For anyone who doesn't know, hookworms are parasitic worms which inhabit the GI tract (instestines I think) of their host. They latch onto the intestinal walls and feed on the hosts blood. If infected by large quantities of them, it can cause major problems such as anemia due to blood loss but when infected by a small number of them, these adverse effects are barely noticeable. Allergic reactions are one of the bodies defense mechanisms against multicellular parasites like these and its believed that roundworms have an adaptation that partially weakens the immune system of the host in order to circumvent allergic reactions. As a result, controlled hookworm infection is used as a treatment for chronic allergy sufferers. Being a chronic allergy sufferer myself, I'm interested in this. The idea of having parasitic worms living in my GI tract is one thing that has always bothered me but considering roundworms are very small, not like a tapeworm (the thought of having one of those in my GI tract sends shivers down my spine) and the fact its only a very small number of them, I don't mind. Do these things weaken the immune system in general or is it just when it comes to allergies? I'd prefer to live with some allergies than become prone to sickness due to a weakened immune system.