Trypanosoma lewisi: duration of immune state in rats.

Abstract

Rats infected with Trypanosoma lewisi were studied for more than 500 days to measure the duration of the immune state. Sixty rats arranged in groups of ten were each inoculated with 100 cells of T. lewisi on Day 1. Subsequently, the first group was re-inoculated with the same number of trypanosomes on Day 56. On Day 141 the first group was again challenged and the second group was challenged for the first time. On Day 234 the first group was reexposed for the third time; the second group for the second, and the third group of rats was reexposed for the first time. This pattern was continued at Days 324, 414 and 505 when the 1st group was reexposed for the first time. Additional rats were inoculated on each challenge date for control of viability of the trypanosomes. Techniques for detection of parasites in the host's body were: (a) wet films of tail blood; (b) permanent blood smears; and (c) subinoculation of host blood into susceptible animals (xenodiagnosis). The immune state was steady in all groups during the periods of observation. No active trypanosomes were detected at any period of observation. However, inactive or dead trypanosomes were found in the peripheral blood of rats reinoculated on Day 414 and 505. Control animals showed active parasitemias during each reinoculation period.