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Infectious Agents 2 > Mycology Exam Objectives > Flashcards

Mycology Exam Objectives Flashcards

1
Q

What is the infectious particle for Blastomyces dermatitidis?

A

Microconidia produced by mycelial form in soil

- is inhaled, penetrates wounds, or possibly ingested

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2
Q

Infectivity of Blastomyces dermatitidis

A

Not contagious or transmissible, not zoonotic!

  • common environmental source if in more than 1 animal in a household
  • vets may be infected from patients (common w/ open wounds) or from necropsy by handling infected tissues
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3
Q

What is the infectious particle for Histoplasma capsulatum?

A

Microconidia produced by mycelial form in soil

- disseminated by wind, easily inhaled/ingested

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4
Q

Infectivity of Histoplasma capsulatum

A
  • aerosols from digging, chain saws, birds roosting on air conditioners have led to epidemics
  • not transmissible, not zoonotic –> in vivo yeast phase does not survive long if shed from active infection (inclu. feces)
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5
Q

What is the infectious particle for Coccidioides immitis?

A

Arthroconidia (conidia)

  • disseminated by dust storms, rodents, excavations
  • inhalation, or may be inoculated into skin
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6
Q

Infectivity of Coccidioides immitis

A

Most virulent of all fungal pathogens!

- only a few conidia are required to produce infection

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7
Q

Infectivity of Sporothrix schenckii

A

Not contagious, but infected animal will serve as source of contamination of the environment

  • people have been infected from cats
  • cats may shed viable organisms in feces
  • occupational disease of gardeners and florists
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8
Q

What is the infectious particle of zygomycetes?

A

Conidia

- inhalation, percutaneous routes, ingestion of conidia

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9
Q

What are the 2 orders of zygomycetes?

A

Mucorales and Entomophthales

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10
Q

Mucorales

A

Rhizopus, Mucor, Rhizomucor, Absidia, Cunninghamella, Mortierella, Syncephalatrum
- occur rarely, in immunocompromised hosts as opportunistic infection

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11
Q

Entomophthorales

A

Occurs in tropical and subtropical regions

  • transmission via implantation of spores thru cutaneous trauma (insect bite, foreign bodies) and by inhalation of spores
  • true pathogens! –> infect immunocompetent hosts
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12
Q

Infectious particles of Cryptococcus neoformans

A

Yeast cells

- found in surface dust and dirt, are inhaled and deposited on mucous membranes of nasal cavity

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13
Q

Infectious particle of Pythiosis

A

Aquatic, motile biflagellated spores

- ingested when a dog or horse drinks contaminated water

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14
Q

What is the most common manifestation of Blastomyces dermatitidis?

A

Pulmonary form!

  • does not spontaneously resolve
  • chronic respiratory problem with weight loss, fever that is non-responsive to antibiotics, dry (non-productive) cough, ocular problems, lameness, lymphadenopathy, pulmonary interstitial pattern that resembles tuberculosis (snow storm)
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15
Q

Which 2 fungi have pulmonary forms that spontaneously resolve?

A

Histo and coccidiomycosis!

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16
Q

Ocular form of Blastomycosis

A

Uveitis, panophthalmitis, glaucoma, acute retinal detachment –> irreversible blindness

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17
Q

Skin form of Blastomycosis

A

Ulcerative or granulomatous dermatitis

  • usually found in animal with the pulmonary form, indicating extensive dissemination and poor prognosis
  • granulomatous nodules and draining tracts
  • greasy exudate and matted hairs around ulcerated skin
  • common on: face, nose, lips, limbs, feet, pads and toes
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18
Q

Bone form of Blastomycosis

A
  • lameness (single or multiple bones involved)
  • invades osseous tissue
  • concurrent lymphadenopathy of affected side
  • osteolytic lesions at ends of long bones
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19
Q

Genitourinary form of Blastomycosis

A

Found in prostatic washes

  • signs associated with prostatitis
  • hematuria, pyuria
  • yeast leave in the urine
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20
Q

Best way to make a definitive diagnosis of any fungal disease?

