Age Resistance of Mice to Trypanosoma cruzi

The trypanosome of Chagas' disease, Trypanosoma cruzi, is known to cause more severe infections in young persons than in adults, and when the organism is transferred to laboratory rats, mice, and rabbits, young animals likewise usually suffer more intense infections than older individuals (1-4). The guinea pig, on the contrary, is about equally susceptible to the parasite at all ages (3). Although mouse infections with Trypanosoma cruzi have been studied by several investigators, the precise age at which mice attain their comparative resistance is still uncertain since the specific ages of the animals used in the studies reported hitherto has not generally been known. In the present work, an attempt has been made to fix this age for mice, by studying carefully the relative susceptibility of mice of different known age groups. The infections were carried out both by intraperitoneal inoculation of the parasites and by their administration per os.