Coccidioides immitis/posadasii

Coccidioides immitis/posadasii

Coccidioides immitis/posadasii

On this page

Coccidioides - The Valley Fever Villain

  • Epidemiology: Dimorphic fungus endemic to Southwestern US/Mexico. 📌 "Valley Fever."
  • Transmission: Inhalation of arthroconidia from disturbed soil/dust.
  • Pathology: Forms spherules packed with endospores in tissue (not yeast).
  • Clinical:
    • Most asymptomatic.
    • Acute pneumonia (flu-like illness).
    • Disseminated (immunocompromised): skin, bones, meningitis. Erythema nodosum is common.
  • Treatment: Fluconazole/itraconazole. Amphotericin B for severe/meningeal cases.

⭐ Spherules containing endospores seen on tissue biopsy are pathognomonic. They are significantly larger than RBCs.

Coccidioides immitis/posadasii spherules with endospores

Epidemiology - Desert Soil Dweller

Coccidioides endemic areas in the US

  • Geographic Hotspots: Endemic to arid regions of the Southwestern US (esp. Arizona, California's San Joaquin Valley), Northern Mexico, and South America.
  • Habitat: Lives in alkaline desert soil.
  • Transmission: Inhalation of airborne arthroconidia, especially after soil disruption.
    • Triggers: Dust storms, earthquakes, construction, and farming.

⭐ A major outbreak occurred after the 1994 Northridge earthquake in California, a classic example of environmental disruption leading to widespread infection.

Clinical Picture - The Great Imitator

  • ~60% Asymptomatic; most infections are subclinical.
  • Primary Pulmonary Disease ("Valley Fever"): 1-3 weeks post-exposure.
    • Mimics community-acquired pneumonia (CAP): fever, cough, pleuritic chest pain, fatigue.
    • Allergic reactions: Erythema nodosum (painful shin nodules), erythema multiforme.
    • "Desert Rheumatism": prominent arthralgias.
  • Disseminated Disease (<1%): Severe, occurs weeks to months later.
    • Risk: Immunocompromised (esp. T-cell), pregnant women (3rd trimester), certain ethnicities (Filipino, African).
    • Sites: Skin (nodules, ulcers), bones/joints (osteomyelitis), and CNS (meningitis).

⭐ Erythema nodosum + arthralgias + fever is a classic triad for primary Coccidioidomycosis, often tested as "Valley Fever."

Erythema Nodosum on Shins

Diagnosis & Treatment - Spherule Sleuthing & Attack

  • Microscopy/Histology: Key is identifying spherules (30-60 µm) containing endospores in tissue or sputum. Much larger than RBCs.
  • Culture: Definitive but highly infectious; lab must be notified.
  • Serology: IgM for recent infection; complement-fixing IgG titers correlate with disease severity.
  • Skin Test: Positive test only indicates exposure, not active disease.

Coccidioides immitis/posadasii spherule with endospores

⭐ Development of erythema nodosum ("desert bumps") is a hypersensitivity reaction indicating a good prognostic sign of a strong cell-mediated immune response.

High‑Yield Points - ⚡ Biggest Takeaways

  • Coccidioides is a dimorphic fungus endemic to the Southwestern US, causing Valley Fever.
  • It exists as mold in the soil and transforms into spherules containing endospores in the lungs.
  • Transmission is via inhalation of airborne arthroconidia, often after soil disruption (e.g., earthquakes).
  • While often asymptomatic, it can cause community-acquired pneumonia.
  • Disseminated disease (skin, bones, meninges) is a major risk in immunocompromised patients.
  • Look for erythema nodosum as a common hypersensitivity reaction.

Practice Questions: Coccidioides immitis/posadasii

Test your understanding with these related questions

A 44-year-old man comes to the physician because of a 3-week history of productive cough, fever, and lethargy. He also has several skin lesions over his body. His symptoms began 3 weeks after he returned from a camping trip in Kentucky. Three years ago, he underwent kidney transplantation for polycystic kidney disease. Current medications include sirolimus and prednisone. His temperature is 38°C (100.4°F). Diffuse crackles are heard over the lung fields. There are 4 white, verrucous skin patches over his chest and upper limbs. A photomicrograph of a skin biopsy specimen from one of the lesions is shown. Which of the following is the most likely diagnosis?

Image for question 1
1 of 5

Flashcards: Coccidioides immitis/posadasii

1/10

The route of transmission of _____ is through inhalation of spores in dust

TAP TO REVEAL ANSWER

The route of transmission of _____ is through inhalation of spores in dust

coccidioidomycosis (what fungus)

browseSpaceflip

Enjoying this lesson?

Get full access to all lessons, practice questions, and more.

Start For Free