There is some indication that parasites [hook and whip worms] may help in some auto-immune diseases. Most of the Google hits I get refer to Crohn's disease or MS, and a few others.
I am looking for information specific to Rheumatoid Arthritis.
Epidemiology references I have read [very few, but enough] lead me to believe that RA and similar diseases are much less prevalent in 3rd world countries, where more are infected with some form of parasite. There are a few web sites selling several species of helminthic parasites, but I see no information that they are helpful with RA.
