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Pathogenesis and electron microscopic changes of spherulogenesis of Coccidioides immitis (valley fever)
Abstract:
Pathogenesis and electron microscopic changes of spherulogenesis of Coccidioides immitis were determined. The organism showed a strong affinity for lung tissue, with granuloma developing in 100% (n = 40) of animals after subcutaneous and intraperitoneal inoculation. Intranasal instillation of the arthrospores resulted in moderate granuloma, with a markedly low frequency rate of infection in 11 animals (55%). Intradermal inoculation and skin scarification did not induce systemic infection. Unlike other routes used to induce infection, only 30% of the mice showed cutaneous changes, whereas in the group infected by skin scarification, 25% of the animals revealed pathologic changes. Indurated tiny nodular lesions developed in the skin at the site of the inoculation. The lesions did not ulcerate, and complete resolution was observed in 4 to 6 weeks. Electron microscopy of the spherulogenesis showed that the tissue form of the fungus replicated in the host tissues by segmentation of the innermost stratum of the wall of the spherule. The layer appeared to function as a germinating center, and as many as 8 spores of irregular size and shape were produced within a kidney-shaped segment. Many segments were in each spherule. The spores were separated, pushed more centrally, and became rounded to become the endospores. When the endospores were freed, each developed into a spherule.
Insights
Coccidioides immitis preferentially infects lung tissue, causing granulomas. Electron microscopy revealed fungal replication via spherulogenesis, where segmented walls produce endospores within host tissues.
Area of Science:
- Mycology
- Pathogenesis
- Immunology
Background:
- Coccidioides immitis is a fungal pathogen responsible for coccidioidomycosis.
- Understanding its pathogenesis and replication is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the pathogenesis of Coccidioides immitis infection through various inoculation routes.
- To elucidate the electron microscopic changes during spherulogenesis, the fungus's replication process in host tissues.
Main Methods:
- Subcutaneous, intraperitoneal, intranasal, intradermal inoculation, and skin scarification in animal models.
- Electron microscopy to examine fungal morphology and replication within host tissues.
Main Results:
- Subcutaneous and intraperitoneal inoculation led to 100% granuloma formation in lungs.
- Intranasal instillation resulted in moderate granulomas but low infection rates.
- Cutaneous inoculation caused localized lesions with complete resolution in 4-6 weeks; electron microscopy detailed spherule wall segmentation and endospore formation.
Conclusions:
- Coccidioides immitis demonstrates a strong affinity for lung tissue, with varying infection rates depending on the inoculation route.
- The study elucidated the mechanism of fungal replication through spherulogenesis at the ultrastructural level.