Radiosensitivity of Entamoeba histolytica cysts.

A dose of approximately 8,400 RAD noticeably lowered the number of viable cysts of E. histolytica in a clear, saline suspension, as calculated by the Most Probable Number method. Doses of approximately 16,700 RAD and more destroyed more than 99% of viable cysts. The relation between increasing cyst mortality and increasing gamma-ray dosage is represented by a logarithmic straight line. A difference of 21 hours in age had no demonstrable effect on response of cysts to irradiation. Cysts of the NBS strain are roughly one-tenth as resistant t,o gamma rays as are trophozoites of the same strain.