Viability and infectivity of two Cryptosporidium parvum bovine isolates from different geographical location.

The viability of two Cryptosporidium parvum bovine isolates from Spain and Colombia was evaluated by in vitro excystation, inclusion/exclusion of two fluorogenic vital dyes (DAPI and PI) and infectivity assay in a suckling murine model. Excystation percentages were similar for both Spain and Colombia isolates (83% and 87%, respectively). The total viability of the Spain isolate, measured by inclusion/exclusion of two fluorogenic vital dyes, was 71% in comparison with that detected for oocysts of the Colombia isolate, 32.3%. The bovine C. parvum oocysts of both isolates were viable and infectious for suckling Swiss CD-1 mice. However, infectivity percentage and the mean intensity of infection were consistently higher in the Spain isolate than those from Colombia isolate. It was not possible to obtain a good correlation between in vitro excystation, inclusion/exclusion of vital dyes and in vivo infectivity for the Colombia isolate, while data obtained with the Spain isolate indicated that there was an apparent strong correlation between excystation efficiency, total viability and the infectivity. Although a comparative analysis of genetic variation among these isolates from different geographical location is necessary, variations observed between the both isolates seemed to be a result of parasite adaptation to environmental stresses such as temperature which appears to have a direct effect on the permeability of the oocysts.