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MOD II Exam II > Fungi > Flashcards

Fungi Flashcards

1
Q

Geographic distribution in midwest and central US along Mississippi and Ohio river valleys

A

Histoplasma capsulatum

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2
Q

Transmission and pathogenesis of histoplasma capsulatum

A

Exposure to bird or bat droppings

Spores in droppings are inhaled then ingested by macrophages

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3
Q

Diagnosis of Histoplasma capsulatum

A

Histologically presents with macrophages containing intracellular oval bodies with KOH prep

Note that histoplasma is smaller than RBCs — macrophages contain many of these oval bodies

Could also use serum or urine Ag test

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4
Q

Clinical presentation of Histoplasma in healthy vs. immunocompromised individuals

A

Healthy usually asymptomatic but can present with pneumonia and granuloma formation that may calcify and mimic Tb infection. May also see erythema nodosum - painful red lesions on shins

In immunocompromised may lead to HSM because it targets reticuloendothelial system macrophages and there are many in liver and spleen (this is disseminated infection)

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5
Q

The systemic mycoses are considered dimorphic. What are the systemic mycoses?

A

Histoplasma capsulatum
Blastomyces dermatidis
Coccidoides immitis
Paracoccidioides brasiliensis

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6
Q

The systemic mycoses are considered dimorphic. What does this mean? What is the exception?

A

Dimorphic - exists in 2 forms based on environment. “Mold in the cold (external, soil), Yeast in the heat (body/lungs)”

Exception is Coccidioides immitis which dimorphic. It exists as a mold in the cold but forms spherules filled with endospores in the lungs

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7
Q

Geographic distribution in Great Lakes and Ohio river valley

A

Blastomyces dermatidis

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8
Q

Transmission and pathogenesis of blastomyces dermatidis

A

Inhalation of aerosolized spores —> replication by broad based budding (seen on KOH prep)

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9
Q

Dx and clinical features of blastomycoses infection

A

Broad-based budding yeast seen on KOH prep

Yeasts are same size as RBCs on blood smear; can also be dx by urine Ag test

CXR shows patchy alveolar infiltrate

Most are asymptomatic but may see disseminated infxn in immunocompromised, which affects skin and bone (osteomyelitis)

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10
Q

Geographic distribution in California and Southwestern US

A

Coccidioides immitis

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11
Q

How does one usually come into contact with coccidioides immitis? What events tend to increase incidence in endemic regions?

A

Inhalation of spores in dust

Dust storms and/or earthquakes cause increase in incidence

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12
Q

Coccidioides mycoses can cause systemic infections; they are dimorphic organisms that exist as mold in the cold and form spherules filled with endospores in the lungs of humans. How do these spherules compare to RBCs under the microscope?

A

Spherules are larger than RBCs

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13
Q

Clinical features of Coccidioides immitis in healthy people

A

Usually asymptomatic in healthy people but can cause self-limiting PNA with fever, cough, and arthralgia

CXR may show nothing, or cavities and/or nodules

Can also see erythema nodosum (note that this is more common in coccidioides than histoplasma) - this represents robust immune response - so it is only really seen in healthy people

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14
Q

Clinical features of Coccidioides immitis in immunocompromised

A

Skin and lung manifestations

Dissemination to bone and meninges (meningitis)

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15
Q

Dx of coccidioides immitis

A

KOH, culture, or blood culture with IgM to coccidioides

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16
Q

Geographic distribution in South America (often Brazil)

A

Paracoccidioides brasiliensis

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17
Q

Characteristic features of Paracoccidioides brasiliensis

A

Dimorphic

Yeast form looks like “captains wheel” in lungs, and is larger than RBC

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18
Q

Pathogenesis and clinical features of Paracoccidioides brasiliensis

A

Inhalation —> dissemination —> LAD —> spread to lungs causing granulomas; also see mucocutaneous lesions - often in mouth

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19
Q

What are the cutaneous mycoses?

A

Malassezia furfur

Dermatophytes (epidermophytan, trichophytan, microsporum)

Sporothrix schenckii

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20
Q

What primary condition is caused by Malassezia furfur?

where does this organism thrive?

A

Pityriasis versicolor = hyper and/or hypopigmented patches on skin

Organism thrives in hot and humid conditions

21
Q

Describe appearance of Malassezia furfur on KOH prep of skin scrapings

What layer of the skin is typically affected?

A

“Spaghetti and meatball” appearance

Typically remains confined to stratum corneum layer of epithelium

22
Q

MOA of Malassezia furfur

A

Produces melanocyte damaging acids via lipid degradation

23
Q

Malassezia furfur typically remains confined to the skin except in what patient population?

A

May cause disseminated infection in neonates on total parenteral nutrition (TPN) causing thrombocytopenia and sepsis

24
Q

Clinical manifestations of dermatophytes (epidermophytan, trichophytan, microsporum)

A

Tinea rashes (“ring-worm”) = pruritic!

Tinea capitis affects the head

Tinea corporis affects the body

Tinea cruris = jock itch

Tinea pedis = athletes foot

can also cause onychomycosis = infection of the nails

25
Q

Dermatophytes often affect athletes, or they can come from animals like dogs. How are these infections diagnosed?