A

Demonstrate the organism and associate it to the lesions

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21
Q

Which fungal agent makes a capsule?

A

Cryptococcus neoformans

- narrow based budding yeast cells surrounded by polysaccharide capsule

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22
Q

Which agents exist in the GIT of birds and bats?

A
  • Candidiasis

- Cryptococcus neoformans

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23
Q

Which agents do not occur in the GIT of birds and bats?

A
  • Histoplasma capsulatum
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24
Q

What does Histoplasma capsulatum look like?

A
  • in vivo: small, nonencapsulated, intracellular yeast cells (only intracellular yeast!)
  • histopathology: will see 2-40 yeast cells within a single host cell = shrunken cytoplasm creating the appearance of a capsule
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25
Q

What are the geographic areas for dimorphic fungi?

A
  • blastomycosis: MS and Ohio river basins, central Atlantic states
  • histoplasmosis: worldwide, eastern US, MS river valley basin, great lakes, Northeast
  • coccidiomycosis: limited to southwestern states
  • sporotrichosis: worldwide, common in tropics and in the South
26
Q

What is the defining feature of zygomycetes?

A

Coenoctic hyphae

  • gametangia –> zygospore
  • small heads (sporangia) near the edge of colongies
27
Q

Which agents do mycotic placentitis?

A
  • zygomycetes: cows caused by Mucor and Mortierella
  • candidia
  • aspergillosis
28
Q

Order Mucorales disease

A
  • mycotic ruminitis: calves (Absidia, Rhizopus, Mucor, Rhizomucor)
  • mycotic placentitis: cows (Mucor and Mortierella)
29
Q

Order Entomophthorales disease

A
  • Conidiobolus coronatus: mucocutaneous sites = sinusitis, nasopharyngitis, URI in horse
  • Basidiobolus ranarum: subq mycosis of the trunk and extremities in cattle and horses
30
Q

Which agents are sensitive to cycloheximide?

A

Zygomycetes
- cannot be cultured on Mycosel agar or SDA with C&C
Cryptococcus neoformans

31
Q

What is cycloheximide?

A

Added to agar to inhibit growth of saprophytic fungi

32
Q

Where do agents exist in their reservoir form?

A
  • dermatophytes: soil
  • pythium: water
  • zygomycetes: environmental saprophytes, laboratory contaminants
  • cryptococcus: soil, dried pigeon droppings
  • C. albicans: normal flora
  • Malassezia: normal human flora and animal cutaneous commensal flora
  • blastomyces: soil saphrophyte
  • histoplasmosis: soil (moist, feces of birds), decomposing trees
  • coccidiomycosis: soil (high temp, low humidity), around rodent burrows
  • sporotrichosis: soil, wood. vegetation
33
Q

What diagnostic test is run on Cryptococcus neoformans?

A
  • direct smear with India ink
  • culture on blood agar or SDA
  • immunodiagnosis via direct agglutination of circulating capsular antigens in a latex bead test
34
Q

Zoophilic dermatophytes

A

M. canis

- animals as their host and reservoir

35
Q

Geophilic dermatophytes

A

M. gypseum, T. mentagrophytes

- soil as their reservoir

36
Q

Anthropophilic

A

Fungus only found on humans, not animals!

- ex: Epidermophyton flocculosum

37
Q

What 3 species of dermatophytes cause 99.9% of ringworm in dogs and cats?

A
  • M. canis: 90% cats, 70% dogs
  • M. gypseum: 20%
  • T. mentagrophytes: 10%
38
Q

Which animals amplify Sporotrichosis, so that when it is introduced back into the environment, it causes zoonosis?

A

Cats

39
Q

What tissue is invaded with Dermatophytes and how far down does it go into the hair follicle?

A

Hair and skin

  • only non-viable keratinous tissue is invaded!
  • are non-invasive, do not survive in living tissues
  • grow down anagen hair shaft to Adamson’s fringe –> where hair shaft exits the follicle
40
Q

What dye’s are used to stain fungi?

