How are bites infectious if CBI is a fungal infection? Fungal infections can't be transferred via bodily fluids.
How does the infection get to the brain? If it can't be introduced to the bloodstream via bodily fluid exchange, it therefor wouldn't have any avenue to get to the brain.
If the initial outbreak was caused by contaminated crops, the spores would end up in the stomach and intestines, while any spores breathed in would would go to the lungs. CBI would therefor instead be a stomach and/or lung infection rather than a brain infection.