Excerpt from Coccidioidomycosis

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Background

In 1892, Alejandro Posada first defined coccidioidomycosis as a distinct disease. Coccidioidomycosis is caused by Coccidioides immitis, a dimorphic soil fungus native to the San Joaquin Valley of California, southern portions of Arizona, northern portions of Mexico, and scattered areas in Central America and South America.

C immitis propagates both as a saprophyte and as a parasite. In soil, it grows as a mold with branching septate hyphae. When the soil is disturbed, the hyphae fragment, which forms extremely hardy structures called arthroconidia, can become airborne. If inhaled by animals or humans, the arthroconidia can reach the pulmonary alveoli and transform into thick-walled multinucleate spherules, which form septa and produce hundreds to thousands of uninucleate endospores. Each endospore is capable of producing new spherules or mycelia.

Various other eMedicine articles on coccidioidomycosis are as follows:

• Coccidioidomycosis (Emergency Medicine)
• Coccidioidomycosis (Infectious Diseases)
• Coccidioidomycosis (Ophthalmology)
• Coccidioidomycosis (Pediatrics)
• Coccidioidomycosis (Pulmonology)
• Coccidioidomycosis, Thoracic (Radiology)

Pathophysiology

Almost all C immitis infections result from the inhalation of arthroconidia. Infection may be locally controlled, or it may spread within the lungs or via the bloodstream. In rare occurrences, an inoculation of C immitis causes primary cutaneous coccidioidomycosis with lymphatic extension to the regional lymph nodes; these cases resolve without treatment.

A single C immitis arthroconidium may be sufficient to produce a naturally acquired respiratory infection. The size of the arthroconidium allows it to be deposited in the terminal bronchiole but probably does not allow it to reach the alveolar space by means of direct inhalation. As an arthroconidium transforms into a spherule, the resulting inflammation results in a local pulmonary lesion. Extracts of C immitis organisms react with complement, leading to the release of mediators of chemotaxis for neutrophils.

In some patients, C immitis leaves the lungs to establish disseminated lesions in distant parts of the body. To establish extrapulmonary sites of infection, the fungal elements must move from the bronchiole into the lung parenchyma and enter and leave the vascular space. In some instances, endospores in the macrophages travel through the lymphatics, reaching the bloodstream. This process is reflected in the common finding of infected hilar, peritracheal, and cervical lymph nodes in patients with extrapulmonary coccidioidal infections. T lymphocytes are of paramount importance in controlling C immitis infections.

Frequency

United States

Approximately 25,000 new, clinically evident cases of coccidioidomycosis are reported annually in the United States, with as many as 75 deaths per year resulting from the infection.

C immitis is endemic in the soil in certain regions of the Western Hemisphere, almost all of which are located between latitudes 40° north and 40° south. In the United States, C immitis is endemic in California's Central Valley and in southern parts of Arizona. It also is endemic in certain places in Utah, Nevada, New Mexico, and Texas. New infections frequently occur during the summer months after the soil dries. In Arizona, a second peak of new clinical infections occurs in October, which corresponds to a similar dry period after the summer rains in that region.

Coccidioidomycosis in Arizona increased in incidence from 1990-1995.¹ The number of reported cases increased from 255 (7 cases per 100,000 population) in 1990 to 623 (14.9 cases per 100,000 population) in 1995.

International

In addition to regions in the United States, other areas in which C immitis has been identified include northern parts of Mexico adjacent to the Sonoran region of Baja California, Central America (Nicaragua, Honduras, and Guatemala), and South America (Argentina, Columbia, Venezuela, and Paraguay).

Mortality/Morbidity

• Mortality rates of fulminant infection remain high despite appropriate treatment. In recently published data, of patients in Arizona the hospitalized for it, 48 died, and 12 (25%) of these patients had a concurrent diagnosis of human immunodeficiency virus infection.¹
• The infection causes as many as 75 deaths per year in the United States.
• This endemic fungal infection of the southwestern United States causes morbidity and mortality among solid organ transplant recipients who reside in or visit the endemic area or who receive organs from donors infected with the fungus.²

Race

• Filipinos have the highest risk of dissemination or progressive pneumonitis.
• African Americans, followed by Mexicans, also appear to have an increased risk for disseminated infection, though their risk is lower than that of Filipinos.

Sex

Pregnant women are more likely to acquire disseminated coccidioidal infection, especially in the third trimester or in the immediate postpartum period.

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