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Bact > Test 3- Intro To Fungi and Funigal Infections > Flashcards

Test 3- Intro To Fungi and Funigal Infections Flashcards

1
Q

Taxonomy of Fungi

A

• About 1.5 million species in the Kingdom Fungi

  • >80,000 described
  • ~400 are known human/animal pathogens
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2
Q

General Characteristics of Fungi

A

• Eukaryotic!- so are we- have to be careful when treating
• Non‐photosynthetic

  • Heterotrophic
  • General taxonomy is constantly in flux
  • Several Phyla
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3
Q

General Characteristics

A

Non‐motile (usually)

Aerobic (usually)

• Some yeast forms may ferment anaerobically

Spore‐bearing

Cell Wall

  • Chitin, cellulose, proteins, and lipids (ergosterol- sterol that we use as a target for drugs)
  • Provides rigidity and osmotic stability

Capsule- can be a defining characterisitic
• Polysaccharides

  • Greatly variable in thickness
  • May be antigenic and/or antiphagocytic

Unicellular species or forms

• YEAST

Multicellular species or forms

• MOLDS and MUSHROOMS

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4
Q

Yeast

A
  • Oval or spherical cells
  • 3‐5 um in diameter
  • Unicellular

• Some variability in form
———–Some form chains known as pseudohyphae

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5
Q

Molds

A

Molds

  • Main element (tubular structure) of the vegetative or growing form is the HYPHAE
  • Can be divided by cross‐walls called septa

—————-Septate vs. non‐septate (coenocytic)

• Pigmentation
———-Dark pigment (Dematiaceous)

——— Non‐pigmented (Hyaline)

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6
Q

Dimorphic Fungi

A

• Change from mycelial form (at room temperature) to yeast (at 37°C or in the tissues of animals)

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7
Q

Fungal Reproduction

A

Sexual: NOT COMMON

  • Only demonstrated in a few fungi
  • Fusion of two haploid nuclei followed by meiotic division of the diploid nucleus

Asexual:
• Very common and effective

  • Division of nuclei by mitosis
  • Three mechanisms:
  • Sporulation followed by germination of the spores

——————– Aspergillus and Penicillium

• Fragmentation of hyphae

————-Coccidioides immitis

• Budding of yeast cells
————Candida and Cryptococcus

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8
Q

Fungal Infections

A

• Rarely cause disease in healthy, immunocompetent animals

————-Except dermatophytes(ring worm)

Factors which may predispose to fungal invasion of tissues:

  • Immunosuppression
  • Prolonged antibiotic therapy
  • Immunological defects
  • Immaturity, ageing and malnutrition
  • Exposure to heavy challenge of fungal spores
  • Traumatized tissues
  • Persistent moisture on skin surface
  • Some neoplastic conditions
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9
Q

Immunity to Fungal Infections

A

• Immunity is mainly cell‐mediated

—————–Antibodies are usually produced (Except with superficial dermatophyte infections)

———————– Antibodies are not protective
• Most lesions are granulomatous

————— Resemble mycobacteriosis and other diseases caused by facultative intracellular bacteria

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10
Q

Isolation of Fungal Organisms

A

• Most grow in common media at 20‐25°C

———————- Sabouraud’s dextrose (SabDex) agar

• Some grow in Blood agar in the yeast phase at 37°C

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11
Q

Dermatophytes

A
  • Molds capable of parasitizing only keratinized epidermal structures
  • Superficial skin, hair, feathers, horns, hooves, claws and nails

loss of hair around the eyes, nose; not itchy in dogs and cats; only in humans

• Dermatophyte infections are called dermatophytosis or ringworm

• ZOONOSIS

• Several causative agents:

• Microsporum
• Trichophyton
• Epidermophyton

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12
Q

Ecology

A

Anthropophillic- HUMANS- not transmitted to animals

Zoophilic- Animals- can be transmitted to humans

M. canis

Geophilic- can be transmitted to humans

M. Gypseum

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13
Q

General Characteristics of Dermatophytes

A
  • Phylum Ascomycota
  • Grow slowly on SabDex

——–Produce pigmented colonies( white, yellow, or tan)

