Mycology Part 1A

Question 1

How are specimen collected for Cutaneous Mycoses? (I.e. Ringworm)

Answer 1

1. Clean area with alcohol
2. Collect hair by plucking from periphery of lesions
3. Use edge of scalpel for skin scrapings
4. Place in envelope or sterile petri dish

• Do not use tightly sealed containers

Question 2

How are specimen collected for systemic and subcutaneous Mycoses?

Answer 2

1. Collect exudate or material from edge of lesion
2. Place in sterile, leak proof test tube for direct examination and culture

Question 3

What is a Woods Lamp?

Answer 3

• Diagnostic method in mycology
• UV light - 366nm
• Yellow-green fluorescence of infected hairs or skin
• False positive with some medications

Question 4

Which dermatophytes fluoresce under Wood’s Lamp?

Answer 4

• Microsporum canis - animals
  
  • 80% of ringworm in dogs and cats
• M. distortum - humans
• M. ferrugineum - humans
• M. audouinii - humans

Question 5

How is Direct Examination of Mycoses work?

Answer 5

1. Place sample on a slide with a few drops 10% NaOH or KOH
2. Incubate for 15-30 minutes in a moist chamber
3. Look for hyphae, arthrospores - Endothrix or Ectothrix spores

• False positives: oil or grease droplets

Question 6

How are wet preparations (pus, exudates, etc) directly examined?

Answer 6

1. Wet mount with New Methylene Blue or Lacto-Phenol Cotton Blue
2. Stain with Gram, Geimsa, or other special stains
   
   1. Cryptococcus- India Ink preparations of CSF - thick capsule

Question 7

What media should be used for the isolation of fungus?

Answer 7

• Dependent on the suspected fungus
  
  • Sabouraud Dextrose Agar: pH 5.6
    
    • Inhibits many species of bacteria
  • Sabouraud/Cycloheximide/Chloramphenicol
    
    • Inhibits many bacteria and contaminating fungi
  • Dermatophyte Test Medium (DTM)
    
    • Dermatophytes - Red - Alkaline
    • Other Fungi - Yellow - Acid
  • Potato Dextrose Agar
    
    • Sporothrix schenkii - Black Colonies

Question 8

How should fungi be incubated?

Answer 8

• Moist atmosphere to prevent drying of plates
• Incubate at room temperature or 25C
  
  • 30 C for Candida spp
  • T. verrucosum (bovine ringworm) 37C
  • Diphasic fungi
    
    • yeast or tissue form 37C
    • Mycelial form 25C

Question 9

What Biochemical Tests are available for Candida species?

Answer 9

• Sugar fermentation
• Sugar assimilation
• Commercial test kits - API system

Question 10

What Immunologic Test are available for fungi?

Answer 10

• CMI response
  
  • usually done by skin testing (Type IV hypersensitivity)
• Humoral response
• Histoplasmosis -AGID
• Blastomycosis - AGID
• Coccidioidomycosis -AGID
• Cryptococcosis - Latex Agglutination
• Aspergillosis - AGID

Question 11

What are fungi Opportunists?

Answer 11

• May be primary or secondary pathogens under appropriate conditions
  
  • Old, young, immunocompromised
  • Individuals of low resistance
  • Individuals on long term hormone, antibiotic, or steroid therapy
  • Individuals who are debilitated

Question 12

What are the significant Fungi Species?

Answer 12

• Mucor spp.
• Rhizopus spp.
• Absidia spp
• Aspergillus spp.
• Alternaria spp.
• Penicillium spp.
• Geotrichum spp.
• Fusarium spp.

Question 13

What is Dermatomycosis?

Answer 13

• Cutaneous Mycoses
• Live on superficial parts of the host
• Non-Invasive
• Usually will not survive long in living tissue
• Will NOT survive in areas of intense inflammation
• Have Keratolytic activity

Question 14

What is the Geographic Distribution of Dermatomycosis?

