweats). Diagnostic workup: Blood culture. Urinalysis for exo-antigen).
Management: Oral antifungal agent (Ketoconazole, Amphotericin B, Fluconazole).
Describe and discuss the signs and symptoms, pathogenesis, diagnostic workup, and management of infection with Blastomyces dermatitidis (Table 1.8.1)
Pathogenesis: Microspores enter the lung and germinate into thick-walled yeast-like cells. Appear unipolar, broad-base buds. Disseminates 70% from the lungs into the skin.
Signs/symptoms: Asymptomatic. Often resembles TB (persistent cough, constant fatigue, weight loss, fever, coughing up blood, and night sweats).
Diagnostic workup: Isolation and culture of blood for the fungus.
Management: Oral antifungal agent (Ketoconazole, Amphotericin B, Fluconazole, etc).
Describe and discuss the signs and symptoms, pathogenesis, diagnostic workup, and management of infection with Candida sp. (Table 1.8.1)
Pathogenesis: C. albicans most common species. Oral, vaginal, or systemic opportunistic infections develop in immunocompromised states.
Signs/symptoms: Oral - white raised plaques on oral mucosa and tongue, vaginal - white, cottage cheese-like discharge, itching and burning pain on vulva, systemic - can affect GI tract, kidneys, liver, spleen.
Management: Oral and vaginal topical treatments (nystatin or clotrimazole). Azole (oral), (if severe) ketoconazole, fluconazole, itraconazole. (If systemic) Amphotericin B occasionally with flucytosine.
