Studies on histoplasmosis I. Comparative virulence of variant and parent strain Histoplasma capsulatum in Hamsters

Summary 1. A variant strain ofHistoplasma capsulatum was isolated from a secondary colony in cultures of tissue from hamsters infected with the parent strain ofHistoplasma. The variant strain was found to differ from the parent strain in colonial morphology, stability of the yeast phase in subculture, and in growth rate.2. Results of virulence testing with these two strains showed the parent strain to be somewhat more virulent than the variant strain as measured by survival time and slope of the death rate curve over a 19 day period.3. Nevertheless, in view of the more rapid growth rate of the variant and its probable antigenic variation from the parent strain, the development of such a variant is viewed as an increased hazard to the host, particularly in a longer term infection.4. The repeated isolation of a variant strain ofHistoplasma suggests that strain variation may play a significant role in the outcome of naturally acquired infections.This work was initiated at the State University of New York, Downstate Medical Center, Brooklyn, N. Y., and supported in part by funds ((#12-1081) from the National Fund for Medical Education, grant # 12-1054.