• Septate hyphae

General Characteristics

• Produce macroconidia and microconidia in culture(not if you take a hair from a cat or a fresh sample)

  • Macroconidia are most useful for identification
  • Microsporum: large, septate, rough, thick‐walled, fusiform or obovate macroconidia

• Trichophyton: cylindrical or cigar‐shaped, smooth, thin‐ or thick‐walled macroconidia(can be confused with demodex)

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14
Q

Virulence and Pathogenesis

A
  • Proteolytic enzymes (e.g. keratinase, elastase and collagenases)
  • Synergistic action with some bacteria (e.g. Staphylococcus spp.)- make sure you get the staff under control
  • Infective arthrospores adhere to keratinized structures
  • Favorable environmental conditions (trauma, moisture, warmth) encourage germination
  • Hyphae grow centrifugally producing the typical ‘ringworm’ lesion depending on the local inflammatory response

• Transmission is mainly through direct contact
• Indirect by fomites or environmental contamination may also occur

• In the parasitic state only hyphae and arthroconidia (arthrospores) are seen

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15
Q

Pathology

A

• Initial phase: subclinical or mild host response
• Hypertrophy of the stratum corneum with accelerated keratinization and exfoliation

• Scruffy appearance and some hair loss (alopecia)

• Later phase: more pronounced inflammatory response

  • Ranges from erythema to vesiculopustular reactions and suppuration
  • Roughly circular pattern of the lesions and their inflamed margins suggested the terms ringworm and tinea
  • Ringworm usually regresses spontaneously within a few weeks or months
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16
Q

Laboratory Diagnosis

A

Initially based on assessment of source (host animal, lesion appearance, etc.)

In cats and dogs, examination of lesions with a Wood’s lamp is helpful

• Filtered UV light
• M. canis often will fluoresce green due to a tryptophan metabolite
• 50‐60% of infected animals will be positive- if you don’t see the flourescence, it doesn’t mean that is isn’t there

Skin scraping and hair examination

• Observe for hyphae and arthroconidia

ECTOTHRIX(hang on to the hair shaft)

17
Q

Laboratory Diagnosis

A
  • Include material from the margins of any lesion- WANT THE ACTIVE EDGE OF THE LESION
  • 10‐20% potassium hydroxide and heated gently

———— Treatment clears sample and allows better microscopic examination (100x)

• Stains may improve visualization

  • ————– Permanent ink, lactophenol cotton blue, dimethylsulfoxide
  • —————-Calcofluor white reagents imparts fluorescence to fungal structures
18
Q

Culture

A

• Sabouraud’s dextrose (SabDex) agar at 25°C for up to 3 weeks

———–Cycloheximide, tetracycline or chloramphenicol can be added

• Dermatophyte Test Medium (DTM)

  • ———Phenol Red indicator
  • ——– Beware of false positives
  • Rapid Sporulation Medium (RSM)
  • (Molecular techniques)

Culture

19
Q

Treatment and Control

A

• Isolate infected animals

• Systemic therapies:

  • Itraconazole
  • Griseofulvin
  • Terbinafine
  • Fluconazole

————— beware of teratogenicity in the systemic therapies

Treatment and Control

• Lime sulfur or miconazole shampoo

• Clip hair, especially for extensive lesions
————–Dispose of hair carefully because of infective arthrospores

  • Contaminated bedding should be discarded (burned) and grooming equipment disinfected (0.5% sodium hypochlorite)
  • Vaccines have not been effective in dogs/cats
20
Q

Dermatophytosis in Other Species

A

Cattle
• T. verrucosum
• Usually affects calves
• Commercial vaccines used successfully in Europe and Russia

Horses
• T. equinum, M. canis (=M. equinum); rarely M. gypseum, T.

mentagrophytes, and T. verrucosum

Young horses, associated with tack and grooming gear

Limited vaccination in Europe

Pigs
• M. nanum (uncommon)
• No age predilection, no current economic significance

Poultry
• M. gallinae

  • Avian ringworm or favus
  • Often affects the comb and wattles, but may invade feather follicles
21
Q

Treatment of Fungal Infections

A

Systemic antifungals- Side Effects!!!

Griseofulvin- don’t use in preganant animals

Bact (34 decks)

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