Medical Mycology

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MEDICAL MYCOLOGY Arthur F. Di Salvo, MD Reno,
Nevada
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Medical Mycology Outline

• HOUR SUBJECT
• Introduction, Actinomycetes
• Yeasts, Dermatophytes
• Filamentous Fungi, Dimorphic Fungi
• Dimorphic Fungi
• Opportunistic Fungi

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OBJECTIVES

• To impart sufficient basic science of the
  medically important fungi to assist you in
  diagnosing mycotic diseases.
• To impart sufficient clinical knowledge
• to raise your index of suspicion for mycotic
  diseases.

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• What is SAID is not HEARD
• What is HEARD is not UNDERSTOOD
• What is UNDERSTOOD is not RETAINED
• What is RETAINED is not IMPLEMENTED

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• ASK QUESTIONS ANYTIME

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INTRODUCTION
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Fairy Ring Mushrooms
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What is Mycology?
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Mycology is the study of

• Beer
• Wine
• Bread
• Cheese
• Gourmet mushrooms
• Environmental toxins
• Biodegradation
• Disease

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BIOREMEDIATION

• Oil spills
• Cyanide in mining operations
• Dioxins and pesticides
• Produce organic acids, sugars
• Other commercial products

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A. Classification
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What is a Fungus ?

• Eukaryotic a true nucleus
• Do not contain chlorophyll
• Have cell walls
• Produce filamentous structures
• Produce spores

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Species of Fungi

• 100,000 200,000 species
• About 300 pathogenic for man

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Kingdom Fungi Eukaryocytes

• Ascomycota
• Basidiomycota
• Zygomycota
• Mitosporic Fungi
• (Fungi Imperfecti)

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SIZE COMPARISON OF PATHOGENS
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Actinomyces(True Bacteria)

• Tradition
• Clinical infection resembles mycoses
• Actinomyces grow on mycotic media
• Actinomyces grow slowly (24-48 h)
• Gross colonies resemble fungi
• (rough,heaped, short aerial filaments)
• Resemble mycelia microscopically, with branched
  mycelia in tissue and smears.

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HANDOUT

• Page 2

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What is Medical Mycology ?
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MYCOTIC DISEASES(Four Types)

• Hypersensitivity
• Allergy
• Mycotoxicosis
• Production of toxin
• Mycetismus (mushroom poisoning)
• Pre-formed toxin
• Infection

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Hypersensitivity

• FARMERS LUNG Moldy hay
• MALT WORKERS DISEASE Moldy barley
• CHEESE WASHERS LUNG Moldy cheese
• WOOD TRIMMERS DISEASE Moldy wood

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PATHOGENIC FUNGI

• NORMAL HOST
• Systemic pathogens - 25 species
• Cutaneous pathogens - 33 species
• Subcutaneous pathogens - 10 species
• IMMUNOCOMPROMISED HOST
• Opportunistic fungi - 300 species

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PARASITIC STATE

• Increased metabolic state
• Modified metabolic pathways
• Modified cell wall structure
• Carbohydrate content
• Lipid structure
• RNA aggregates

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PATHOGENICITY OF FUNGI

• Thermotolerance
• Ability to survive in tissue environment
• Ability to withstand host defenses

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REVIVED INTEREST IN MYCOLOGY

• Increased frequency of mycotic diseases
• Increased awareness by physicians
• Better trained laboratory personnel
• More invasive procedures used on patients
• Increased use of immunosuppressive drugs
• Increase in immunosuppressive disease
• 7. Better laboratory diagnostic tools

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B. MORPHOLOGY
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MORPHOLGY

• Yeasts
• Hyphae (filamentous fungi, mycelium)
• Septate
• Coenocytic (non-septate)
• Dimorphic
• Yeast
• Mycelium

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Dimorphic Fungi

• Yeast Form
• Parasitic form
• Tissue form
• Cultured at 37 C
• Mycelial Form
• Saprophytic form
• Cultured at 25 C

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SPORES

• SEXUAL
• ASEXUAL
• Arthrospore
• Blastospore
• Chamydospore
• Conidia
• Microconidia
• Macroconidia

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By their fruits ye shall know them

• Mathew 720

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EPIDEMIOLOGY

• PAGE 3

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• MOST MYCOTIC AGENTS
• ARE SOIL SAPRPHYTES

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ECOLOGICAL ASSOCIATION

• PATHOGEN HUMAN SOIL
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• Blastomyces dermatitidis 1898 1964
• Cryptococcus neoformans 1894 1951
• Coccidioides immitis 1900 1932
• Histoplasma capsulatum 1934 1949

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Mycotic Diseases Are NOTContagious
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ESTABLISHMENT OF INFECTION WITH A MYCOTIC AGENT
DEPENDS ON

• Inoculum size
• Resistance of the host

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THE CLINICIAN MUST DISTINGUISH BETWEEN

• COLONIZATION
• FUNGEMIA
• INFECTION

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GEOGRAPHIC DISTRIBUTION

• The present ease and frequency of world-wide
  travel make it more likely that physicians in the
  United States will be confronted with a variety
  of unfamiliar mycoses acquired in distant parts
  of the country or of the world.

