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Varying virulence in rabbits infected with different filamentous types of Histoplasma capsulatum
Abstract:
Histoplasma capsulatum filamentous primary isolates and their subcultures are separable into two distinct colonial types (A and B) having different microscopic characteristics. Yeast forms of the A and B types and the parent (P) strains from which they are derived are microscopically indistinguishable. Critically standardized inocula of living P, A, and B yeasts from one strain of H. capsulatum (G-184) were injected intravenously into 12 rabbits. Each type produced progressively debilitating disease, but in varying degrees. Of the 12 animals, 6 died within 2 to 14 weeks. A persisting copious nasal exudate, beginning at or before 1 week, was cultured weekly at 26 C on Mycosel (BBL) agar. Pure cultures of A and B filamentous type colonies were recovered from exudates of animals receiving A and B yeasts, respectively, whereas both filamentous types were isolated from rabbits injected with P yeasts, with B predominating. Only A and B yeasts thus maintained their filamentous integrity during animal passage. It was noted that dissemination of H. capsulatum through the nares of infected rabbits represents a possible hazard to laboratory personnel heretofore unrecognized. It is also a possible means of cross-infecting or sensitizing or cross-infecting and sensitizing animals housed in the same room, if A and B yeasts prove not to be antigenically identical.
Insights
Histoplasma capsulatum yeasts (A and B types) caused disease in rabbits, with nasal shedding observed. This highlights potential laboratory and animal transmission risks of Histoplasma capsulatum.
Area of Science:
- Mycology
- Infectious Diseases
- Veterinary Pathology
Background:
- Histoplasma capsulatum exhibits distinct colonial types (A and B) with differing microscopic features.
- Yeast forms of parent (P), A, and B strains are microscopically identical.
Purpose of the Study:
- To investigate the pathogenicity and dissemination of different Histoplasma capsulatum yeast types in a rabbit model.
- To assess the stability of filamentous integrity during animal passage.
Main Methods:
- Intravenous injection of standardized inocula of P, A, and B yeasts into 12 rabbits.
- Weekly culturing of nasal exudates on Mycosel agar.
- Microscopic and colonial characterization of isolated Histoplasma capsulatum.
Main Results:
- All yeast types induced progressive, debilitating disease in rabbits, with varying severity.
- Nasal exudates consistently yielded pure cultures of A and B filamentous types corresponding to the injected yeasts.
- Rabbits injected with P yeasts shed both A and B filamentous types, with B predominating.
- Filamentous integrity of A and B yeasts was maintained throughout animal passage.
Conclusions:
- Histoplasma capsulatum yeasts maintain their distinct filamentous types during infection and dissemination in rabbits.
- Nasal dissemination poses a potential hazard to laboratory personnel.
- Cross-contamination or sensitization risks exist among animals if yeast types are not antigenically identical.