FAQ: The Deadly Ebola Virus
Editor's note: This story was updated on Dec. 29, 2015, with the WHO declaring an end to the spread of Ebola in Guinea.
April 4, 2014 -- Perhaps no virus strikes as much fear in people as Ebola, the cause of a deadly outbreak in West Africa.
The World Health Organization (WHO) reported more than 28,600 confirmed or suspected cases of the disease through Dec. 23, 2015. More than 11,300 people have died in the largest outbreak ever recorded.
The majority of cases were in the three West African nations of Guinea, Liberia, and Sierra Leone.
On Dec. 29, 2015, the WHO said Guinea -- where the epidemic began in December 2013 -- had ended its outbreak. The announcement came after tests showed for a second time that the last person known to have the virus had recovered. The country will have a 90-day "enhanced surveillance period" to spot any new cases as soon as possible.
Sierra Leone's outbreak was declared over in November 2015, pending the 90-day surveillance period. Liberia was declared in the clear in May 2015 and September 2015, but the disease re-emerged twice. The WHO is set to announce that Liberia is safe from the spread of the virus again in January 2016 if no new cases show up.
Ebola in the U.S.
An infected U.S. health care worker arrived March 13, 2014, at the National Institutes of Health Clinical Center in Bethesda, MD, for treatment, the NIH said in a statement. The person, who was not identified, caught the virus while working as a volunteer at an Ebola treatment center in Sierra Leone, the NIH said.
The health care worker, who at one point was in critical condition, was released from the clinical center on April 9, 2014, the NIH said in a statement.
No further information was released about the health care worker, who was the second American to be treated at the NIH facility. The first was Nina Pham, 26, a Dallas nurse who caught Ebola after treating Thomas Eric Duncan, a Liberian man who later died. Pham recovered from the virus.