I wasn't aware of that Jim so you taught me something today. The Red Cross does say wait 12 months after visiting a country listed by the CDC as a malaria area before donating. They do not test blood for malaria so they rely on people being honest and aware of their travels. Frankly I was surprised the Quintana Roo state of Mexico is on the list - not as a major malaria locale but one where it is possible. Belize? Not surprised.
You can see if an area you are going to visit is listed as a malaria area by going here