Regarding Giardia and crypto: Can one develop a tolerance or immunity to them? I remember drinking from streams as a child while fishing and hiking in the backcountry. Surely I couldn't have been lucky than many times.
Submitted by - -Lonnie J., Donkin, NS
The short answer is yes. Many people, as many as one out of every 10, can carry Giardia without ever knowing they are a carrier. Everyone seems to develop at least some immunity after a case of giardiasis.
With cryptosporidium the answer is less clear. Immunity does seem to develop in some people after exposure, but if those same people swallow enough of the pathogen later, they will probably get cryptosporidiosis again. You have to down more than a few to get sick, so, in fact, no matter your tolerance for both germs, if you drink enough of them, you may get the disease. You could have indeed been lucky.—Buck