Studies on Histoplasma Capsulatum Part 1. Fungus Virulence and Histopathology in CF-1 Mice Inoculated with Histoplasma Capsulatum Okayama-56 (Yamato)

Mycological and histopathological characteristics of the yeast phase of an isolated fungus, Histoplasma capsulatum Okayama-56 (Yamato), cultured at 37°C were investigated and the results obtained were as follows: 1. The lethality within 4 weeks in the mice of seven inbred lines given 1.0 mg of the culture intravenously was to be compared as, CF-1=dba-2>> AKR>BALB/c>A>ddT=C57 Br/cd. 2. The minimum lethal dose of CF-1 mice was 1.2 mg by means of intravenous injection. 3. The lethality within 4 weeks of CF-1 mice administered 1.0 mg of the culture intracranially, intravenously, intraperitoneally and by inhalation was 90, 80, 40 and 30 per cent respectively. 4. The most extensive and general pathologic changes were observed in the mice received intravenous injections, and in other cases the lesions produced were more or less localized at the site of invasion. The nature of changes was mostly to be interpreted as productive and granulomatous inflammations of the reticulo-endothelial system. 5. Small form fungi were well distributed in the reticulo-endothelial system and a small number of large form ones were seen in desqumative epithelial cells and in necrotic lesions. 6. The large form organisms were polymorphous being 5 to 20 μ in diameter and budding and chain-formation were infrequently observed. They were not appreciably stained with hematoxylin and eosin, but readily demonstrated by Gridley's stain. 7. The presenting pathologic appearances reached their peak in 2 to 3 weeks and then signs of improvement started to develop.