Patterns of development of Trypanosoma cruzi in the embryonated chicken egg

Blood forms of four strains of Trypanosoma cruzi were inoculated on the chorioallantois or intra-yolk sac in seven to nine day embryonated chicken eggs which were reincubated thereafter at 37-5-39-0 degrees C or at 32-34 degrees C. There were no significant differences between strains when total rates of infected eggs were compared. However, the highest proportions of positives, for every strain, were found among eggs inoculated into the yolk sac and reincubated in the lower temperature range. The most striking observations were: (a) independently of the route of inoculation, all strains developed through all stages of the invertebrate cycle within the embryonic cavities of eggs reincubated at 32-34 degrees C; (b) in a high proportion of these same eggs, all stages of the vertebrate cycle could be also found in the tissues of the embryo itself and its membranes; (c) no stages other than those characteristic of the vertebrate cycle could be found in the tissues of the embryo and its membranes among eggs maintained above 37 degrees C. It is thought that temperature is important in the transformation phases of the protozoon and that above 37 degrees C there was no conversion from the blood trypomastigotes to culture forms. Other transformation phases are probably also temperature-dependent, and strain differences in sensitivity to this factor are suggested. It is suggested that the embryonated chicken egg offers a suitable means for the study of the determinism of transformation in the cycles of T. cruzi and, possibly, also for helping in strain characterization.