questions 5

Opportunistic Mycoses

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Topic updated on 04/09/14 2:58pm

Candida albicans
  • Diseases
    • in normal hosts
      • oral thrush
      • candida intertrigo (skin folds)
      • vaginitis
      • diaper rash
      • perleche (angular cheilitis)
        • cracks at the corner of the mouth
        • seen in malnutrition
    • in immunocompromised (especially AIDS or neutropenic)
      • esophagitis
        • thrush spreads down GI tract
      • endocarditis
        • in IV drug users
      • septicemia
        • due to indwelling catheters (e.g. subclavian catheter)
      • disseminated candidiasis
      • chronic mucocutaneous candidiasis
      • local infection is due to T-cell deficiency while systemic infection is due to neutropenia
  • Pathogenesis
    • normal flora → opportunistic infection
  • Laboratory
    • yeast with pseudohyphae and budding at 20°C
    • germ tube formation at 37°C (diagnostic)
      • true hyphae sprout from yeast and are seen on light microscopy
  • Treatment
    • Nystatin for superficial infection
    • Amphotericin B for systemic infection
Cryptococcus neoformans
  • Diseases
    • meningitis
      • in AIDS (most common meningitis)
      • in Hodgkins disease (most common meningitis)
      • "soap bubble" lesions in brain
      • can also cause encephalitis
    • pneumonia
      • seen in pigeon breeders
    • skin and bone infections
  • Pathogenesis
    • transmitted via PIGEON DROPPINGS
    • yeast spreads hematogenously to brain
    • 75% of cases in immunocompromised
  • Laboratory
    • polysaccharide capsule
      • wide capsular halo can be seen
      • the only pathogenic fungus with a polysaccharide capsule
    • unequal budding with narrow base
    • monomorphic
    • culture on Sabouraud's agar
      • urease positive yeast
    • stains with India ink
    • mucicarmine stains red
    • methenamine silver (GMS) is also used
    • latex agglutination test 
      • detect polysaccharide capsular antigen in CSF
  • Treatment
    • amphotericin B + flucytosine 10 weeks
    • followed by fluconazole
Aspergillus
  • Diseases, Pathogenesis, and Treatment
    • inhalation of ubiquitous Apergillus spores causes 3 diseases
    • allergic bronchopulmonary aspergillosis
      • asthma-like allergic reaction in airways
        • proximal bronchiectasis
      • type I and type IV hypersensitivity reactions
      • mucus plugs form but do not penetrate tissue
      • treatment
        • systemic corticosteroids and oral itraconazole
    • aspergilloma
      • seen in TB patients (or other granulomatous disease)
      • "fungus ball" forms in pre-existing lung cavities
      • treatment
        • surgery
    • invasive aspergillosis
      • invasive infection of the lung
      • usually in immunocompromised
      • pleuritic pain, hemoptysis
      • infiltrate seen on X-ray and CT
      • treat with strongest antifungals including
        • voriconazole, amphotericin B, or caspofungin
  • Toxins
    • Aspergillus produces aflatoxin
      • causes liver damage and liver cancer
        • aflatoxin B1 causes G:C -> T:A mutation in codon 249 of p53 
        • increased risk of hepatocellular carcinoma
  • Laboratory
    • monomorphic
    • septate hyphae branch at acute angles 
      • "ASpergillus is Acute and Septate"
    • fruiting bodies are rare
    • a recycler (found in compost piles)
    • catalase-positive
Mucor, Rhizopus
  • Diseases
    • rhinocerebral infection (mucormycosis)
      • frontal lobe abscesses
      • paranasal swelling
      • hemorrhage from nose and eyes
    • fungi also penetrate blood vessel walls
      • results in infarction and necrosis
  • Pathogenesis
    • spores found in soil
    • fungus penetrates through sinuses into brain
    • seen in acidotic patients
      • diabetic ketoacidosis
      • leukemia
  • Laboratory
    • irregular non-septate hyphae branch at wide angles
    • filamentous
  • Treatment
    • amphotericin B (must act quickly)
    • surgical debridement
Pneumocystis jiroveci
  • Formerly called P. carinii
  • Diseases
    • "PCP" ("P. carinii" pneumonia)
      • diffuse interstitial pneumonia
        • fever
        • cough, shortness of breath
      • patchy infiltrate with "ground glass" appearance bilaterally on chest X-ray
      • seen in immunosuppressed
        • especially AIDS
          • especially CD4 < 200
        • malnourished or premature babies
  • Pathogenesis
    • inhaled
    • kills Type I pneumocytes
    • Type II pneumocytes overreplicate and damage alveolar epithelium
    • fluid leaks into alveoli producing an exudate
      • seen as honeycomb appearance on H&E
  • Laboratory
    • a yeast (originally classified as protozoan)
    • obligate extracellular parasite
    • diagnose with
      • lung biopsy or lavage
      • methenamine silver stained cysts seen in tissues
  • Treatment
    • TMP-SMX
    • if sulfa allergy
      • atovaquone
      • pentamidine
      • dapsone
  • Prophylaxis
    • treated prophylactically in HIV patients with CD4 < 200


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Qbank (4 Questions)

TAG
0) (M1.MC.14) A 31-year-old female undergoing treatment for leukemia is found to have a frontal lobe abscess accompanied by paranasal swelling. She additionally complains of headache, facial pain, and nasal discharge. Biopsy of the infected tissue would most likely reveal which of the following? Topic Review Topic

1. Yeast with pseudohyphae
2. Budding yeast with a narrow base
3. Septate hyphae
4. Irregular non-septate hyphae
5. Spherules containing endospores

PREFERRED RESPONSE ▶
TAG
0) (M1.MC.34) A 43-year-old HIV positive male presents with signs and symptoms concerning for a fungal infection. He is currently not on antiretrovirals and his CD4 count is 220. Which of the following candidal infections could be seen in this patient but would be very rare in an immunocompetant host? Topic Review Topic

1. Oral thrush
2. Vaginitis
3. Intertrigo
4. Esophagitis
5. Endocarditis

PREFERRED RESPONSE ▶
TAG
0) (M1.MC.111) A 41-year-old HIV-positive male presents to the ER with a 4-day history of headaches and nuchal rigidity. A lumbar puncture shows an increase in CSF protein and a decrease in CSF glucose. When stained with India ink, light microscopy of the patient’s CSF reveals encapsulated yeast with narrow-based buds. Assuming a single pathogenic organism is responsible for this patient’s symptoms, which of the following diagnostic test results would also be expected in this patient? Topic Review Topic

1. Cotton-wool spots on funduscopic exam
2. Ring-enhancing lesions on CT imaging
3. Latex agglutination of CSF
4. Acid-fast cysts in stool
5. Frontotemporal atrophy on MRI

PREFERRED RESPONSE ▶
TAG
0) (M1.MC.188) A 50-year-old HIV-positive male presents to the ER with a two-day history of fever and hemoptysis. Chest radiograph shows a fibrocavitary lesion in the right middle lobe. Biopsy of the afflicted area demonstrates septate hyphae that branch at acute angles. Which of the following is the most likely causal organism? Topic Review Topic

1. Mycobacterium tuberculosis
2. Candida albicans
3. Pneumocystis jeroveci
4. Aspergillus fumigatus
5. Naegleria fowleri

PREFERRED RESPONSE ▶


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