The next Ebola will come from _____.

Influenza, Ebola, HIV — these viruses all made the jump from chickens, bats and chimpanzees to us. Most viruses that infect humans start this way. Some don't become contagious, but others —take the 1918 flu that killed at least 20 million people — rapidly spread across continents.

We asked four researchers where the next disease to threaten us might emerge from:

• Thumbi Mwangi, veterinarian, Washington State University: Control small diseases to be ready for big ones
• Anne Rimoin, epidemiologist, UCLA: Watch where people and animals interact
• Justin Lessler, epidemiologist, Johns Hopkins University: It's not where a virus comes from but how it becomes contagious
• Kevin Olival, ecologist, EcoHealth Alliance: There are 5,000 places to look