What is the role of spherules in the pathophysiology of coccidioidal infections?

Updated: Aug 27, 2019
  • Author: Duane R Hospenthal, MD, PhD, FACP, FIDSA, FASTMH; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

The presence of spherules triggers an acute inflammatory reaction. Spherules react with complement and promote chemotaxis of neutrophils and eosinophils. A mononuclear infiltrate may develop followed by subsequent conversion to polymorphonuclear predominance.

Pathogenicity of the organism is largely related to the resistance of the spherule to eradication by host defenses. Spherules and endospores produce no known toxins, and as new spherules are propagated in infected tissue, progressive suppuration and tissue necrosis occur. Neutrophils and mononuclear cells attempt phagocytosis of the organism, and giant cells are formed to attack larger fungal structures.

The body responds to the presence of the endospores with activation of complement and release of chemotactic factors. An intense, primarily neutrophilic, inflammatory reaction follows; however, the recruited neutrophils and macrophages are unable to kill the organisms because the spherules are resistant to phagocytosis. T-cell mediated immunity is important for killing and clearing of the organism; therefore, deficiencies in this arm of the immune system render the host of the fungus extremely vulnerable to disease and dissemination. [4]


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