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Coccidioides Mold Species

Coccidioides immitis   is on the U.S. Government Occupational Safety and Health Administration [OSHA] list of biological agents and toxins that have the potential to pose a severe threat to public health and safety and that can potentially be utilized by terrorists.

Taxonomic Classifications

Kingdom: Fungi
Phylum: Ascomycota
Class: Euascomycetes
Order: Onygenales
Family: Onygenaceae
Genus: Coccidioides

Coccidioides immitis

laboratory culture at 25C

laboratory culture at 37C

laboratory culture at 41C

Tissue/Exudate Form

Above fungal identification is courtesy of

Picture of culture of Coccidioides immitis
Culture of
Coccidioides immitis

Picture of Arthroconidia of C. immitis
Arthroconidia of
C. immitis

On Sabouraud's dextrose agar at 25C, colonies are initially moist and glabrous, but rapidly become suede-like to downy, greyish white in color with a tan to brown reverse. However, considerable variation in both growth rate and culture morphology has been noted (Rippon, 1988). Microscopic morphology shows typical single-celled, hyaline, rectangular to barrel-shaped, alternate arthroconidia, 2.5-4.0 x 3.0-6.0 um in size, separated from each other by a disjunctor cell. This arthroconidial state has been classified in the genus Malbranchea and is similar to that produced by many non-pathogenic soil fungi such as Gymnoascus species.

WARNING: Cultures of Coccidioides immitis represent a severe biohazard to laboratory personnel and must be handled with extreme caution in an appropriate pathogen handling cabinet. C. immitis is a dimorphic fungus, existing in living tissue as spherules and endospores, and in soil or culture in a mycelial form. Culture identification by the exoantigen test is now the method of choice.

For further mold information about the Coccidioides mold species please visit this website:

Description and Habitats

Coccidioides immitis is a primary fungal pathogen which resides in soil of the desert Southwest.  Like most medically-important fungi that cause systemic disease, C. immitis demonstrates different morphologies in its saprobic and parasitic phases, but is distinguished from other fungal pathogens by the unique morphogenetic features of its growth in host tissue.


In reference to the information provided found in, Coccidioides immitis is the only species included in the genus Coccidioides.

Health Effects

Coccidioidomycosis is a nasty tongue-twister of a name, often contracted to 'coccy', for the disease caused by Coccidioides immitis. This fungus thrives in dry, saline soils, and is endemic in desert areas of the Southwestern U.S., where the disease is often called 'Valley Fever', because the organism is prevalent in the San Joaquin Valley of Central California and in Mexico (though it is strangely absent from the deserts of Africa and Asia). 

The process of infection, progress of the disease, and clinical symptoms, are very similar to those of histoplasmosis, though the fungus is not intracellular, and forms spherical structures containing spores. In culture, the same fungus produces chains of alternate thallic-arthric conidia, and has no known teleomorph. Millions of people in the U.S. Southwest have contracted the disease. Fortunately, as in histoplasmosis, most cases are benign, and healing is spontaneous. A few become systemic, and are usually fatal if untreated or misdiagnosed. The disseminated form of this disease is commoner among males than females, and among people with darkly pigmented skin.

In addition to, Coccidioidomycosis can also present as erythema nodosum or as a reactive arthritic condition which is commonly referred to as desert rheumatism.  It has been estimated, primarily on the basis of skin tests, that there are between 25,000 and 100,000 new cases of human C. immitis infections each year in United States.  Approximately 10 in 200 of these progress to disseminated disease.  A history of recurrent epidemics of coccidioidal infections, primarily in recreational and urban areas of the San Joaquin Valley, has focused attention on the need for both improved therapy and vaccine development.  

A recent Tucson news report claimed a 50% increase in the number of reported C. immitis infections during 1999 in Pima County, Arizona, and a 30% rise in the disease statewide.  The direct cost of medical supplies and sick leave for patients with Valley Fever has also escalated.  In Kern County, California, located near the epicenter of the endemic region in that state, the accrued cost of the disease from 1991 to 1995 was estimated at more than $66 million.  Vaccination of persons at risk of contacting coccidioidomycosis is a feasible approach to the control of this insidious fungal disease.  The rationale for immunoprotection is based on the observation that natural infection by C. immitis almost always confers lifelong immunity against the disease.