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Endemic Mycoses

• Those fungus infections with a limited geographic
  distribution. They are all caused by dimorphic
  fungi

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PATIENT HISTORY

• Medical
• Travel
• Occupation
• Avocation

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D. DIAGNOSIS
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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA
probes
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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA
probes
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DIRECT MICROSCOPIC OBSERVATION

• 10 KOH
• Gentle Heat

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KOH Wet Mount
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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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SKIN TESTING(DERMAL HYPERSENSTIVITY)

• Use is limited to
• Determine cellular defense mechanisms
• Epidemiologic studies

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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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FUNGI ARE POOR ANTIGENS
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FUNGAL SEROLOGYANTIBODIES

• Latex Agglutination IgM
• Immunodiffusion IgG
• Complement Fixation IgG

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Most serological tests for fungi measure
antibody. Newer tests to measure antigen are now
being developed

• ANTIGEN DETECTION PRESENTLY AVAILABLE
• Cryptococcosis
• Histoplasmosis
• Aspergillosis

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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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DIRECT FLUORESCENT ANTIBODYCAN BE APPLIED TO

• HISTOLOGIC SECTIONS
• CULTURE
• Viable organisms
• Non-viable organisms

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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probe
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INFLAMMATORY REACTION

• Normal host
• Pyogenic
• Granulomatous
• Immunodeficient host
• Necrosis

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Polymorphic Nuclear Leukocytes
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Giant Cell
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GMS
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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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ISOLATION MEDIA

• SABOURAUD DEXTROSE AGAR
• (pH 5.6)
• Plain
• With antibiotics
• With cycloheximide

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INCUBATION TEMPERATURE

• 37 C - Body temperature
• 25 C - Room temperature

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Diagnosis1. Wet Mount2. Skin
test3. Serology4. Fluorescent antibody5.
Biopsy and histopathology6. Culture7. DNA probes
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DNA Probes

• Rapid (1-2 Hours)
• Species specific
• Expensive

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E. TREATMENT
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THERAPY

• Because they are eukaryotic, fungi are
  biochemically similar to the human host.
  Therefore it is difficult to develop
  chemotherapeutic agents that will destroy the
  invading fungus without harming the patient.

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A BASIC TENET OF PATHOLGY

• A CAUSE OF IRREVERSIBLE CELL INJURY IS CELL
  MEMBRANE DAMAGE.

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IN FUNGAL THERAPY

• We attempt to induce cell injury by causing
  the cell membrane of the fungus to become
  permeable.

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PROBLEM

• Finding an agent that will selectively injure
  fungal cell walls without damaging the host cell.

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ALL EUKARYOTIC CELLS CONTAIN STEROLS

• Mammalian cells cholesterol
• Fungal cells - ergosterol

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PRIMARY ANTI-FUNGAL AGENTS

• Polyene derivatives
• Amphotericin B
• Nystatin
• Azoles
• Ketoconazole
• Fluconazole
• Itraconazole
• Voriconazole
• Posaconazole

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AMPHOTERICIN BMechanism of Action

• Amphotericin B binds to sterols
• Ergosterol is a constituent of the fungal cell
  wall
• AMB has a greater avidity for ergosterol than for
  the cholesterol in the human cell wall
• Binding to the fungal cell wall alters the
  permeability and the intracellular contents leak

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AMPHOTERICIN BDisadvantages

• Intravenous administration
• Thrombophlebitis
• Nephrotoxic
• Fever
• Chills
• Anemia
• Long term administration

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Azoles

• There are a few rare serious side effects from
  Itraconazole and Fluconazole

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PRIMARY ANTI-FUNGAL AGENTS

• 3. Griseofulvin
• 4. 5-fluorocytosine (5-FC)
• 5. Allylamines
• -Terbinafine (Lamasil)
• 6. Echinocandins
• - Caspofungin

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Griseofulvin

• A slow acting drug used for skin and nail
  infections. It accumulates in the stratum
  corneum and prevent hyphal penetration through
  these layers

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5-fluorocytosine(5-FC)

• Interferes With RNA Synthesis

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MECHANISMS OF ACTION

• Polyenes
• Azoles
• Griseofulvin
• 5 - FC

• Ergosterol in cell membrane
• Interfere with ergosterol synthesis
• Forms a barrier to fungal growth
• Inhibits RNA synthesis

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F. Clinical Classification of Mycoses

• Cutaneous
• Subcutaneous
• Systemic
• Opportunistic

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Cutaneous Mycoses

• Skin, hair and nails
• Rarely invade deeper tissue
• Dermatophytes

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Subcutaneous Mycoses

• Confined to subcutaneous tissue and rarely spread
  systemically. The causative agents are soil
  organisms introduced into the extremities by
  trauma

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Systemic Mycoses

• Involve skin and deep viscera
• May become widely disseminated
• Predilection for specific organs

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OPPORTUNISTIC FUNGI

• Ubiquitous saprophytes and occasional pathogens
  that invade the tissues of those patients who
  have
• Predisposing diseases
• Diabetes, cancer, leukemia, etc.
• Predisposing conditions
• Agammaglobulinemia, steroid or
  antibiotic therapy.

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Medical Mycology Iceberg
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THE ESSENTIAL ELEMENT OF DIAGNOSIS IS

• A HIGH INDEX OF SUSPICION !

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End of Introduction