Isolates of the protozoan parasite Cryptosporidium parvum have been differentiated into 2 genotypes: genotype ‘H’, which
is associated only with human infections, and genotype ‘C’, which is associated with both human and animal infections.
To date, the analysis of polymorphisms of genes and of the small subunit ribosomal DNA have revealed no heterogeneity
within the 2 genotypes. In the present study, a locus containing simple sequence repeats (microsatellites) was PCR
amplified and sequenced from 94 C. parvum isolates, which were collected from humans (immunocompetent and
immunocompromized individuals, outbreak and single cases) and from several animal hosts in 3 continents. The analysis
revealed that genotype ‘H’ can be further differentiated into 2 subgenotypes, and genotype ‘C’ can be further differentiated
into 4 subgenotypes. The 6 subgenotypes differ in terms of expansions/contractions of the microsatellite repeats and by
point mutations. Some subgenotypes showed a wide geographical distribution, whereas others were restricted to specific
regions. Therefore, microsatellites are informative markers for more defined studies on the epidemiology, the transmission
routes, and the population structure of this parasite.