A few years ago I sought help from an American Nurse who was also skilled in Ayurvedic Medicine

So, my exposure was in 1985 and 1986 in India and Nepal and possibly Thailand.

What she told me was interesting regarding my personal medical condition. She said that people who get giardia like they have in places like India and Nepal which is protozoas  in your intestines. It isn't usually fatal unless you starve to death or can't get enough protein (more than the protozoas eat in your intestines). So, it's not fatal usually like Amoebic dysentery can be.

However, you often get very skinny like I did for about 6 months which can throw off your metabolism in various ways including getting eventually hypothyroidism and in worse cases an autoimmune disorder. So, if you are a world traveler that has been to 3rd world nations where water or food pollution is more common and if you don't boil any water you drink for 5 minutes at least or someone who prepares food for you doesn't boil the water they are using for 5 minutes or more you can be exposed to giardia like I and 3 members of my family were in India and Nepal. After all, we were there about 4 months total so no matter how careful we were regarding any water or food we prepared everyone I knew who had been to Kathmandu, Nepal that year from the U.S. or Europe got giardia.