Introduction: - Coccidioides posadasii

Coccidioides posadasii is a pathogenic soil fungus and is the causative agent of coccidioidomycosis, also known as "valley fever," in humans. It is endemic in southwest United States, Northern Mexico, and certain areas in Central and South America. Inhalation of the dry arthroconidia of Coccidioides sp. initiates the infection. Activities and professions related to tillage of the soil, such as agricultural work, telephone post digging, archeology, or simply playing with soil appear to be associated with development of coccidioidomycosis.

Coccidioidomycosis affects otherwise healthy immunocompetent hosts due to the true pathogenic nature of the fungus. It may be fatal in immunocompromised patients or in older people. Coccidioidomycosis has also been described in warm-blooded water animals such as bottlenose dolphins and horses.

C. posadasii is commonly classified as a thermally dimorphic fungus. It produces arthroconidia and hyphae. Arthroconidia produce large thick-walled spherules filled with endospores which, in turn, mature into spherules in the infected host tissue. No sex is known in this species.

The genus Coccidioides includes only two species, C. immitis and C. posadasii. Until 2002, C. posadasii did not exist as a separate species. It was recognized as a non-California variant of C. immitis.The two species can be distinguished only by genetic analysis and different rates of growth in the presence of high salt concentrations (C.posadasii grows more slowly). The differences in pathogenicity between two species are yet to be discovered.