Global health authorities are struggling to contain the world's worst Ebola epidemic since the disease was identified in 1976. The virus has killed at least 4,950 people.

Here is a timeline of the outbreak:

March 22: Guinea confirms a hemorrhagic fever that killed more than 50 people is Ebola.

March 30: Liberia reports two cases; Ebola suspected in Sierra Leone.

April 1: Medical charity Medecins Sans Frontieres (MSF) warns the epidemic's spread is "unprecedented." A World Health Organization (WHO) spokesman calls it "relatively small still."

April 4: Mob attacks Ebola treatment center in Guinea. Healthcare workers there and in Sierra Leone and Liberia face hostility from fearful, suspicious people.

May 26: WHO confirms first Ebola deaths in Sierra Leone.

June 17: Liberia reports Ebola in its capital, Monrovia.

June 23: With deaths above 350, making the West Africa outbreak the worst on record, MSF says it is "out of control," calls for massive resources.

July 25: Nigeria confirms its first Ebola case, a man who died in Lagos after traveling from Monrovia.

July 29: Dr. Sheik Umar Khan, who was leading Sierra Leone's fight against the epidemic, dies of Ebola.

July 30: Liberia shuts schools, quarantines worst-affected communities, using troops for enforcement.

Aug. 2: U.S. missionary physician infected with Ebola in Liberia is flown to Atlanta in the United States for treatment.

Aug. 5: Second U.S. missionary with Ebola is flown from Liberia to Atlanta for treatment.

Aug. 8: WHO declares Ebola epidemic an "international public health emergency."

Aug. 12: WHO says death toll tops 1,000, approves use of unproven drugs or vaccines.

Spanish priest with Ebola dies in Madrid hospital.

Aug. 15: MSF says epidemic will take about six months to control.

Aug. 20: Monrovia security forces fire shots, tear gas to disperse crowd trying to break out of quarantine, killing teen.

Aug. 21: Two U.S. missionary aid workers treated in Atlanta are released from hospital August 19 and 21 free of the virus.

Aug. 24: Democratic Republic of Congo declares Ebola outbreak, believed separate from West Africa epidemic.

Infected British medical worker is flown home from Sierra Leone for treatment.

Aug. 28: WHO puts death toll above 1,550, warns outbreak could infect more than 20,000.

Aug. 29: Senegal reports first confirmed Ebola case.

Sept 2: MSF president tells United Nations the world is losing battle to contain Ebola, slams "global inaction".

Sept. 3: Epidemic accelerates; deaths top 1,900. Officials cite close to 400 deaths in past week.

Third U.S. missionary doctor with Ebola is flown from Liberia for treatment in Omaha, Nebraska.

Sept. 5: Latest WHO tally: more than 2,100 dead out of about 4,000 people thought to have been infected.

Sept. 7: President Barack Obama says United States needs to do more to help prevent Ebola from becoming global crisis.

Sept. 8: Britain to send military and humanitarian experts to Sierra Leone to set up treatment center; United States to send field hospital to Liberia to care for health workers.

Fourth Ebola patient will be flown to United States for treatment in Atlanta.

Sept. 9: WHO says at least 2,296 dead out of 4,293 cases recorded in five countries.

Sept. 12: Cuba to send 165 doctors and nurses to Sierra Leone to treat Ebola patients.

Sept. 13: Liberia appeals to Obama for aid to fight Ebola.

Sept. 16: United States promises to send 3,000 military engineers and medical personnel to West Africa to build clinics and train healthcare workers.

WHO says 2,461 dead out of 4,985 infected, doubling death toll in past month.

Sept. 17: MSF says French nurse volunteer in Liberia has Ebola.

Sept. 18: WHO says 2,630 dead out of 5,357 thought infected.

United Nations special mission to combat Ebola will deploy staff in Liberia, Guinea, Sierra Leone. Security Council adopts resolution calling for lifting travel, border restrictions.

French President Francois Hollande says military hospital will be set up in Guinea.

Sept. 19: Streets in Sierra Leone's capital, Freetown, are deserted under three-day lockdown to try to halt Ebola's spread.

Sept. 20: Liberian Thomas Eric Duncan flies from Liberia to Dallas via Brussels and Washington after trying to help woman with Ebola in his home country.

Sept. 22: WHO says outbreak largely contained in Senegal and Nigeria; says Ebola has killed more than 2,811 in West Africa.

Sept. 23: U.S. Centers for Disease Control and Prevention (CDC) estimates between 550,000 and 1.4 million people in West Africa may have Ebola by January.

Sept. 25: Duncan goes to Dallas hospital with fever and abdominal pain. He is sent back to apartment where he is staying despite telling a nurse he traveled from West Africa.

Sept. 26: New WHO tally: 3,091 dead out of 6,574 probable, suspected and confirmed cases.

Cuba says will train 296 more doctors and nurses to treat West Africa Ebola patients, in addition to 165 already preparing to go to Sierra Leone.

Sept. 28: Duncan returns by ambulance to Dallas hospital.

Sept. 30: CDC confirms Duncan has Ebola; first case diagnosed in the United States.

Oct. 1: WHO says 3,338 dead out of 7,178 West Africa cases.

Cuba sends 165 doctors and nurses to Sierra Leone, the first group of volunteers from the Caribbean island.

Oct. 2: Britain pleads at conference in London for international help to fight epidemic.

NBC News says American freelance cameraman, Ashoka Mukpo, has Ebola; he will be flown to United States for treatment.

Oct. 3: WHO says 3,439 dead out of 7,492 suspected, probable and confirmed cases in West Africa and United States, which has one.

Ugandan doctor with Ebola arrives in Frankfurt from Sierra Leone for treatment.

