Environmental sources and prevention

Environmental sources and prevention

Environmental sources and prevention

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Histoplasma capsulatum - Bat Cave Blues

  • Environmental Source: Soil contaminated with bird or bat droppings (guano).
    • Common in caves, chicken coops, and starling roosts.
    • Endemic to the Mississippi and Ohio River valleys.
  • Transmission & Prevention:
    • Inhalation of airborne microconidia (spores) from disturbed soil.
    • Prevention: Wear respiratory protection (e.g., N95 mask) in high-risk environments like caves (spelunking) or when cleaning chicken coops.

Histoplasma yeast forms are found intracellularly within macrophages and are notably smaller than red blood cells.

📌 Mnemonic: "Histo Hides" inside macrophages. Cave diving or exploring chicken coops gives you "Bat Cave Blues".

Blastomyces & Coccidioides - Dusty Deserts & Decaying Debris

Global endemic areas of dimorphic fungal infections

  • Blastomyces dermatitidis

    • Source: Decaying organic matter (wood, leaves) and moist, acidic soil.
    • Geography: Eastern & Central US, especially the Ohio & Mississippi River Valleys and Great Lakes region.
    • Transmission: Inhalation of airborne conidia after soil disruption (e.g., excavation, farming).
  • Coccidioides immitis/posadasii

    • Source: Alkaline, sandy soils in arid climates.
    • Geography: Southwestern US (Arizona, California), Northern Mexico. 📌 "Valley Fever".
    • Transmission: Inhalation of arthroconidia stirred by wind, earthquakes, or construction.
    • Prevention: High-risk individuals should wear N95 masks in endemic areas and avoid dust exposure.

⭐ Coccidioides is highly virulent; inhalation of just a single arthrospore can cause infection, making it a significant laboratory biohazard.

Sporothrix & Paracoccidioides - Thorny Gardens & Tropic Wheels

  • Sporothrix schenckii ("Rose Gardener's Disease")

    • Source: Found in soil, sphagnum moss, and on rose thorns.
    • Transmission: Traumatic inoculation of skin (e.g., thorn prick).
    • Prevention: Wear protective gloves and clothing when gardening or handling hay/moss.
    • 📌 Mnemonic: Think of a gardener who "plants a rose in a pot" (Sporothrix).
  • Paracoccidioides brasiliensis

    • Source: Endemic to soil and vegetation in rural Latin America, especially Brazil.
    • Transmission: Inhalation of airborne conidia.
    • Prevention: Difficult due to airborne nature; minimize dust exposure in endemic regions.

Lymphocutaneous sporotrichosis with lymphatic spread

Exam Favorite: Sporothrix classically presents as lymphocutaneous sporotrichosis, where a primary pustule or ulcer forms at the inoculation site, followed by a chain of subcutaneous nodules ascending along the lymphatic channels.

Prevention & Prophylaxis - Fungal Forcefield

  • Primary Prevention: Reduce exposure in endemic regions.
    • Avoid activities like cleaning chicken coops, exploring caves (Histoplasma), or disturbing soil/decaying wood (Blastomyces).
    • Use respiratory protection (e.g., N95 masks) during high-risk activities.

Person in PPE with respirator for fungal spore prevention

  • Chemoprophylaxis: Generally not recommended for healthy individuals.
    • Considered for specific high-risk, immunocompromised patients (e.g., severe immunosuppression, post-transplant) in hyperendemic areas.
    • Primary agent: Itraconazole.

High-Yield: Prophylaxis with itraconazole is indicated for HIV patients with CD4 counts < 150 cells/µL in areas where Histoplasma capsulatum is hyperendemic.

High‑Yield Points - ⚡ Biggest Takeaways

  • Histoplasma is found in bird and bat droppings; prevent with respiratory protection in endemic areas.
  • Blastomyces lives in moist soil and decaying wood, primarily in the Eastern/Central US.
  • Coccidioides thrives in the alkaline desert soil of the Southwestern US; prevent with dust control.
  • Sporothrix is associated with rose thorns and sphagnum moss (rose gardener's disease).
  • Most systemic infections are acquired via inhalation of spores, except for Sporothrix (traumatic inoculation).

Practice Questions: Environmental sources and prevention

Test your understanding with these related questions

A 26-year-old man comes to the physician for a follow-up examination. He was diagnosed with HIV infection 2 weeks ago. His CD4+ T-lymphocyte count is 162/mm3 (N ≥ 500). An interferon-gamma release assay is negative. Prophylactic treatment against which of the following pathogens is most appropriate at this time?

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Flashcards: Environmental sources and prevention

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Blastomycosis are _____ RBCs

TAP TO REVEAL ANSWER

Blastomycosis are _____ RBCs

the same size as (larger than/smaller than/the same size as)

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