My father worked as a farmer and never had any health issues, but some auto immune disease attacked him and I am not sure how it happened. He was always very physically strong and in a good shape. The only thing that could possibly be the cause is the constant radiation. What kind of influence it has on the auto immune disease?
There is actually a great link between the radiation effect and the condition your father has. This connection has been proved, but still not explained. It is a fact that people that work outside in the open fields have a much higher risk to develop some skin changes (tumor) ad autoimmune disease.