Cryptosporidium is a type of coccidian protozoan parasite that can cause severe illness in both humans and animals. The parasite is commonly found in the intestines of vertebrates like sheep and cattle, where it multiplies rapidly and produces oocysts that are shed in their feces. These oocysts can contaminate soil, water, and food, and can remain infectious for long periods of time even in harsh environments.

When cryptosporidium oocysts enter public water supply systems, either through contaminated animal waste or human sewage, they can pose a serious health risk. If ingested, the parasite can cause diarrhea, stomach cramps, and dehydration, which can be particularly dangerous for people with weakened immune systems. Cryptosporidiosis outbreaks have been reported in many countries, and it is considered one of the leading causes of waterborne disease worldwide.