GWEN IFILL:

Next: As we have seen with recent pandemics, emerging diseases like Zika and Ebola can cross continents and oceans with uncontrolled speed.

Scientists are identifying areas where new infectious diseases are most likely to emerge, where there are high risks of animal viruses passing to humans. One of those areas is Southern China.

Hari Sreenivasan brings us this report, which was produced in collaboration with Global Health Frontiers.