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 Coverage on WebMD|
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.
She was one of two nurses at Texas Health Presbyterian Hospital who caught Ebola after treating Duncan. The second, Amber Vinson, 29, also recovered after being treated at Atlanta’s Emory University Hospital.
Duncan arrived in the U.S. on Sept. 20, 2014, to visit relatives. Ten days later, he became the first person to be diagnosed with Ebola in the U.S. He died Oct. 8, 2014.
In November 2014, a surgeon from Sierra Leone who lives in the United States died after being flown to the Nebraska Medical Center for treatment. Martin Salia, who was reportedly working at a hospital in the Sierra Leone capital of Freetown, arrived in the U.S. Nov. 15 and was taken to the medical center.
He was in extremely critical condition, suffering from kidney and respiratory failure, when he arrived, the hospital said. “We used every possible treatment available to give Dr. Salia every possible opportunity for survival,” said Phil Smith, MD, medical director of the hospital’s biocontainment unit. That included giving him the experimental treatment ZMapp, also given to other Ebola patients, according to the hospital.
But Salia’s disease was “extremely advanced,” Smith said in a statement.
Salia was reportedly a permanent U.S. resident who lived in Maryland with his family. Two other Americans -- Rick Sacra, MD, and cameraman Ashoka Mukpo -- recovered from Ebola after being treated in the Omaha isolation unit.
Craig Spencer, MD, a Doctors Without Borders physician who returned to the U.S. after treating Ebola patients in Guinea, was also diagnosed with the disease. He recovered after getting treatment at New York’s Bellevue Hospital in November 2014.
In total, six Americans infected with the virus in Africa have been brought back to the U.S. for treatment. All six, including aid workers Kent Brantly, MD, and Nancy Writebol, have recovered.
The fourth person was flown back to the U.S. in September 2014 for treatment at Atlanta’s Emory University Hospital, where Brantly and Writebol were also treated. This person's arrival came after the WHO said one of its doctors was being evacuated from Sierra Leone after getting Ebola. The man was released from the hospital in October 2014. The hospital said at the time he wanted to remain anonymous.
But a New England Journal of Medicine case report on the doctor, published May 7, 2015, identified him as Ian Crozier, MD, 43, an infectious disease specialist. The case report said that during his recovery, Crozier got severe uveitis, an inflammation of the middle layer of the eye that has many blood vessels.
Doctors found Crozier had Ebola virus in the clear fluid between his eye lens and cornea. They spotted it 10 weeks after the virus was no longer detectable in his blood. The case study suggested other Ebola survivors could be at risk of uveitis, too.
Ebola: Frequently Asked Questions
In fall 2014, President Barack Obama announced a plan to scale up the nation’s response to the Ebola crisis in West Africa. The Department of Defense sent personnel to Liberia to boost the international response and also planned to build units to treat Ebola patients.
Ebola was first identified in 1976, when it appeared in outbreaks in Sudan and the Democratic Republic of the Congo. It is named for the Ebola River, which runs near the Congolese village where one of the first outbreaks happened.
WebMD asked Amesh Adalja, MD, about the virus and efforts to contain it. Adalja is an infectious disease doctor at the University of Pittsburgh.
Q. How deadly is Ebola?
A. The Ebola strain in the current outbreak is the most lethal of the five known strains of the virus. It is called Ebola Zaire and usually kills up to 9 out of 10 infected people. But the high death rate might be due to a lack of modern medical care, Adalja says. “It’s hard to say exactly what the [death] rate would be in a modern hospital with all of its intensive care units.”
The CDC said in July the Ebola death rate in the West African outbreak is about 6 in 10, rather than 9 in 10. That shows that early treatment efforts have been effective, says Stephan Monroe, deputy director of the National Center for Emerging and Zoonotic Infectious Diseases at the CDC.
On July 31, 2014, the CDC issued a travel advisory recommending against non-essential travel to Guinea, Liberia, and Sierra Leone. As of December 2015, those advisories were no longer in effect.
Q. What are the symptoms?
A. At first, the symptoms are like a bad case of the flu: high fever, muscle aches, headache, sore throat, and weakness. They are followed quickly by vomiting, diarrhea, and internal and external bleeding, which can spread the virus. The kidneys and liver begin to fail.
Ebola Zaire kills people quickly, typically 7 to 14 days after symptoms appear, Adalja says.
