Molecular epidemiology of human cryptosporidiosis.

Species within the genus Cryptosporidium are protozoan parasites that infect a wide range of vertebrates, and represent a significant cause of morbidity and mortality in those animals. In humans, cryptosporidiosis is a common cause of diarrhoeal disease with a global distribution. Unravelling the epidemiology of human infection has proven to be difficult, due to the existence of multiple transmission routes (person-to-person, animal-to-person, waterborne, foodborne and airborne transmission), and to the difficulties in identifying the different species using conventional criteria, such as oocyst morphology. The advent of molecular techniques has had a remarkable impact on the way the epidemiology of cryptosporidiosis can be studied. Molecular investigations have shown that the vast majority of human cases are caused by C. hominis and C. parvum. Interestingly, differences in geographical and temporal distribution, disease presentations and risk factors for infection have been identified for both C. hominis and C. parvum. Further, molecular analyses have revealed that other species, including C. meleagridis, C. felis, C. canis, C. suis, C. muris and two Cryptosporidium genotypes, can infect humans and may be linked to clinical disease, not only in immunocompromised but also in immunocompetent individuals.