Autoimmune causes: Reactive arthritis (Reiter's)
Autoimmune disease has a direct correlation to gut and mouth bacteria. I have taken Minocycline for years but only had damage when my old rheumatologist took me off for 5 years. Look at the Road Back Foundation website. I was in martial arts even with RA. My RA started from a bite when I was working on a 2Nd masters degree in special education.
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Reactive arthritis (Reiter's) can be triggered by Chlamydia. My celiac started 14 years ago after catching H1N1 followed by an attack on my life (stress is a big trigger). Pregnancy, other viral and bacterial infections, and of course genetics also factor in on causes.