"Type 1 diabetes results from a breakdown of tolerance toward one’s own tissues—in this case, the insulin-producing islet cells of the pancreas—and their subsequent destruction. As part of their survival mechanisms, parasites suppress the host immune system. At the cellular level, they induce a range of anti-inflammatory cells and proteins in your body. This strong anti-inflammatory signal may nudge the immune milieu toward tolerance, preventing the cascade of events that leads to autoimmune diabetes. The hope is that the attack on islet cells will never materialize."
Can parasites prevent autoimmune diabetes? - Human Food Project