Oct. 4: Volunteer nurse in Liberia who was first French national to contract Ebola leaves hospital outside Paris after being successfully treated.

Oct. 6: Spanish nurse is infected with Ebola; she treated infected Spanish priest who was repatriated to Madrid and died.

Cameraman Mukpo in Omaha; taken to Nebraska Medical Center.

Oct. 8: Duncan, the first person diagnosed with Ebola in the United States, dies in Dallas hospital.

U.S. government orders five major airports to screen passengers from West Africa for fever.

Oct. 9: WHO revises Ebola death toll to 3,865 out of 8,033 cases, says there is no evidence epidemic is being brought under control in West Africa.

Britain to screen passengers entering country through London's two main airports and Eurostar rail link with Europe.

Some lawmakers want United States to ban travelers from West African countries hit hardest by Ebola.

Oct. 10: WHO ups deaths to 4,033 out of 8,399 cases in seven countries. Most fatalities in Liberia, Sierra Leone and Guinea.

Oct. 11: New York's John F. Kennedy International Airport begins screening travelers from three West African countries for Ebola symptoms.

Oct. 12: Dallas nurse tests positive for Ebola, becoming first person to contract it in the United States. Nina Pham was infected while caring for Duncan.

Oct. 14: At Heathrow, London's busiest airport, Britain begins screening travelers from West Africa.

Sudanese U.N. medical official who contracted Ebola in Liberia dies in German hospital.

Oct. 15: Second Texas nurse who treated Duncan is diagnosed with Ebola. Amber Vinson will be treated at Atlanta's Emory University Hospital. Authorities say she took flight from Cleveland to Dallas/Fort Worth International Airport while running slight fever.

WHO raises death toll to 4,493 out of 8,997 cases; says epidemic still spreading in West Africa.

Oct. 16: U.S. congressional subcommittee sharply questions health officials about response to Ebola in United States.

U.S. National Institutes of Health says nurse Pham will be moved to NIH isolation unit in Bethesda, Maryland, from Dallas.

Oct. 17: WHO raises death toll to 4,546 out of 9,191 cases.

Senegal declared free of Ebola.

Obama appoints Ebola response coordinator.

Oct. 19: Nigeria declared free of Ebola.

Spanish nurse appears to be free of Ebola.

Oct. 20: In Texas, 43 people taken off Ebola watch lists.

United States issues stricter guidelines for health workers treating Ebola victims. No skin or hair exposed.

Oct. 21: Medicins Sans Frontieres says will start trials of experimental Ebola drugs at its treatment centers in West Africa next month.

Cuba sends 53 doctors and nurses to Liberia and 38 to Guinea to treat Ebola patients, the second group from that country.

U.S. says as of Oct. 22 travelers to the United States from Liberia, Sierra Leone and Guinea must fly into one of five designated airports for enhanced screening.

Oct. 22: United States will monitor for 21 days anyone entering the country from three nations at center of epidemic.

NBC freelance cameraman, Ashoka Mukpo, is declared free of Ebola; leaves hospital in Nebraska.

Oct. 23: New York City doctor Craig Spencer, who treated patients in Guinea, tests positive for Ebola.

Mali becomes sixth West African country hit by Ebola.

Oct. 24: Dallas nurse Pham is Ebola-free; leaves hospital.

New York and New Jersey order the quarantine of all medical workers returning from Ebola-hit West Africa countries. Nurse Kaci Hickox tests negative and is quarantined, under protest, for two days in New Jersey. She goes to Maine, where she is ordered isolated in her home. She challenges that order.

Oct. 25: WHO raises death toll to 4,922 out of 10,141 cases.

Illinois orders the quarantine of all high-risk travelers returning from Ebola-hit West Africa countries.

Oct. 26: Florida will monitor for 21 days people returning from Ebola-hit countries and quarantine "high-risk" individuals.

Oct. 27: U.S. Army begins isolating personnel returning from Ebola missions in West Africa.

Australia becomes first developed country to shut its borders to areas hardest hit by Ebola; bans visas for citizens of Sierra Leone, Liberia and Guinea.

Oct. 28: Dallas nurse Vinson is free of Ebola; leaves Emory University Hospital.

Oct. 29: Ebola appears to be slowing in Liberia, WHO says.

Quarantine-like monitoring expanded to all U.S. military personnel returning from Ebola relief efforts in West Africa.

California enacts 21-day quarantine of travelers who had contact with Ebola patients but policy more flexible than rules in New York, New Jersey and Maine.

Oct. 31: Canada stops issuing visas to people from Sierra Leone, Liberia and Guinea.

Nov. 3: Mali is thought to be Ebola free, but officials searching for 39 people who traveled on buses with toddler who died from virus.

Maine and nurse Hickox reach agreement allowing her to travel freely in public and not be quarantined at home.

Nov. 4: Asia not contributing enough to global effort to fight Ebola, World Bank Group President Jim Yong Kim says.

Nov. 5: WHO revises deaths downward for second week running, puts toll at 4,818 out of 13,042 cases as of Nov. 2. Says still seeing slowdown in weekly cases in Liberia, Guinea is stable, incidence of Ebola still rising in Sierra Leone.

President Obama will ask Congress for $6.2 billion in new funds in U.S. fiscal year to fight Ebola in West Africa and the United States, according to officials familiar with request.

China plans to send some 1,000 medical workers and experts to West Africa, state-run Xinhua news agency reports.

Australian Prime Minister Tony Abbott says his country will fund a treatment clinic in Sierra Leone, responding to pressure from the United States and others to do more.

Nov. 7: Death toll rises to 4,950 out of 13,241 cases in the three worst-hit countries of West Africa.

Dallas declared Ebola-free after first transmission within the United States.

Nov. 11: New York doctor Craig Spencer is Ebola free and leaves hospital.