Cryptosporidium is a genus of parasites which has become a rising concern due to its presence in drinking water. The species that affects the most mammals, including humans, is Cryptosporidium parvum, which may cause gastrointestinal illness.
In individuals with healthy immune systems the disease may lead to watery diarrhea for up to several weeks, but in those with compromised immune systems the pathogen may be prolonged and even life-threatening.
Young children, people with compromised immune systems, international travelers, and people who drink from or swim in shallow or unprotected water are most at risk for this parasite. As in the case of similar parasites, Cryptosporidium gained prevalence during the AIDS epidemic, and gained importance as fatalies grew among AIDS patients with crytosporidiosis.