A

Typically based on H&P

Can see hyphae on KOH prep

Woods lamp used to diagnose microsporum

26
Q

Rose-gardener’s disease often transmitted by scratches from rose bush or other physical trauma with dimorphic branching hyphae at 25 C

A

Sporotrichosis - caused by Sporothrix schenckii

27
Q

Diagnosis and clinical features of sporotrichosis (sporothrix schenckii)

A

Dx by culture (gold standard) OR biopsy showing granulomas OR microscopy showing cigar shaped budding yeasts

Clinical presentation: ulcer at the site of initial trauma —> ascending infection via lymphatics

28
Q

Describe the dimorphic character of candida albicans

A

Dimorphic with pseudohyphae (yeast) at 20 C, and germ-tube hyphae (mold) at 37 C

[so it is opposite the usual dimorphic pattern — this is yeast in the cold and mold in the heat!]

29
Q

What about candida albicans makes it a risk for patients with CGD?

A

It is catalase+

30
Q

Candida albicans is part of the normal flora in most people, and does not typically cause infection in healthy individuals. What are some clinical findings when it does cause infection?

A

Diaper rash in characteristic pattern d/t heat and humidity in diaper region

Oral candidiasis in immunocompromised or oral steroid users

Candidal esophagitis (AIDS-defining illness with CD4<100)

Vaginal candidiasis

Candidal endocarditis (IV drug users, commonly affects tricuspid)

31
Q

What patient populations have increased risk of candidal vulvovaginitis?

How is vaginal candidiasis differentiated from gardnerella infection?

A

Increased risk in diabetics and women taking oral contraceptives

differentiated from gardnerella because candida does NOT alter vaginal pH

32
Q

Besides candida albicans, what other fungus is catalase+?

A

Aspergillus fumigatus

33
Q

How is aspergillus associated with hepatocellular carcinoma?

A

Peanuts and grain crops are associated with aflatoxins produced by aspergillus flavus; these aflatoxins are carcinogenic for hepatocellular carcinoma

34
Q

Describe the morphology of aspergillus flavus and how this differs from mucor

A

Acute angle branching+septations; forms conidiophores with fruiting bodies

Mucor does not septate and has wide-angle (90 degree) branching compared to aspergillus

35
Q

Transmission of aspergillus fumigatus occurs via inhalation. What are the 3 disease manifestations?

A
  1. Allergic bronchopulmonary aspergillosus (ABPA)
  2. Aspergillomas
  3. Angioinvasive aspergillosis
36
Q

Describe allergic bronchopulmonary aspergillosis (ABPA)

A

Type 1 HSR with wheezing, fever, and migratory pulmonary infiltrate

Blood work shows increased IgE

37
Q

Describe aspergillomas caused by aspergillus fumigatus infxn

A

Forms balls of fungus in lungs that are gravity dependent, so they show up at the bottom of a CXR

Formation of these fungal lesions is associated with prior Tb infection which created cavities

38
Q

Describe angioinvasive aspergillosis

A

Occurs in immunocompromised, particularly in leukemia and lymphoma pts

Aspergillus invades blood vessels and disseminates through the body, leading to kidney failure, endocarditis, and ring-enhancing lesions in the brain on CT

It can also spread to the paranasal sinuses, causing necrosis around the nose (this also occurs in mucor so it is not diagnostic of aspergillus!)

39
Q

Describe morphology of cryptococcus neoformans and where it is found

A

Heavily encapsulated (contains repeating polysaccharide capsular Ags) as main virulence factor — antiphagocytic

Urease+

Found in soil and pigeon droppings

40
Q

Clinical features of cryptococcus neoformans infection

A

Opportunistic infection often affecting HIV pts

Causes cryptococcal pneumonia with fever, cough, and dyspnea (or may be asymptomatic)

Can also spread to the meninges, and is the MCC of fungal meningitis

41
Q

What characteristics are indicative of cryptococcus neoformans infection on imaging in someone with cryptococcal meningitis?

A

“Soap bubble” lesions in gray matter of brain

42
Q

Besides imaging, how is a cryptococcal neoformans infection diagnosed?

A

Bronchopulmonary washing then stained with red or silver

Lumbar puncture + India Ink stain showing 1-10 micrometers of yeast with “halos”

Latex aggluttination test detects repeating polysaccharide Ag —> agglutination is + testq

43
Q

What fungi are associatiated with opportunistic fungal infections?

A 
Candida albicans
Aspergillus fumigatus
Cryptococcus neoformans
Mucormycetes
Pneumocystis jiroveci
44
Q

What patients are at high risk for mucormycetes (mucor spp, rhizopus spp.) infections?

A

Immunocompromised (often those with leukemia, neutropenia)

Diabetics (most common predisposing factor is DKA)

45
Q

What is rhizopus?

A

Bread mold; Type of mucormycetes

46
Q

Describe morphology of mucormycetes and how it is different from aspergillus

A

Hyphae are non-septate and wide-angle branching (~90 degrees)

[aspergillus are septated and acute angle branching]

47
Q

Pathogenesis of Mucor infection

A

Spore inhalation —> proliferation in blood vessels —> invasion through cribriform plate —> necrosis of tissues

Tissue necrosis eventually leads to rhinocerebromucomycoses and frontal cortex abscesses

Black eschar forms on face and nasal cavity, indicated deep penetration into brain which may manifest as neurodisturbances and death

48
Q

Transmission and clinical features of pneumocystis jiroveci

A

Respiratory transmission

Asymptomatic in healthy people

In immunocompromised — Diffuse interstitial pneumonia with NON-productive cough and NO lung consolidations on CXR. However, may see “ground glass” or “crushed ping pong ball” appearance on CXR

49
Q

If pneumocystis pneumonia is suspected based on “ground glass” appearance on chest X-ray, how would you confirm the dx?

A

Bronchoalveolar lavage (BAL) then stain wtih methamine silver stain — will see ovoid/disc-shaped yeast

Could also do lung biopsy but that is more invasive

MOD II Exam II (7 decks)

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