Coccidioidomycosis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: ; Vidit Bhargava, M.B.B.S [2]; Aditya Ganti M.B.B.S. [3]

Overview

Coccidioidomycosis is a fungal infection, that is acquired through inhalation of the spores that is present in the environment. Following transmission, coccidioidomycosis are deposited into terminal bronchioles and enlarge, become rounded and develop internal septations to form what are known as the spherules. It then disseminates to the lymphatics and blood stream to gain access to any organ of the body.

Pathogenesis

The pathogenesis of coccidioidomycosis can be described in following steps.

Life cycle and epidemiology - Source: https://www.cdc.gov/

Transmission

• Coccidioiodomycosis exist as mycelia in the soil with septations.
• During hot climate or dry environment, they proliferate asexually, transforming into spores, known as arthroconidia.
• Infection is caused by inhalation of these arthroconidia.
• The disease is not transmitted from person to person.

Incubation period

• Incubation period of coccidioidomycosis varies from one to three weeks.

Dissemination

• Following inhalation, arthroconidia reach terminal bronchioles.
• Then they are ingested by pulmonary macrophages.
• Inside macrophages these arthroconidia enlarge, become rounded and develop internal septations to form what are known as the spherules.
• It then disseminates to the lymphatics and blood stream to gain access to any organ of the body.

Seeding

• Spherules contain uni-nuclear cells called as endospores which may propagate the infection further as they have the capability to develop into spherules.
• This conversion of arthroconidia into spherules initiates an inflammatory reaction and leads to a chemotaxic response (peptides derived from activation of the complement pathway, leukotrienes ) which attracts neutrophils and eosinophils to the site of inflammation.
• Cell mediated immunity keeps the infection in check and keeps them limited to the organ of origin by forming granulomas.

Immune response

Coccidioidomycosis elicits cell-mediated immune responses.

• Delayed type hypersensitivity to coccidioidal antigens is common after acute infection has resolved.
• Dissemination usually occurs via the lymphatics and is more common in immune suppressed in whom the primary infection is not contained.

Life cycle of coccidiodes

Genetics

There is no known genetic association to coccidioidomycosis.

Microscopic pathology

It is a dimorphic fungus and on microscopy, the following can be seen

• Spherule with endospores
• Rarely as hyphae in lung biopsy

Histopathological changes in coccidioidomycosis

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  Methenamine silver stain reveals reveals spherules of Coccidioides immitis in brain tissue. From Public Health Image Library (PHIL).

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  PAS-stained photomicrograph of an unknown tissue specimen revealed the presence of three Coccidioides immitis spherules. From Public Health Image Library (PHIL).

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  PAS-stained photomicrograph of an unknown tissue specimen revealed the presence of three Coccidioides immitis spherules. From Public Health Image Library (PHIL).

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  Photomicrograph of of pus from a Guinea pig, Cavia porcellus, reveals presence of numbers of Coccidioides sp. fungal sporangia. From Public Health Image Library (PHIL).

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  Photomicrograph of of pus from a Guinea pig, Cavia porcellus, reveals presence of numbers of Coccidioides sp. fungal sporangia. From Public Health Image Library (PHIL).

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  Histopathologic characteristics found within a pus specimen, prepared using potassium hudroxide (KOH). Specimen harvested from a skin lesion in a case of cutaneous coccidioidomycosis. From Public Health Image Library (PHIL).

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  Histopathologic characteristics found within a pus specimen, prepared using periodic acid-Schiff (PAS). Specimen harvested from a skin lesion in a case of cutaneous coccidioidomycosis. From Public Health Image Library (PHIL).

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  Histopathologic characteristics found within a pus specimen, prepared using periodic acid-Schiff (PAS). Specimen harvested from a skin lesion in a case of cutaneous coccidioidomycosis. From Public Health Image Library (PHIL).

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  Histopathology of coccidioidomycosis, lung. Methenamine silver stain. From Public Health Image Library (PHIL).

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  Histopathology of coccidioidomycosis, retroperitoneal area. From Public Health Image Library (PHIL).

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  Histopathologic changes due to coccidioidomycosis of the lung caused by Coccidioides immitis. From Public Health Image Library (PHIL).

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  Histopathologic changes in a case of coccidioidomycosis of the lung showing a large fibrocaseous nodule. From Public Health Image Library (PHIL).

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  Histopathology of coccidioidomycosis of lung. From Public Health Image Library (PHIL).

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