I believe we are predisposed to MS and there is something that triggers it. I had mono and chicken pox but I also had rosiola and feel those illnesses helped trigger my MS. My first MS sypmtoms happened right after going through a very serious stressful situation as a teenager. So because I experienced those illnesses and went through that stressful period, my MS was triggered. Snce MS is different for every single person who has it, I think different things trigger each case of MS.