The world's second-largest Ebola outbreak on record is underway in the Democratic Republic of the Congo and has now spread to Uganda.
What to watch: The World Health Organization and aid groups are pouring resources into the region to try to contain it, but the longer this Ebola outbreak continues, the greater the likelihood it will spread to other highly populated areas within the country, move to other neighboring countries or even internationally.
Threat level: The danger of this particular outbreak, which began Aug. 1, 2018, is that it's what several experts call the "perfect storm" of a highly lethal and contagious virus in an area of the DRC that's a hub for poverty and neglect, insurgent activities, distrust of government and international organizations, and a mobile population with many refugees.
- This, plus violence directed at health-care workers, has stymied public health efforts to halt this outbreak.
Go deeper: Ebola treatment distrust leading to greater likelihood of spread