Answer 14

• World Wide
• More prevalent in tropical and sub-tropical climates
• Particularly prevalent in hot humid areas

Question 15

What is the Prevalence of Dermatomycosis?

Answer 15

• Microsporum canis associated with:
  
  • >90% of all Feline Ringworm
  • >70% of all Canine Ringworm

Question 16

What is the pathogenesis of Dermatomycosis?

Answer 16

• Dermatophyte contacts skin of animal:
  
  • Brushed off
  • Competes with bacterial flora
  • Set up residence and produce carrier state - cats
  • Set up residence, multiply, and produce disease
  • Excretes toxins or irritants which are generally protein in nature
  • Elastase, Collagenase, Keratinase
  • Survival dependent upon mutual existence
  • Local inflammation is due to galactomannan glycopeptides
  • Excessive inflammation results in:
    
    • Peripheral movement of the fungus
    • Typical ring lesion

Question 17

What are the Clinical Manifestations of Dermatomycosis?

Answer 17

• Extremely variable:
  
  • Eruptive lesion (Kerion)
  • May be mixed with Staphylococcus spp.
  • Ringed lesions in animals not common

Question 18

How does Dermatomycosis affect Dogs and Cats?

Answer 18

• M. canis most common
• Dogs:
  
  • Face, extremities, lower abdominal wall
  • Crusty alopecic lesions
• Cats:
  
  • Ears, face, extremities
  • Crusty alopecic lesions, a minimum of erythema

Question 19

How does Dermatomycosis affect cattle?

Answer 19

• T. verrucosum - 99+%
• Crusty, plaque-like lesions on face and neck

Question 20

How does Dermatomyosis affect sheep?

Answer 20

• Trichophyton spp. - most common
• Crusty lesions on shoulders, neck, and chest

Question 21

How does Dermatomycosis affect Horses?

Answer 21

• T. equinum and T. mentogrophytes - Most common
• Deep scaly ulcerating lesions

Question 22

How does Dermatomycosis affect swine?

Answer 22

• M. namum most common
• Reddish-brown, ringed lesion on lower abdominal wall

Question 23

How does Dermatomycosis affect Poultry?

Answer 23

• T. gallinae - most common
• Crusty, scaly lesions most evident on comb and wattles

Question 24

How is Dermatomycosis Diagnosed?

Answer 24

• Clinical Diagnosis:
  
  • Wood’s Lamp Examination - 366 nm
    
    • Limited value
    • False positive - medication
    • False negative
      
      • Not all M. canis fluoresce
      • spores may be subcutaneous
• Laboratory Diagnosis:
  
  • Direct Microscopic examination
    
    • Observe arthrospores
  • Cultural examination
    
    • Incubate at room temp (25C) for 2-4 weeks

Question 25

Is Dermatomycosis Zoonotic?

Answer 25

• Animal ringworm rarely spreads to humans
• Route of infection:
  
  • Direct, indirect or airborne rare
  • Spores viable for years on fomites

Question 26

How is Dermatomycosis treated?

Answer 26

• 5 Mechanisms of action
  
  • Irritants - invoke inflammatory response
  • Keratolytics - remove stratum corneum
  • Fungicidal agents
  • Fungistatic agents
  • Vaccine for T. verrucosum - Live
    
    • attenuated - Europe

Question 27

What are the important Antifungal Agents?

Answer 27

• Amphotericin B
• Nystatin, Natamycin
  
  • Affects permeability
  • Hemolytic anemia
  • Renal toxicity
• 5-Fluorocytosine
  
  • Fungal RNA - Errors
• Imidazoles / Triazoles
  
  • Cell wall
  • Cell membrane
  • Nutrient uptake
• Griseofulvin
  
  • Chitin wall
  • Inhibits nucleic acid synthesis
• Sulfur compounds
• Salicylic acids
• Fatty acids
• Benzoic acid
• Phenoll
• Tincture of Iodine
• Organic Iodine compounds as soaprs