Abstract
In a study of the transmission of the rickettsiae of the American spotted fevers by O. parkeri, 12 expts. were performed with spotted fever of the U. S., 10 with the spotted fever of Colombia and 4 with the spotted fever of Brazil. Guinea pigs were used for all infective and test feedings. O. parkeri stock from 6 Western States were employed with 7 human, 1 Dermacentor andersoni, and 1 rabbit tick (Haemaphysalis leporis-palustris) strain of spotted fever of the U. S., and one spotted fever strain from each of Colombia and Brazil. Transmission was effected by [male][male] and [female][female], through the egg, and by the larvae and all nymphal stages. Females that failed in transmission gave rise to infective progeny. Transmission through the ovum was observed in spotted fever of the U. S. to the F4 generation, in the spotted fever of Colombia to the F2, and in the spotted fever of Brazil to the F1. Ticks that had fasted for 1 year produced typical infections and progeny of these fasting ticks produced infections resulting in the death of the host. The data submitted affords further biologic evidence of the identity of these 3 immunologically identical infective agents and suggests that O. parkeri may be a factor in the maintenance of spotted fever in nature in the U. S. and occasionally, at least, a vector to man.