Both Cryptosporidium and Giardia Lamplia are cysts found in the intestins of warm blooded animals, cas, dogs, birds, cows, beavers, deer and sheep. And both are very resistant to chemical disinfection such as iodine and or chlorine. Just about the only way to rid these from water is filtration or boiling the water for 5 min. Only about 1/3 of the people who ingest these will show symptoms, but after about 2 days those 1/3 will leave their hunt for a hospital.
Symptoms of infection include (in order of frequency) diarrhea, malaise, excessive gas (often flatulence or a foul or sulphuric-tasting belch, which has been known to be so nauseating in taste that it can cause the infected person to vomit), steatorrhoea (pale, foul smelling, greasy stools), epigastric pain, bloating, nausea, diminished interest in food, It usually causes "explosive diarrhea" and while unpleasant, is not fatal.