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Microbiology/Immunology > Fungi 2 > Flashcards

Fungi 2 Flashcards

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1
Q

Fungal Molds vs Yeasts

A
  • Molds:
  • asexual or sexual reproduction with spores
  • multicellular: not very mobile in the body

Yeasts:

  • asexual by budding
  • single celled: can circulate resistant to phagocytosis

Other:
-dimorphs- thermal dimorphs

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2
Q

Four categories of Fungal Infections (Mycosis)

A
  • Superficial mycoses- minor infections or overgrowth on skin surface
  • Subcutaneous mycoses- granulomatous infection of lower dermal layers, slow spread from periphery toward trunk
  • Systemic mycoses- potentially-dangerous infection spreading from inhaled spores
  • Opportunistic mycoses- cause a variety of disease predicted on the patents’ preexisting conditions
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3
Q

Themes of Superficial Mycoses

A
  • caused by fungal growth on superficial skin layer
  • does not require thermal dimorphism: often growing on cool exterior as hyphae
  • very common, but symptoms are minor: itch or discoloration
  • treated with topical azoles, alt oral griseofulvin
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4
Q

Superficial Mycoses: Dermatophytosis

A
  • caused by dermatophytes
  • infect only superficial keratinized structures- skin, hair, nails
  • produce keratinases that allow invasion of cornified cell layer
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5
Q

Pathogenesis of Dermatophytosis

A

-form chronic infections in warm, humid areas in on body surface
-inflamed circular border of papules and/or vesicles, broken hairs, thickened, broken nails
-skin within border may be normal
-named for affected body part:
tinea capitis- head
tinea corporis- ringworm
tinea cruris- Jock itch
tinea pedis- Athletes’s foot
-transmitted by fomites or by autoinoculation form other sites on body

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6
Q

Hypersensitive dermatophytid reactions

A
  • vesicles on fingers
  • caused by hypersensitivity to circulating fungal antigen
  • vesicles do not contain live fungus or spores
  • tinea is very common: accounts for 10-20% of visits to US dermatologists
  • no morbidity results from the primary infection, but prolonged itch can lead to bacterial superinfection
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7
Q

Diagnosis of Dermatophytosis

A
  • exam: itching, redness, history of tight or wet clothing
  • microscopic exam: scraping from affected skin or nail, treat with 10% KOH, exame for hyphae and spores
  • culture on Sabouraund’s agar at room temp
  • may show fluorescence when examined under Wood’s lamp
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8
Q

Dermatophytosis: Treatment and Prevention

A
  • topical antifungal treatment: Terbinafine (Lamisil), Undecylenic acid (Desenex), Miconazole (Micatin), Tolnaftate (Tinactin)
  • treat all affected body sites simultaneously

alternate: oral griseofulvin (Fulvicin)
- keep skin dry and cool

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9
Q

Themes in Subcutaneous Mycoses

A
  • introduced by trauma exposing subcutaneous tissue to soil or vegetation
  • slow spread from trauma site toward trunk by lymphatics
  • thermal dimorphism
  • patient presents with history of ineffective antibiotic treatment
  • treated with oral azoles
  • in serious cases, may begin with short course of amphoterin B and surgery
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10
Q

Sporotrichosis

A
  • Sporothrix schenckii and other species
  • thermally dimorphic
  • found on vegetation
  • often seen in gardeners, particularly of roses (thorns)
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11
Q

Pathogenesis of Sporotrichosis

A
  • introduced into skin by thorn puncture
  • yeasts grow at site and form painless pustule or ulcer
  • draining lymphatics form suppurating subcutaneous nodules
  • symptoms wax and wane over years
  • may progress to disseminated disease and meningitis if immunosuppressed
  • patients with COPD and long term corticosteriod may develop pulmonary symptoms from inhaling the spores; difficult to distinguish from TB or histoplasmosis
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12
Q

Exam of Sporotrichosis

A
  • painless pustule or ulcer on hand or arm: reddish, necrotic, nodular papules may extend along lymphatic from initial injury site
  • history of gardening, farming, landscaping, berry-picking
  • history of ineffective antibiotic treatment
  • in AIDS, may see nodules disseminated over whole body
  • in COPD+ alcoholism, respiratory distress
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13
Q

Diagnostic Lab of Sporotrichosis

A
  • tissue biopsy: round or cigar shaped budding yeasts- hard to see
  • culture at room temp from pus, biopsy: hyphae with oval conidia in clusters at tip of slender conidiophores (resembles a daisy)
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14
Q

Treatment and Prevention of Sporotrichosis

A
  • treatment: 3-6 months itraconazole or other oral azoles for normal form of disease
  • for more serious types, admit for Amphotericin B
  • prevention: garden gloves
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15
Q

Recurring Themes of Systemic Mycoses

A
  • environmental: spores/fungi in soil
  • inhaled into lungs
  • thermal dimorphism
  • wide range of severity: asymptomatic clearance to death
  • not person to person transmissible
  • coccidioides/histoplasma/blastomyces: mimic TB
  • History: American dirt, not foreign crowds
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16
Q

