The life cycle of Cryptosporidium is complicatedconsisting of both sexual and asexual developmental stages. Infection beginswith the ingestion by the host of the sporulated oocysts through contaminatedwater or food or directly via the faecal-oral route. Inhalation of the oocystscan also occur. Each oocyst contains four sporozoites which after excystationin the intestinal lumen or the respiratory tract, emerge and invade theepithelial cells and develop into trophozoites. Trophozoites undergo asexualdivision (merogony) and form Type I Meronts consisting of 8 merozoites. Some ofthese merozoites form Type II meronts which contain 4 merozoites and initiatethe sexual phase of the life cycle. Macrogametocytes and microgametocytes areformed, fertilize and produce the zygote.
Most of the zygotes develop intooocysts, the thick ones with a two-layered wall which are released to theenvironment, and the thin-walled oocysts which facilitate autoinfection (Thompson et al., 2005).