Cryptosporidium is a protozoan parasite which causes the gastrointestinal disease cryptosporidiosis. This is characterised mainly by watery diarrhoea and abdominal pain and lasting for a couple of weeks. In immunocompromised individuals, the disease can be more severe andeven fatal.
Cryptosporidium oocysts are shed in the faeces of infected individuals and infection usually occurs through person-to-person spread, contact with animals or consumption of contaminated drinking or recreational water. After being ingested the oocysts excyst in the small intestine where they release sporozoites that attach to the microvilli of the epithelial cells. Whilst in the intestine, the parasites undergo a complex lifecycle before being excreted as robust oocysts. The parasite can continue to be shed even after symptoms resolve and the infected human or animal can excrete millions of oocysts in their faeces. Although the oocysts are unable to reproduce outside a host they are able to survive in the environment for many months and are resistant to several forms of disinfection Including chlorine.
Currently, there are 20 valid Cryptosporidium species and numerous “genotypes”, infecting in total over 150 host species. The major pathogens are Cryptosporidium hominis and Cryptosporidium parvum in humans and C. parvum in young animals. Other species are pathogenic to birds and reptiles. As few as single numbers of oocysts may cause infection and the environmentally robust nature of oocysts and resistance to chlorine disinfection ensure that cryptosporidiosis is a priority for water treatment professionals.