Selection of Cryptosporidium Parvum subpopulations by serial passages in mice.

The response of a natural Cryptosporidium parvum isolate to selective pressure was studied. It was hypothesized that separate populations could be obtained from a natural isolate. Parasites were selected on the basis of the temporal development in the mouse, specifically by isolating those completing their life cycle early and late in the infection cycle. According to this model, repeated sampling of Cryptosporidium during the initial or terminal phase of the infection would lead to the isolation of subpopulations with altered genotypes as well as phenotypes. Oocysts from isolate JRL-HIV were used to infect mice and oocysts excreted in the feces in the early and late phase of the infection were separately and serially propagated thereafter. We observed that over the course of the passages, those oocysts from early line were more virulent than the parasite line originating from oocysts produced late during the infection. In contrast, the temporal pattern of development was only affected after multiple rounds of selection