Geographic Distribution of Coccidioidomycosis


Coccidioidomycosis is primarily found in the desert regions of Southern California, Arizona, Nevada, New Mexico and West Texas.  This large area is home to about 20% of the population of the United States.  It also includes some of the most rapidly expanding cities in the nation and attracts large numbers of visitors each year.  The urban perimeters extend further into the desert each year, as exemplified by the Bakersfield region of California and the Phoenix-Tucson area of Arizona.  However, many cases of coccidioidomycosis have also been reported in regions which are not hyperendemic, such as San Diego and Los Angeles.  Outbreaks of coccidioidomycosis have occurred among archaeology students digging in prehistoric Indian sites in Northern California.  In 1977, a major dust storm blew soil from the San Joaquin Valley up into Northern California, including San Francisco, Marin County, Santa Clara, and Monterey County.  Immediately following the storm, numerous cases of coccidioidomycosis were reported in non-endemic regions of middle and Northern California.  At the time, there was some concern that C. immitis might be able to seed and persist in the soil in these areas, but that has not occurred.  The range of C. immitis includes West Texas and a large part of the desert regions of Northern Mexico.  A few cases of coccidioidomycosis have also been reported in Central and South America.  The largest South American endemic region is in Argentina where the climate is dry and the soil conditions are similar to those in the desert Southwest.  Despite these geographic limitations, physicians outside the endemic regions should consider coccidioidomycosis as a possible diagnosis of a respiratory infection if the patient has ever traveled through the desert Southwest or lived in an endemic area.  Reactivation of a prior asymptomatic C. immitis infection is potential concern for immunocompromised individuals.

The year 2001 has seen an interesting outbreak of this disease in Dinosaur National Monument, Utah.  Ten people who had been working at a 'dig' developed acute respiratory coccoidioidomycosis within two weeks of exposure.  All were treated with fluconazole, with an average hospital stay of 1.5 days, and released apparently none the worse for their experience.  New regulations for digs at Dinosaur call for watering down of the soil before digging, and use of approved respirators (N95). [from Bryce Kendrick's The Fifth Kingdom]

To learn more about this event, visit the web site:

Histopathology of coccidioidomycosis of lung. 
Mature spherule with endospores of Coccidioides immitis, intense infiltrate of neutrophils.
CDC/Dr. Lucille K. George (Above photo and caption is courtesy of:

Disseminated coccidioidomycosis, caused by Coccidioides immitis.

Macroscopic Features

Coccidioides immitis colonies grow rapidly. The colony morphology may be very variable. At 25 or 37C and on Sabouraud dextrose agar, the colonies are moist, glabrous, membranous, and grayish initially, later producing white and cottony aerial mycelium. With age, colonies become tan to brown in color.

Microscopic Features

Microscopic appearance of the fungus depends on the temperature of isolation:

1. At 25C

Hyphae and arthroconidia are produced. Hyphae are hyaline, septate and thin. Racquet hyphae may occasionally be observed on slides prepared from young cultures. Arthroconidia are thick-walled, barrel-shaped, and 2-4 x 3-6 m in size. Typically, these arthroconidia alternate with empty disjunctor cells. On the released arthroconidia, annular frills that are the remnants of the disjunctor cells are observed.

2. At 37C

Large, round, thick-walled spherules (10-80 m in diameter) filled with endospores (2-5 m in diameter) are observed. Production of spherules in vitro requires inoculation into a special synthetic medium, such as converse liquid medium, an incubation temperature of 37-40C and presence of CO2 at a concentration as high as 20%.

Coccidioides immitis continues to grow as a mold and does not produce spherules at any temperature unless special growth medium is provided in vitro. This finding indicates that temperature is not the only variable that controls the spherule formation. Thus, some authorities prefer not to classify this fungus as thermally dimorphic. Nevertheless, Coccidioides immitis is commonly classified among the thermally dimorphic fungi.

The definitive identification of an isolated Coccidioides immitis strain requires demonstration of spherule production in vitro, use of DNA probes, application of exoantigen tests, or demonstration of spherule production in vivo by animal experiments. Molecular typing studies have also been initiated and appear useful in identification.

Laboratory Precautions

The arthroconidia of Coccidioides immitis are very infectious. All manipulations should be done in a biological safety cabinet.


Amphotericin B, itraconazole, and voriconazole appear active in vitro against Coccidioides immitis. However, amphotericin B is less active against some of the isolates for which it fails to exert fungicidal activity. Itraconazole and voriconazole, on the other hand, do not have any fungicidal activity at all against Coccidioides immitis. Nikkomycins are additive to synergistic in vitro with fluconazole or itraconazole against Coccidioides immitis.

Patients with self-limited disease or relatively localized acute pulmonary infections usually do not require antifungal therapy. Antifungal therapy should be given to patients who have disseminated disease or are under risk of complications due to their underlying immunosuppression and other factors. Amphotericin B and azoles, such as fluconazole, itraconazole, and ketoconazole are used for treatment of coccidioidomycosis. However, clinical failure during antifungal therapy is not uncommon. Azoles, particularly fluconazole, is preferred for treatment of cases with meningitis. Available data suggest that the azole therapy should be continued life long in cases with meningitis to prevent relapses. Amphotericin B, if used for treatment of meningitis, should be given via intrathecal route and for a prolonged duration.

Animal experiments suggest that caspofungin, sordarins, and nikkomycins are also promising in treatment of coccidioidomycosis.

Concomitant surgical interventions may be required for some patients with pulmonary coccidioidomycosis as well as cases with bone and joint involvement.

The mycological information gathered and organized in this extensive research on the
different Pathogenic Molds was  sourced out from the list of websites below: | | | | | | | | | | | | | | | |


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