I recently got giardia after a section hike from New York to Massachusetts.
I found a natural cure online that brought immediate relief and disappearance of all symptoms within 12 hours. It was on a web page on diagnose-me.com, and it said that 20-some number of people (I've had trouble finding the page again) with giardia took garlic on an empty stomach two hours before meals twice a day for three days and 100% of these people were symptom free after three days.
So I tried the same thing and got immediate relief from my ongoing severe stomach pains. All stomach pain and cramping were gone within 12 hours and did not reoccur. I chewed garlic cloves and washed it down with good purified water to make sure I got plenty of alacin, the curative property of garlic that is lost in many garlic pills. If you can find pills with a good dose of alacin in them, the article says those will work as well.
I have a theory that I'd like to run by those who've had giardia. The theory is that people a healthy and well-functioning digestive tract are not likely to get giardia and if they do it is not likely to cause serious distress nor is the giardia likely to survive long.
This theory is based partly on information I got from a hiker who'd had giardia whose doctor told him that giardia feeds on sugar and lots of people have giardia in their system, but it is often not a problem unless there is an imbalance like too much sugar consumption. This particular hiker's giardia became distressing and required treatment, he said, because he had come upon an ongoing source of free sugary cookies and consuming a lot of them prior to getting ill.
I started drinking water without treating it 8 days into my trail hike and noticed within a couple days that I had more gas than usual, but no diarrhea or stomach pains or any other distressing symptoms. I take probiotics daily, don't eat much sugar and probably have a fairly healthy digestive tract, maybe 6 or 7 on a scale where 10 is the healthiest. When I got off the trail I stayed with friends who offered me sugary baked goods for breakfast, and strawberry pie topped with gobs of whipped cream for lunch, all of which I consumed in large amounts. That night I woke up with stomach pains so bad I thought I was going to have to go to the emergency room. I think this distress was due to the sugar feeding the giardia. These severe pains persisted for two more days before I found the garlic cure online. A clove of garlic on an empty stomach two hours before dinner gave me instant relief; I had moderate stomach pain after dinner and complete disappearance of pain by morning. The pain has not recurred.
Does this theory match your experience?
Can you refine the theory to make it more accurate and descriptive?
Did you find an effective and helpful cure that you want to share?
Do you have time and interest to design a poll that may shed more light on this issue?

So, here's an initial poll:
Based on your own past experience with giardia, do you see a link between the existence/severity of giardia symptoms in your system and the excessive consumption of sugar or other unhealthy eating habits, lack of healthy bacteria in your system (perhaps due to consumption of antibiotic laden meat and dairy products), or other indicators or a less than healthy digestive system?
1) Yes, I can see a clear connection
2) I can see a possible connection
3) I'm uncertain
4) I don't see any connection
5) None of the above

Thanks.
Cheers.