Molecular epidemiology of Cryptosporidium and Giardia infections.

For infectious diseases, molecular epidemiology can be defined as the use of molecular (predominantly genetic) methods to distinguish between strains of a microbial pathogen in order to identify markers of virulence or host range or to elucidate different transmission pathways. In this regard, molecular epidemiological methods have the same objectives as other typing methods that have been in use for several decades. The characteristics of a good typing method are typability, reproducibility and discriminatory power. There have been significant advances in typing methods for Cryptosporidium spp. in recent years. The first advances were for methods to distinguish the different species, predominantly C. parvum from C. hominis. More recently, microsatellite markers have been used to distinguish different strains within these two species. Microsatellite typing of C. parvum is sufficiently discriminatory to be useful, although more information is needed to determine reproducibility. Typing methods for C. hominis are not yet sufficiently discriminatory for general use. Molecular typing methods for Giardia are not yet well developed and have not been used in well-designed epidemiological studies.