Countries with a high probability of a particular disease are called endemic. This is due to the nature of the area and the way of life of the local population. You will not be able to donate for a certain period of time after returning from such a country. The duration depends on the country and the type of disease found there.
In countries affected by malaria, the refusal to donate blood can be longer than 6 months.
See endemic countries and time limits for refusal to donate blood below.