The world's second-biggest Ebola outbreak is still raging. Here's why.

SOURCE: National Geographic

An Ebola epidemic thundering through heavily populated provinces in the northeastern Democratic Republic of the Congo has sickened more than 110 people in the past week—despite the efforts of specialist medical teams, an effective vaccine, and new treatments that are being tested in the region.

The outbreak already is the second-largest on record, behind the epidemic that burned through West Africa from 2014 to 2016, killing more than 11,300 people. The World Health Organization has reported 1,290 cases of the Ebola virus disease in the recent outbreak, and as many as 833 deaths in North Kivu, a province bordering Rwanda and Uganda in the eastern DRC.

In its most extreme form, the viral hemorrhagic fever leads to uncontrollable bleeding and death.