Very interesting article. I wonder if some people are more susceptible than others, and less likely to recover spontaneously from Giardia infection - thinking of myself here, of course, at least in the latter category. I am reasonably sure I had it once in Nepal, and it disappeared very quickly after over a week when I took a dose of Tiniba (mentioned in the article). My SO has had it a few times (also mostly acquired in Nepal), and is so familiar with the accompanying symptoms that he was able to diagnose it in an acquaintance by, ahem, the smell of the guy's farts.