Cryptosporidium is a genus of protists recognised as a major cause of diarrhoeal illness, contributing significantly to the global burden of gastroenteritis, especially in young children. Cryptosporidium is an apicomplexan traditionally considered a coccidian but is more closely related genetically to the gregarines. Cryptosporidium occurs worldwide but infection is especially prevalent where drinking water quality and sanitation are poor, and is most significant clinically in young children, malnourished people and immunocompromised patients.
The oocyst stage of the life cycle is shed in faeces of humans and animals and survives many environmental conditions and disinfectants. Oocysts have been detected in surface and ground waters, drinking water, wastewaters, treated and untreated recreational waters, soil and biofilm, and food and beverages including fruit and vegetables, juice, milk and shellfish. These can be transport vehicles from infected to susceptible hosts, in addition to direct transmission through person-to-person and animal contact.
Cryptosporidium oocysts can be detected by microscopy, immunological or molecular techniques. The 26 or so species can only be differentiated by molecular techniques as the oocysts are morphologically similar. Although many are host-adapted to animals, the most common species infecting humans are C. hominis, C. parvum and C. meleagridis, with geographic differences in species and subtype distribution. Despite description of several genotyping methods, there is no standardised method of investigating subtypes within species. The increasing availability of sequence data and whole genome sequences will help the discovery of suitable markers for multilocus genotyping. The limited ability to propagate Cryptosporidium spp. in culture and the lack of quantitative molecular methods for assessment of human infectivity potential (species; viability) of isolates in food, water and environmental samples hamper risk assessments.
Prevention and control measures include personal hygiene, effective sanitation and drinking water protection and treatment. There is a lack of effective specific therapy and no vaccine.