Cryptosporidiosis is one of the most common waterborne diseases. The main symptom in immunocompetent individuals is a self-limiting short term watery diarrhoea with symptoms lasting for on average one week and is treated mainly symptomatically. The very young, old and the immunocompromised patients may develop more severe cryptosporidiosis.

The causative agent of the diarrheal illness, C. parvum, is a protozoan parasite that infects the intestine of humans and animals (mainly cattle, sheep and goats). Infection occurs by the faecal oral route via water, soil or food that has been contaminated with faeces of an infected individual or animal. After ingestion, C. parvum undergoes a complicated life cycle including asexual and sexual stages finally leading to 2 different types of oocysts. The thin walled oocysts reinfect the host; the mature thick walled oocysts are excreted in the stool. Infected humans shed most oocysts during the first week of infection but shedding will continue for weeks after the end of the diarrhea. Oocysts are highly infective; 2-10 oocysts are sufficient to cause an infection. They can survive in the environment for months. The parasite is found throughout the world.