I vaguely recall reading something on Usenet or something that would have made it onto Slashdot or Plastic in the late 90s/early 00s, where someone treated their allergies or asthma or something by deliberately infecting themselves with a parasitic worm---I forget which, maybe hookworm. They actually went to so far as to cultivate the worm in some medium that they could apply to their stomach using a custom-made patch, started pooping oocytes, and then completed the usual treatment course for whatever it was they infected themselves with. I can't recall if it cleared up the condition from which they were suffering, and obviously, this wasn't any kind of controlled trial. Lord knows that such a study would give an IRB six fits, and rightly so!