What is the mode of transmission for coccidiomycosis?

Mode of Transmission for Coccidioidomycosis

Coccidioidomycosis is acquired through inhalation of fungal spores (arthroconidia) of Coccidioides species (C. immitis or C. posadasii) that are present in the soil of endemic regions. 1, 2

Transmission Mechanism

• The primary mode of transmission is respiratory, occurring when a person inhales airborne arthroconidia
• The inoculum needed for infection can be as small as a single arthroconidium 1
• Spores become airborne when soil containing the fungus is disturbed

Events That Increase Risk of Exposure

• Natural events:

  • Dust storms
  • Earthquakes
  • Wildfires
  • Seasonal changes with dry conditions 3

• Human activities:

  • Construction work
  • Archaeological excavations
  • Highway construction
  • Agricultural activities
  • Military maneuvers
  • Recreational activities in endemic areas 3, 4

Geographic Distribution

• C. immitis:

  • California (especially central and southern regions)
  • Washington state (southeastern region)
  • Northwest Mexico 1, 2

• C. posadasii:

  • Southwestern United States (Arizona, New Mexico, Texas)
  • Mexico
  • Arid regions of Central and South America 1, 2

• Newly identified endemic areas:

  • Parts of Utah 5
  • Parts of Oregon 3
  • Northeastern Brazil (Piauí, Ceará, Maranhão, and Bahia) 6

Important Clinical Considerations

• Coccidioidomycosis is not transmitted person-to-person
• Without residence in or travel to endemic regions, persons almost never acquire coccidioidomycosis 1
• The disease typically manifests 1-3 weeks after exposure 1
• Approximately 60% of infections are asymptomatic 3, 6
• Risk of exposure is highest in areas with:
  • Low precipitation (12-50 cm of rainfall per year)
  • Few winter freezes
  • Alkaline soil 1

Prevention Strategies

• Avoid dust exposure in endemic areas
• Use respiratory protection (masks) during dust-generating activities
• Implement dust control measures during construction or excavation work in endemic regions
• Consider prophylactic antifungal therapy for high-risk individuals (e.g., organ transplant recipients) in endemic areas 2

Key Takeaway

Understanding that coccidioidomycosis is transmitted exclusively through inhalation of soil-borne spores is critical for diagnosis, as obtaining a history of residence or travel to an endemic area is essential for early identification of this infection 1.