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In a survey of the wild rodents of Alberta it was found that 14 animals contained within their lungs fungous cells so large as to be visible to the naked eye. From the lungs of eight of these infected animals, Haplosporangium parvum was obtained in culture. The position of the fungus among the Phycomycetes is confirmed by a study of the reproductive structures, which may be interpreted as sporangia containing one or, rarely, several spores. H. parvum grows and sporulates upon soil. The sporangia are adhesive and transferred by contact. At 37 °C. they enlarge as much as 10 times their original diameter to form thick-walled chlamydospores that will germinate at room temperature. The parasite within the lung has a diameter as much as 50 times that of the sporangium from which it must have originated. Infected lungs usually show little reaction. Only one lung was frankly granulomatous. Some human systemic Phycomycetes, like H. parvum, are filamentous in their saprophytic phase and unicellular in their parasitic phase. Three of them, Blastomyces dermatiditis, B. brasiliensis, and Histoplasma capsulatum, are closely related to H. parvum. In their saprophytic phase they all reproduce by adhesive conidia that may be interpreted as sporangia with single endospores, while in their parasitic phase no sporangia have been observed. Coccidioides immitis is less closely related to H. parvum. When growing saprophytically it reproduces by air-borne oidia; when growing parasitically, by endospores. |
