I think there are a few factors.. Being exposed to what ever virus.. Then having vitamin D deficiency and then some genetic predisposition on top of it

this is copied & pasted from webmd.com:
How It Spreads

The virus is found in saliva, so you can catch mono from kissing someone who’s infected. You can also get it from drinking from the same glass or using an infected person's toothbrush. It's also found in blood and semen, so it's possible to get mono from sex, a blood transfusion, or an organ transplant.

You don't have to be sick to pass the virus to someone else. EBV stays in your body long after you get over mono. The virus can become active again months or years later, making you contagious once more.

also:
Other Diseases Caused by EBV

EBV is best known for causing mononucleosis, but less often it can lead to other diseases, including:

Ear infections and diarrhea in children

Guillain-Barre syndrome

Certain cancers, including Burkitt's lymphoma and cancers of the nose and throat

Studies also show a link between EBV and multiple sclerosis (MS), but more research is needed to determine if the virus can lead to MS.

pretty interesting stuffs. my fiance has been diagnosed w CEBV for over 20 years, now I have MS.. hhmmm

Interesting thread, I understand that this virus causes what is known as Glandular Fever in the UK, and I had Glandular Fever as a young teenager. I mentioned it to the neurologist but she didn't think it had much to do with MS!

I was 1st diagnosed with Epstein-Barr 3 years before. But it never went away. My husband asked my Dr. to check for MS.

I had the evb and infectious mono when I was 14. I didn't get diagnosed with ms till I was 49. Also have some other issues that correlate with this ms crap. At my Neuro office a guy that works there they call the ms guru and I've also had quite a few surgeries. He said I've probable been misdiagnosed and have had ms for 20+ years. The evb and mono deal are what are puzzling to me. Makes me wonder