How did the use of spanish missions affect the spread of disease in the americas ?

The Spanish were trading to different countries. For example, the Spanish would travel to the aztec or some other empire for trade. You give me bread, i give you supplies to build an army. So the spanish traded food and that person had a deadly diease and now it's on the food. The empire eats that food and now that empire becomes sick. Thats one of the biggest reasons that dieses spred, through trade, and missions because of traveling to other countries.