I can't explain the differences. It can be genetic, the food, more or less toxins in the environment or even the way people live and react to life. Portuguese don't easily get stressed about life pressures, in a certain way it's good but on the other end the society is disorganised, people are often careless and unprofessional. For me it's quite hard to live here because I'm certainly not like that. In my opinion if you are careless you have less stress and maybe less cortisol imbalances so if XMRV can be activated by stress maybe it gets less activated here. I lived in three other European countries and I know that the food habits are often very different. The diet of a Dutch or a Belgian is quite different from a Mediterranean diet. I don't know what else can be, as I said it's just my impression from living here. There are no studies so it's all impressions or speculations. How I became ill? that is the million dollar question. I was working very hard, I was doing a PhD. Just before I got ill I had a vaccination, I suspect a link there but I can't be sure. I ate healthy and did a lot of sports and I was happy. I find that I fit very well in the XMRV description (or with the little we know about it..) but I haven't been tested yet.