Coccidioides

A
  • coccidioides= coccidioidomycosis
  • coccidioides immitis and C. posadasii
  • dimorphic: mold in soil, spherule in tissue
  • grow in the rainy season as mycelial (noninfectious)
  • in the dry summer, forms hyphae with alternating arthrospores and empty cells
  • when disturbed by wind or excavation, readily release arthroconidia (infectious)
  • spores are carried by wind, inhaled by humans
  • endemic in southwest US and Latin America; may travel home in returning patient or arrive in contaminated shipped material
  • caseload has spiked in this century as endemic areas have become geriatric population centers: Phoenix, Tucson, Fresno, El Paso
  • symptomatic disease can keep a previously healthy person out of school or work for a month
  • 80% of residents in endemic areas develop positive skin test within 5 years
17
Q

Pathogenesis of Coccidioides

A
  • arthrospores are inhaled: infectious dose can be as low as 1U, though high dosage is more likely to cause symptoms
  • within terminal bronchiole change form:
  • spherules: highly resistant to eradication by immune system
  • 30um diameter
  • thick, doubley refractive wall
  • filled with endospores
  • wall ruptures to release endospores, develop into new spherules
  • spherules and endospores are not infectious
  • depends a lot of exposure and healthy or immunosuppressed
18
Q

Phases of Coccidioides Pathogenesis

A
  • Acute phase- innate immunity (macrophage response) attempts to clear infection: often successful
  • Chronic phase: innate immunity inadequate for clearance; lymphocytes and histiocytes initiate granuloma and giant cell formation (containmnet)
  • if CMI is healthy, infection is contained in granulomas in lung; many eventually cleared asymptomattically
  • many patients who become ill have nonspecific flulike symptoms that resolve at home (~60% exposures = asymptomatic and flulike
19
Q

Valley fever

A
  • coccidioides symptomatic disease may appear as Valley Fever or desert rheumatism
  • fever
  • arthralgias
  • erythema nodosum
  • erythema multiform
  • chest pain
20
Q

Risk factors for cocidioides

A
  • if immunosuppressed, disseminated infection both by intracellular travel in macrophages and hematogenous spread
  • risk factors: advanced age, immunocompromised, late-stage pregnancy, occupational high-level exposure ( farmers, construction workers, archeaologists), black or Filipino race
  • may affect any organ; primary seen in bone and meninges
  • induced immune anergy; may be rapidly fatal
21
Q

Coccidioides Lab Diagnosis

A
  • take biopsies of relevant tissues, CSF, blood, urine, stain with H and E or funal stains; examine microscopically for spherules
  • cultures on Sabourand’s agar at 25C: cottony white mold composed of hyphae with arthrospores: cultures are infectious! Handle in Biosafety 3
  • Serology for exposure, titers: IgG from blood and/or CSF titer spikes if disseminating. Positives are very reliable, but some false negatives occur
22
Q

Treatment of Coccidioides

A
  • high morbidity but low mortality
  • no treatment required for mild disease
  • must treat is predisposed to complications: severe immunosuppression, diabetes, cardiopulmonary disease, (oral azoles), pregnancy ( Amphotericin B)
  • persisiting lung lesions or disseminated: Amphotericin B and long term itraconazole
  • minimum of 6 months drug therapy, follow ups for at least a year
23
Q

Opportunistic Mycoses Themes

A
  • diseases and severity are widely varied, depending on the patients’ pre-existing conditions
  • optimal treatment addresses both the infection and the underlying problem
24
Q

Crytococcosis

A

-crytococcus neoforms and C. gattii form 5 serotypes, A,D, and AD are neoforms, B and C are gattii

  • crytococcosis, esp cryptococcal meningitis
  • C. neoformans is environmental, found worldwide in soil contaminated w/ bird droppings, esp pigeon

-oval yeasts with narrow based buds and wide polysaccharide capsule

  • pathogenic strains grow at 37C
  • not thermally dimorphic
  • no human to human transmission
  • polysaccharide capsule
  • disseminated disease fatal before Amphotericin B
25
Q

Crytococcosis Pathogensis

A
  • transmitted by inhalation: pigeon droppings may be contagious for years
  • lung infection may be asymptomatic or lead to pneumonia
  • can be intracellular infection in alveolar macrophages
  • immunocompentent hosts restrict infection to lungs
  • successful hosts raises Helper Ts, skin test conversion, antibodies to capsule
  • deficient CMI, esp AIDs predisposing for dissemination
  • dissemination- crytococcal meningitis w/ skin nodules

Virulence factors: capsule, melanin in cell wall (antiphagocytic), Phospholipase B for invading tissue

26
Q

Diagnosis of Cryptococcosis

A

History: steriod use, malignant disease, transplantation, HIV
Skin: biopsy
Pulmonary: range from symptomatic to ARDS, cough and chest pain common
with HIV: fever, cough, headache, weight loss, positive cultures in blood, CSF, urine
CNS: subacute meningitis, antifungal needed to live

27
Q

Lab for Cryptococcosis

A
  • CSF: stain with India ink to observe yeast with wide capsule
  • Biopsy: stain with methenamine silver, periodic acid-Schiff, mucicarmine
  • Culture: at 37C for CSF, blood, urine, sputum for mucoid colonies on Sabourand agar, will produce melanin in culture on special media
  • Serology: crag for crytococcal antigen in blood and CSF
  • Routine bloodwork may be normal
28
Q

Treatment of Cryptococcosis

A
  • pulmonary cryptococcosis may not need treatment
  • Amphotericin B plus flucytosine if meningitis
  • In AIDS use fluconazole for long term suppression
  • examine CSF weekly

Microbiology/Immunology (46 decks)

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