How Ebola Works

Ebola Breaks Out
A woman openly weeps outside the Doctors Without Borders Ebola treatment center in Monrovia, Liberia in 2014 while awaiting news on her husband, who was admitted with signs of the virus. John Moore/Getty Images

Despite all the fear around Ebola, not that many humans have actually died from the disease, relative to other known diseases. Between 2014 and 2016, in the 25 outbreaks that occurred, about 16,000 cases of humans infected with Ebola have been reported and about 6,500 of those cases have ended in death. (Note: More than 80 percent of the Ebola cases reported are attributed to the 2014 outbreak in West Africa.) [source: World Health Organization].

As we mentioned, Ebola is actually a family of five virus types. The two most deadly to humans are the Zaire and Sudan types. Not only do these have the highest fatality rates (60 to 90 percent for Zaire and 40 to 70 percent for Sudan), they've also appeared the most in the known outbreaks that have occurred [source: Feldmann].

After the initial appearances of both of these strands in 1976, the viruses hid for awhile. But when the Ebola family reappeared, it came back with a vengeance. Since the mid-'90s, both of these Ebola types have wreaked havoc on Africa every few years. Most of these outbreaks have been contained to central Africa quite close to the equator in countries like the Democratic Republic of Congo, Gabon and Uganda. In March 2014, however, the first outbreak of the Zaire strand was seen outside of this region in the western African country of Guinea, quickly spreading to nearby countries (Liberia, Sierra Leone, Mali, Senegal and Nigeria).

That year, a visitor from west Africa to the U.S. turned out to have Ebola, and two health care workers in Dallas who treated him tested positive for the disease. They both recovered. In addition, a medical aid worker who had volunteered in Guinea also was hospitalized in New York City, and was confirmed to have the disease. He also recovered [source: CDC].

Scientists worry that Ebola outbreaks have the potential to spread more rapidly, due to climate change. The latter's effect on the trees in Africa, which bats depend upon for food, may cause an increase in bat reproduction, or else compel the animals to roam to new areas. In addition, as droughts affect agricultural areas and force humans to go into the forest for food, they may be exposed more often to bats carrying the Ebola virus [source: Barnato].

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