In wrong order:
2. Bringing water to a boil takes care of bacteria and oocysts.
3. It's not clear how common it is. But from the CDC website:
"Cryptosporidiosis (krip-toe-spo-rid-e-o-sis), is a diarrheal disease caused by a microscopic parasite, Cryptosporidium parvum. It can live in the intestine of humans and animals and is passed in the stool of an infected person or animal. Both the disease and the parasite are also known as "Crypto." The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine disinfection. During the past two decades, Crypto has become recognized as one of the most common causes of waterborne disease (drinking and recreational) in humans in the United States. The parasite is found in every region of the United States and throughout the world."
1. Erm, it's the hard-shelled cyst (oocyst) from crytosporidium parvum (and I bet I've got that latin all snarled up as I'm not a biologist) Checkout the
CDC crypto site for more info.
And a bit more - we yakked about this off and on a while about. From what I have been able to dig up, many folks either are not susceptible to it or are have no illness from crytosporidosis infections. A further significant percentage of folks who do contract it fully recover with no ill effects. However, it clearly can be quite lethal - scores of folks died from it in at least 2 separate outbreaks in the US in the last 20 or so years.
HTH,
Tom