Molecular epidemiology of human cryptosporidiosis in developing countries.

Genotyping and subtyping tools have been used to characterize the transmission of human cryptosporidiosis in developing countries. Thus far, five Cryptosporidium spp. - C. hominis, C. parvum, C. meleagridis, C. canis and C. felis - are responsible for most Cryptosporidium infections in both immunocompetent and immunocompromised individuals. In most areas, C. hominis is responsible for over 70% of human cryptosporidiosis cases, with C. parvum accounting for 10-20% of infections. Differences have been observed among endemic areas in the proportion of infections due to each species, and in some areas C. meleagridis is also endemic. Results of subtyping suggest that there is high genetic heterogeneity in C. hominis in developing countries, and in these areas, human infections with C. parvum and other species are mostly the result of anthroponotic rather than zoonotic transmission. There is geographical segregation in C. hominis or C. parvum subtypes. Mixed and sequential infections with different Cryptosporidium species/genotypes and subtypes are common. Differences in oocyst shedding and clinical presentation have been observed among Cryptosporidium species and C. hominis subtypes. These findings reveal the diversity of cryptosporidiosis transmission in endemic areas and highlight the need for more extensive studies of cryptosporidiosis epidemiology in diverse areas with a wide spectrum of socioeconomic and environmental conditions.