Serial Passage of Trypanosoma lewisi in the Heterologous Mouse Host. I. Development in Calorically-restricted Hosts.

SYNOPSIS. Two isolates ("A" and "B") of Trypanosoma lewisi from the same rat stock source were serially transferred in calorically-restricted mice supplemented daily with normal rat serum. The "A" strain was transferred consecutively through 300 mice over a period of more than 3 years and was voluntarily discontinued. The "B" strain died out spontaneously after 43 consecutive passages in mice. The developmental histories of these 2 isolates were analyzed and compared with respect to duration of the parasitemic period, interval to the next subsequent passage in mice, day of death of each host animal, proportion of host animals that died, intensity of parasitemia in mouse tail blood, interval required for development of the observed maximal parasitemia, and duration of maximal parasitemia.
"A" appeared to have become progressively adapted to the mouse as judged by a decrease in parasitemic period with successive transfer associated with a progressive increase in trypanosome population, and declines in the interval required for development of the observed maximal parasitemia and in the duration of this maximal response. There did not appear to be any correlation of the percentage of animals that died with any other factor. The "B" strain did not appear to have adapted itself to mice as judged by the foregoing criteria.