Trypanosoma lewisi: Enhanced resistance in naive lactating rats and their suckling pups

Abstract

Lactating rats and their suckling offspring were shown to have a naturally occurring resistance to Trypansoma lewisi which was greater than that seen in normal adult rats and was not dependent on previous exposure to the parasite. In the case of the pups maximum protection was dependent on suckling being the sole source of nutriment and also on the peak of the parasitemia falling within the nursing period. Supplementary solid food reduced survival rates in concurrent Hemobartonella muris—T. lewisi infections: pups infected at 10 days of age and totally dependent on nursing showed 82.5% survival but only 6.6% survival when solid food was allowed to supplement milk. However, supplementary food did not reduce survival in pups infected with only T. lewisi. When pups were totally dependent upon nursing until the normal time of weaning (21 days of age), infection with H. muris—T. lewisi at the following days of age allowed the indicated mean survival rates: 10 days (82.5%), 20 (32.5%), 30 (14.3%), and 40 (100%). Infection with T. lewisi alone at the following days of age allowed the indicated mean survival rates: 10 days (100%), 15 (76%), 17 (52%), 20 (100%), and 30 (100%). Lactating rat serum agglutinated “adult forms” of T. lewisi, which correlated well with the observed sudden resolution of parasitemia in lactating animals at the time of the antigenic transition from “juvenile” to “adult” type. The “adult” stage parasitemia in suckling pups was selectively reduced when compared to that of nonlactating adult rats. The lactating rat serum factor could be passively transferred with lactating rat serum to animals already weaned.