Population genetics of Cryptosporidium parvum.

Research on the population genetics of Cryptosporidium parvum is showing exciting developments. A study of numerous C. parvum isolates of human and animal origin collected in a small area of Scotland has uncovered differences in the epidemiology of what was originally referred to as C. parvum type 1 (also, anthroponotic type) and type 2 (zoonotic type), a designation recently changed to C. hominis and C. parvum. This study, based on fingerprints obtained from eight polymorphic genetic markers, showed striking differences between the population structure of these species; a clonal C. hominis population and a more complex C. parvum population. The population structure of C. hominis was consistent with the epidemic nature of human infections, where a small number of genotypes predominate. In contrast, C. parvum (type 2) genetic fingerprints showed evidence of random mating among genetically diverse parasites. Evidence for partitioning of the species according to host (human and bovine) was also inferred from these data. Two questions we are left with are whether these observations are specific to this particular location, where human transmission is relatively infrequent, and whether regions with high prevalence of human cryptosporidiosis will show more complex structures in both species. If substructuring into human-and bovine-derived C. parvum (type 2) is consistently observed, the potential for zoonotic transmission of C. parvum may also have to be reexamined.

Widmer G. Population genetics of Cryptosporidium parvum. Trends Parasitol 2004;20:3-6;discussion 6. Available at: http://dx.doi.org/ 10.1016/j.pt.2003.10.010