Coccidioidomycosis—A Fungal Disease of the Americas

Coccidioidomycosis is a fungal disease found only in the Western Hemisphere. It is caused by two nearly identical species, Coccidioides immitis and C. posadasii, generically referred to as the “Californian” and “non-Californian” species respectively [1]. The fungus grows in a mycelial phase (see Box 1) in the soil within a geographically delineated area of the United States known as the Lower Sonoran Life Zone [2]. This semiarid zone encompasses the southern parts of Texas, Arizona, New Mexico, and much of central and southern California (Figure 1). Endemic regions for coccidioidomycosis have long been identifi ed in semiarid areas in Mexico [3], and smaller endemic foci have been described in areas of Central and South America [4,5]. More recently, Brazil has also been found to contain endemic areas in the semiarid northeastern states of the country [6]. The climatic conditions and fl ora of these states are similar to those in endemic regions in North, Central, and South America. In Latin America, Mexico has the largest number of reported cases, with the prevalence of infection in northern Mexico reported to be between 10%–40% [7,8]. C. posadasii is thought to be the predominant species in Mexico [3]. As the soil dries or nutrients become limiting, the fungus reproduces asexually by disarticulating the hyphae into small, environmentally-resistant arthroconidia (reproductive spores) (Figure 2). These are easily aerosolized when the soil is disturbed by wind or human activities. Consequently, it is the inhalation of the dust-borne arthroconidia that leads to infection by this pathogenic fungus in both humans and domestic or wild mammals. Upon inhalation, the fungus converts to a unique life cycle of alternating spherules and progeny endospores, which comprises the parasitic phase of this dimorphic fungus (Figure 2) [9]. Mycelial elements are only occasionally found in diseased tissue [10]. Coccidioidomycosis is not contagious; reports of human-tohuman spread are extremely rare. Hence, primary exposure to contaminated dust is the sole risk factor for the acquisition of this disease. It is estimated that upwards of 100,000 primary coccidioidal infections occur in humans each year in the endemic areas of the United States [11]. In recent years, the incidence of the disease has increased in California and Arizona , which may be partially due to the rapid immigration of previously unexposed persons from states outside the endemic areas (in other words, the pool of susceptible people has increased) [12]. In the United States, diagnosis in patients who have Coccidioidomycosis— A Fungal Disease of the Americas