For many decades the Congo has had a lot of unsanitary bush meat hunting and food-prep practices, including a massive amount of primate consumption. That's the primary theory of how the Simian Immunodeficiency Virus made the jump from primate to human. West Africa also is having this problem with Ebola. You're right as far as the reservoir of sequences is "well prepared" by incubating in old world primate hosts. I don't know the story behind Zika or EVD.