Pathophysiology
Clinical meaning
Coccidioidomycosis (Valley fever) is a systemic fungal infection caused by the dimorphic fungi Coccidioides immitis and Coccidioides posadasii, endemic to the arid and semi-arid regions of the Western Hemisphere, particularly the southwestern United States (Arizona, California's San Joaquin Valley, New Mexico, Texas, Utah, Nevada), northern Mexico, and parts of Central and South America. The disease derives its colloquial name 'Valley fever' from the San Joaquin Valley in California where the disease was first extensively characterized. Coccidioidomycosis is now the most commonly reported invasive fungal infection in the United States, with approximately 10,000-20,000 reported cases annually, though the true incidence is estimated at 150,000+ cases per year because the majority of infections are asymptomatic or mild and go unreported. Understanding the dimorphic lifecycle of Coccidioides is essential for comprehending its pathogenesis. In the environment, Coccidioides exists as a mold (saprophytic phase), growing as septate hyphae in soil. As the mycelial mat matures, alternate hyphal cells undergo autolysis, leaving behind barrel-shaped arthroconidia (arthrospores) approximately 2-5 micrometers in size. These arthroconidia are the infectious form and are remarkably resistant to environmental stress (heat,...