A person can have the virus but not show any symptoms for as long as 3 weeks, he says. People who survive can still have the virus in their system for weeks afterward.
The virus can persist in semen at least 9 months after symptoms appear, according to a study conducted by the WHO, the CDC and the Sierra Leone government. The study was called preliminary. "Until more is known, the more than 8,000 male Ebola survivors across the three countries (in West Africa) need appropriate education, counseling, and regular testing so they know whether Ebola virus persists in their semen" as well as measures they should take to prevent exposing sexual partners, the CDC says. "Until a male Ebola survivor's semen has twice tested negative, he should abstain from all types of sex or use condoms when engaging in sexual activity."
Q. How does the virus spread?
A. Ebola isn’t as contagious as more common viruses, such as colds, influenza, or measles, Adalja says. It spreads to people by close contact with skin and bodily fluids from infected animals, such as fruit bats and monkeys. Then it spreads from person to person the same way.
“The key message is to minimize bodily fluid exposures,” Adalja says.
Q. What precautions should people take if they’re concerned they might come in contact with someone infected with Ebola?
A. “Ebola is very hard to catch,” Adalja emphasizes. Infected people are contagious only after symptoms appear, by which time close contacts, such as health care workers and family members, would use “universal precautions.” That's an infection control approach in which all blood and certain body fluids are treated as if they are infectious for diseases that can be borne in them, Adalja says.
Even though the virus can be transmitted by kissing or sex, people with Ebola symptoms are so sick that they’re not typically taking part in those behaviors, he says.
Q. Is there a cure or a vaccine to protect against it?
A. No, but scientists are working on both. Testing of several Ebola vaccines is underway in various locations.
There is no specific treatment for Ebola. The only treatments available are supportive kinds, such as IV fluids and medications to level out blood pressure, a breathing machine, and transfusions, Adalja says.
ZMapp was given to Brantly and Writebol, among others. But health officials don't know if it aided in their recovery. A trial of ZMapp in 18 Ebola-infected rhesus monkeys prompted recovery in all 18, researchers reported.
Sacra received a different treatment, called TKM-Ebola. He also received a blood transfusion from Brantly, a friend. Health officials don't know if any of these treatments helped with his recovery.
Duncan and Mukpo both received an experimental drug named brincidofovir. The drug is being tested for effectiveness against cytomegalovirus and adenovirus, but test-tube experiments done at the CDC and National Institutes of Health reveal it showed effectiveness against Ebola, according to its manufacturer, Chimerix Inc.
Mukpo and Pham also received blood transfusions from Brantly.
Spencer was reportedly given a range of treatments, including an experimental drug and a blood transfusion from Writebol. The experimental drug was not identified.
Q. Why do some people survive the virus?
A. That’s hard to say. Adalja thinks several things might play a role, such as a person's age and genetic makeup, and whether they have other medical conditions. Those aren't proven reasons, though.
Q. How can the outbreak be stopped?
A. Simple steps to control infection, such as gowns, gloves, and eye protection, can help halt the spread of Ebola, Adalja says. Public health officials will have to wait 6 weeks after the last case is reported before declaring the outbreak over, he says.
Keys to stopping Ebola include identifying patients; providing treatment, preventing the spread, and protecting health care workers, including following patients’ contacts and monitoring them for symptoms; and preventing future cases through education and urging people to avoid close contact with sick people or bodies, Frieden has said.
But, he said, turning the tide in Western Africa is “not going to be quick or easy. Even in a best-case scenario, it would take 3 to 6 months or more.”
Q. Could an Ebola outbreak happen in the United States?
Although concerns have grown since September 2014, when the first case was diagnosed in the U.S., health officials have continued to say they are well-prepared to deal with Ebola, and that the risk of an outbreak remains low.
“I have no doubt that we will control this importation or this case of Ebola so that it doesn’t spread widely in this country,” Frieden told reporters.
Because the virus isn't airborne, “it would take very close contact with someone who is at an advanced stage of illness to become infected,” Thomas Geisbert,a professor of microbiology and immunology at the University of Texas Medical Branch, tells HealthDay. Geisbert has been studying the Ebola virus since 1988.
One of the five Ebola virus strains caused an outbreak in laboratory monkeys in Reston, VA, outside Washington, DC, in 1989. People who were exposed to that strain of Ebola virus did not get sick, but they developed antibodies to it.