[Manifestations of genotypic and phenotypic heterogeneity in populations of Shigella sonnei and of humans at different phases of the development of the epidemic process].

The study of the structure and developmental dynamics of S. sonnei populations and the state of local immunity to this infection in children under school age has revealed that the interaction of the heterogeneous populations of the parasite and the host is the internal motive force of the self-regulating phasic development of the epidemic process. In the course of this process complementary changes in the virulence of the infective agent and in the immunoresistance of children are generated on the basis of negative feed-back.