A microsatellite marker reveals population heterogeneity within human and animal genotypes of Cryptosporidium parvum

Isolates of the protozoan parasite Cryptosporidium parvum have been differe ntiated into 2 genotypes: genotype 'H', which is associated only with human infections, and genotype 'C', which is associated with both human and anim al infections. To date, the analysis of polymorphisms of genes and of the s mall subunit ribosomal DNA have revealed no heterogeneity within the 2 geno types. In the present study, a locus containing simple sequence repeats (mi crosatellites) was PCR amplified and sequenced from 94 C. parvum isolates, which were collected from humans (immunocompetent and immunocompromized ind ividuals, outbreak and single cases) and from several animal hosts in 3 con tinents. The analysis revealed that genotype 'H' can be further differentia ted into 2 subgenotypes, and genotype 'C' can be further differentiated int o 4 subgenotypes. The 6 subgenotypes differ in terms of expansions/contract ions of the microsatellite repeats and by point mutations. Some subgenotype s showed a wide geographical distribution, whereas others were restricted t o specific regions. Therefore, microsatellites are informative markers for more defined studies on the epidemiology, the transmission routes, and the population structure of this parasite.