fascinating story on WNYC, RadioLab (do a google search) about Parasites.. about one positive case, where a man cured his allergies & asthma by deliberately infecting himself with a hookworm. The theory is that hookworms evolved in harmony with humans having a modulatory effect on the immune system in exchange for food. He went to Africa solely for this purpose, to walk around in feces until he was infected...Upon returning no longer has asthma or allergies....too many hookworms will cause anemia however.. have a listen....
Replied by Robert Henry
Ten Mile, Tn Usa