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Primary acute histoplasmosis in guinea pigs exposed to aerosolized Histoplasma capsulatum
Abstract:
Guinea pigs were examined as a possible in vivo model for human histoplasmosis. Guinea pigs were exposed to an aerosol of viable microconidia and mycelial fragments of Histoplasma capsulatum generated in a Henderson apparatus. Colonization and infection of the lungs occurred, with subsequent involvement of the regional lymph nodes and reticuloendothelial organs. Cultural recovery of the fungus from the nasopharynx and bronchoalveoli was initially high, but decreased with time. The mean number of colonies recovered from the lungs gradually increased, reaching a peak at 2 weeks, with involvement of the regional lymph nodes. Extrathoracic dissemination to the liver and spleen occurred in only a few animals. After 4 weeks, all tissues except the cervical and tracheobronchial lymph nodes were culturally negative; all specimens were culturally negative after 8 weeks. Disappearance of H. capsulatum from tissues appeared to correlate inversely with the development of hypersensitivity as measured by skin test reactivity. Histopathological studies supported cultural results and were similar to those described for primary human and canine histoplasmosis.
Insights
Guinea pigs effectively model human histoplasmosis, showing lung infection and lymph node involvement. The fungus cleared from most tissues within 8 weeks, correlating with developing hypersensitivity.
Area of Science:
- Mycology
- Infectious Diseases
- Animal Models
Background:
- Histoplasmosis is a significant fungal infection.
- An ideal animal model is needed for studying human histoplasmosis.
- Guinea pigs have not been extensively studied as a model for this disease.
Purpose of the Study:
- To evaluate guinea pigs as a viable in vivo model for histoplasmosis.
- To characterize the infection dynamics and host response in guinea pigs exposed to Histoplasma capsulatum.
Main Methods:
- Guinea pigs were exposed to an aerosol of Histoplasma capsulatum microconidia and mycelial fragments.
- Fungal presence was assessed through culturing tissues (lungs, lymph nodes, spleen, liver, etc.) over 8 weeks.
- Histopathological examinations and skin test reactivity were used to measure host response and hypersensitivity.
Main Results:
- Infection established in the lungs, spreading to regional lymph nodes and reticuloendothelial organs.
- Fungal recovery peaked in lungs at 2 weeks, with transient nasopharyngeal and bronchoalveolar presence.
- Extrathoracic dissemination was limited; most tissues cleared the fungus by 4 weeks, and all by 8 weeks.
- Fungal clearance inversely correlated with skin test-detected hypersensitivity.
Conclusions:
- Guinea pigs serve as a suitable in vivo model for histoplasmosis, mimicking key aspects of human and canine infections.
- The model allows for studying the course of infection, fungal clearance, and the development of host immune responses, including hypersensitivity.