Giardia is a small bacteria or parasite or whatever, that can contaminate humans and animals through water, food and direct contact to infected people/animals. It is especially prevalent in countries with not much hygiene or clean water. The water in Peru and Bolivia seems clean enough - but still we have always either purified the water with pills or boiled it. But with the food, we haven't been so careful, and we have ofcourse shaken many people's hands and patted dogs and cats (or that was just me - Andrés knows better ;-). Moreover, soap is never found in public toilets or in most hostels, and so on. And I wonder how much it is used after going to the toilet... But I guess people here would have stronger immune systems than someone from a country of hysteric hygeinic rules that forces shops to throw good food away and is the only place in the world where eggs are refrigerated from it pops out of the hen's butt till it hits the frying pan.
So for a few weeks now I have been sick in the stomach, on and off, with alternating constipation and diarrhea. And the last few days also fatigue, where it's been a whole mountaineering exercise for me climbing some stairs or walking up a small hill. It's not certain I have Giardiasis, but next week I'll probably buy the medicine against it anyway.
Because I know the symptoms from previous experience! When I was in Cambodia about 8 years ago I got Giardiasis over several periods, even though I was on medication several times. I guess patting the dogs, playing with the kids and giving them swimming lessons in the mud pond didn't help much to avoid it. And the side effects have been with me since, as a constant souvenir from my time there. Ever since my time in Cambodia I've been struggling with irritable bowel syndrome. My mum made me go to the doctor and ask if I still could have Giardia. I could hardly make myself ask the doctor because I thought they would think it was stupid, especially if I said I had read about Giardia persisting for years, on the internet - because it seems like doctors don't like it when you talk about things from the internet. But so many websites and online forums mention cases with people getting irritable bowel syndrome after having Giardiasis. And so many people write about their doctors waving their persisting symptoms off with stress, bad lifestyle and so on, without taking tests. But even the tests seem to be quite precarious in proving Giardia as it only sometimes shows positive, even though the victim has it in him or her. I'm sorry for saying this but sometimes doctors don't seem to give a shit about taking the time to study about or think about the causes their patients might have to their symptoms, and just tell them some common cause like stress.
Here's a link to a study from Bergen University that concluded the existence of chronic conditions such as irritable bowel syndrome or chronic fatigue, years after patients had Giardiasis:
http://cid.oxfordjournals.org/content/early/2014/08/12/cid.ciu629.abstract