A
  • 10% KOH: used to clear host cells
  • PAS: specific for all fungi –> hyphae stain bright red
  • India ink
41
Q

Do you culture dimorphs?

A

No!

  • biosafety level 3 (same as anthrax)
  • sporotrichosis: definitive diagnosis requires culture and demonstration of both phases*
42
Q

What are the dimorphic fungi?

A
  • Blastomyces dermatitidis
  • Histoplasma capsulatum
  • Coccidioides immitis
  • Sporothrix schenckii
43
Q

Which agents cause nasopharyngitis in horses?

A

Aspergillosis: gutteral pouch infection

**Conidiobolus coronatus: infects mucocutaneous sites = sinusitis, nasopharyngitis, upper respiratory disease in horses

44
Q

What is the infectious particle of pythium?

A

Zoospore

45
Q

What is the pathogenesis of pythium?

A

Zoospore contacts mucosa of GIT –> attach to damaged tissue, or invade mucosa and lymphatics
- OR: superficial injury in cattle, dogs, horses allows zoospore attachment, invasion and germination
= granulomatous inflammatory response

46
Q

Pythium in the dog

A

Emaciation, vomiting, diarrhea, anorexia

  • firm abdominal mass is palpated
  • thickened stomach wall
47
Q

Pythium in the horse

A

Granulomatous lesions, fistulated, ulcerated

- yellow-gray necrotic masses or cores of tissue (kunkers)

48
Q

Pythium in calves

A

Multifocal areas of dermal thickening and ulceration on extremities

49
Q

What is a kunker made out of?

A

Eosinophilic coagulum containing inflammatory cells with pyknotic nuclei

50
Q

Overall histopathology of Pythium

A

Initially acute exudative inflammation
- characterized by predominant eosinophilia and early focal necrosis –> development of chronic inflammatory, and granulomatous reaction –> sequestration of necrotic areas

51
Q

Which fungus gets in the eyes?

A
  • Aspergillosis fumigatus (horse eye)

- ocular form of Blastomyces dermatitidis

52
Q

What fungal agent causes brooder pneumonia in chickens?

A

Aspergillosis

53
Q

Allylamines and non-azole ergosterol biosynthesis inhibitors

A

Lead to reduced ergosterol biosynthesis

  • conceptually related to azole antifungal agents
  • ex: terbinafine: inhibits squalene epoxidase
54
Q

Antimetabolites

A

DNA substrate analog that leads to incorrect DNA synthesis

  • flucytosine
  • synergistic with azoles and amphotericin B
55
Q

Azoles

A

Largest group, all inhibit synthesis of ergosterol by blocking the action of 14-alpha-demethylase
- ex: fluconazole

56
Q

Glucan synthesis inhibitors

A

Inhibit glucan synthesis

  • not used in vet med, too expensive
  • inhibition of glucan produces significant antifungal effects
  • ex: caspofungin
57
Q

Polyenes

A

Potent, act by binding to fungal cell membrane using ergosterol as a target –> fungus leaks electrolytes
- ex: Amphotericin B (highly nephrotoxic!!)

58
Q

Miscellaneous systemic agents

A

Griseofulvin: disrupts mitotic spindle

  • used against dermatophytes
  • comes as powder, mix in oil to help with absorption
59
Q

Is Pythium a fungus?

A

Is more closely related to red algae and diatoms

  • contains cellulose and beta-glucan in its cell wall as opposed to chitin, chitosan, alpha/beta glucans, and alpha mannans
  • does NOT contain ergosterol!!
  • still dealt with my mycologists due to morphology and staining characteristics
60
Q

How is Pythium treated?

A

Typical antifungal/chemotherapeutic agents do not work

  • surgical removal of affected tissue is treatment of choice (often not all affected tissue is removed)
  • experimental bacterin used in horses and dogs at LSU, Australia
61
Q

What fungus is a concern in piglets?

A

Candidia

- pseudomembrane on the tongue, esophagus, and stomach = vomiting and rapid wasting

Infectious Agents 2 (29 decks)

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