Figure 1.

Life cycle and transmission of Cryptosporidium. Thick-walled sporulated oocysts are released in the feces of infected hosts (1) that contaminate food and water sources (2). Transmission occurs mainly by ingestion of contaminated water or food by susceptible hosts (3). Following ingestion, oocyst ruptures (4a) to release four sporozoites (4b). Sporozoites exhibit gliding motility, enter the host epithelial cells and mature into trophozoites (4c), which undergo three rounds of asexual multiplication to produce meronts (4d) that invariably release eight merozoites (4e). Merozoites released from the third round of asexual proliferation give rise to the sexual stages upon reinvasion of host cells: the male microgamonts (4f) and the female macrogamonts (4g). Microgametes released from the microgamont penetrate and fertilize macrogamonts to form diploid zygotes (4h). The zygotes undergo meiosis and sporogony generating either thin-walled (4i) or thick-walled (4j) oocysts, each containing four haploid sporozoites. Thick-walled oocysts are released into the lumen of the intestine and excreted into the environment, where they are instantly infectious. The thin-walled oocysts, in contrast, excyst to cause autoinfection in the same host. Adapted with modification from (CDC, 2019). Created with BioRender.com.