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Coccidioidomycosis

Coccidioidomycosis is an infection which causes a varying response from the authors of textbooks on tropical diseases, as it does in patients. The causative fungus, Coccidioides immitis, occurs naturally only in some part of the Western Hemisphere. Some tropical texts ignore the disease completely, but in others it is described at length. As with many other diseases in this book, it can occur in both tropical and subtropical regions, particularly in those which are relatively arid.

Synonyms

Valley fever. Desert rheumatism. The bumps. California disease. Posada's disease. Wernicke's disease. Coccidioidal granuloma. San Joaquin fever. Fr: Coccidioidomycose. Ger: Kokzidioidomykosa. Talfieber. Wustenfieber. Sp: Coccioidomicosis.

Definition

Coccidioidomycosis is a mycotic infection caused by Coccidioides immitis (the species name, "immitis" means "not mild").

Geographic Distribution

The infection is hyperendemic in the southwestern United States (in some regions of the San Joaquin Valley up to 97% of children may have positive skin reactions). It is also endemic in Mexico, Guatemala, Honduras, Colombia, Venezuela, Bolivia, Paraguay, Argentina, and Brazil, particularly where there are semiarid or desert regions. Sporadic infections have been identified in Europe, Japan, Asia, Canada, and Australia amongst individuals who have been exposed in the endemic areas or to products from those areas.

Epidemiology and Pathology

The first patient was described in 1891, a soldier with a skin infection in Northern Argentina. He survived for over 11 years, during which time he was studied by Posadas and Wernicke: hence the synonyms. The infection has been studied extensively since then, and there are at least five textbooks titled "Coccidioidomycosis." There are innumerable reports and reviews in general and specialized medical journals: here is yet another!

Coccidioides immitis is found as a saprophytic mold in soils in endemic areas. The molds produce infective arthroconidia or arthrospora. Infections are usually the result of inhalation of fungus from dust. Rarely, traumatic introduction of the fungus into the skin has resulted in disease. Many mammals have been infected, some wild, but also those housed in zoos in the endemic areas. Wild rodents and rattle and gopher snakes have been infected in nature.

In endemic areas, dust is laden with highly infective chlamydospores which are round, nonbudding, thickwalled spherules containing numerous endospores: these develop into branching, septate filamentous hyphae which form anthrospores, found in both nature and culture. The chains of thick-walled barrel-shaped arthrospores (arthroconidia) which grow on cultures alternate with empty cells, which is an important though nonspecific diagnostic characteristic.

Coccidioides immitis is a dimorphic fungus. When inhaled, the arthrospores enlarge and become rounded to produce spherules. The spherules produce as many as 800 endospores; these, when released into tissues, can mature into new spherules and the lifecycle starts again. When infected tissue or body fluid is cultured, the hyphae form develops from the spherule-endospore form. The tissue reaction is both suppurative and granulomatous, with caseation and granulomas formed of giant cells and macrophages. As healing occurs, there is fibrosis and calcification. The extent of the necrosis and the pace of healing depend on the size of the infected dose and the immune status of the patient. Thus, it is in the immunosuppressed that severe pulmonary or disseminated infections are likely to occur. Nevertheless, clinically silent infections, recognized only by positive skin reactions, are very common in endemic areas.

Patients with competent cell-mediated immunity convert their coccidioidin skin test within 2-21 days after clinical symptoms begin. Conversion is a useful way to make a diagnosis, but it must be confirmed histopathologically, by culture, or serologically. Positive skin tests may revert to negative (anergy) if the patient's immunity fails, which usually indicates that the infection is disseminated. Unfortunately, the cutaneous test is not completely reliable because cross-reactions with other fungal infections can occur or the test may be negative despite frank disease.

There are serological preciptin, complement fixation and immunodiffusion tests which can help with the diagnosis and assessment of progress and treatment. When infections are asymptomatic, less than 10% of the patients will have positive complement fixation titers. When there is meningitis, antibodies will be found in the spinal fluid, with reduced sugar, elevated proteins, and cells. When there is pulmonary infection, sputum culture is frequently positive. Urine samples may yield the organism in some patients with disseminated disease.

 

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Copyright: Palmer and Reeder