Giardia and Cryptosporidium

Giardia and Cryptosporidium are gastroenteric parasites. They colonise the intestines of many animals and humans and their cysts or oocysts are shed in the faeces. They cause chronic to severe gastrointestinal upsets in humans, which may be characterised by chronic diarrhoea, foul wind and stomach cramps. Giardiasis is treatable and has never been known to be fatal. However, there is no known treatment for Cryptosporidium. Cryptosporidiosis is usually self-limiting, but in the case of immunocompromised patients eg AIDS sufferers, it may be fatal.


Giardia is spread in water by cysts and Cryptosporidium via oocysts. These are resistant infective stages. Giardia cysts are about 12 µm in length, football shaped and susceptible to some disinfection systems. Cryptosporidium oocysts are about 4 µm , spherical and resist most treatment systems. Routine testing for Giardia and Cryptosporidium, to comply with current water standards and water quality legislation, is now available