Trypanosoma lewisi: Physiologic adaptation of wild isolate to albino rats evidenced by cell populations and respiratory activity

Abstract

An isolate of Trypanosoma lewisi (designated as “D.C.”) was obtained from a feral rat in Washington, D.C., in December, 1965 and established in laboratory albino rats. At the 2nd, 15th, 28th, 41st, 54th, 67th, 80th, 93rd, and 121st consecutive passages in laboratory rats, the populations of trypanosomes in peripheral tail blood and the respiratory rates of recovered trypanosomes were determined at daily intervals throughout the natural sequence of events of the parasitemia. The control trypanosomal cell was the standard “L” form under continuous laboratory propagation in rats for many years. Technics of passage were identical for both isolates. Populations of the reference cell remained at relatively constant levels throughout the 2-year period of observations. Populations of the D.C. isolate increased at a calculated rate of about 0.65% per generation passage in rats. Endogenous respiratory rates and Q o 2 values with glucose and normal rat serum as substrates for the D.C. cell were all inferior to those of the reference cell. All Q o 2 values of the experimental cell increased as a direct function of the number of passages in rats. The orderly, progressive development of populations and oxygen uptake rates indicated that the D.C. isolate was undergoing physiologic adaptation to a new environment at a rapid rate. It was estimated from extrapolations that the experimental cell would approach the population and respiratory rate levels shown by the reference cell on about the 165th passage in laboratory hosts.