For those who don't know and just think this is some weird and backwards practice let me give you a quick laymen rundown of what an autoimmune disease is, and how this is supposed to work.
To put it as simple as possible, an autoimmune disease is when your body start to attack itself. Honestly this can happen for any number of reasons but one major theory for why they are so prevalent in first world countries is because we are too clean.
The human body has evolved for thousands of years to resist all of the germs and parasites that it would have to deal with, that got picked up as you go through life. Everything from hookworms, to tapeworms, to all sorts of viruses and bacteria. But, only in the past couple of hundred years have we been clean enough to fight off almost all of those.
And while that's a good, we don't get sick as much and we live longer, some people's bodies are having a harder tie adjusting. From an evolutionary standpoint 200 years might as well be the blink of an eye after all. So the body gets "bored" in a sense (in much the same way a bored child gets destructive) and it start to attack any benign source that causes it any slight irritation. With allergies it's the allergen itself that the body is reacting too, in crohn's disease it's food, bacteria, and even the lining itself of the intestines.
By inoculating himself with mostly benign hookworms, it'll give that regions immune system "something to do" in a sense (handing that child a video game to keep em busy). Seeing the hookworms as a bigger threat the immune system will start to attack those, and in theory relieve him of most, and in a few cases all, of his symptoms.
