December 2013: Patient zero.
On Dec. 6, 2013, a two-year-old girl died in the Guinea region of Guéckédou after experiencing Ebola-like symptoms, according to a study in NEJM. Guéckédou sits at the intersection of Guinea, Liberia, and Sierra Leone.
Researchers identified the child after visiting the village, interviewing residents and analyzing hospital records in an attempt to trace Ebola from its first case. Although researchers do not know how the toddler became infected, it may have been through an animal, World Health Organization (WHO) officials said after the study was published.
January 2014: The virus spreads to the child's family.
By January, the child's sister, mother, and grandmother have all died after experiencing Ebola-like symptoms.
February 2014: Health worker spreads virus.
According to NEJM, a "health care worker from Guéckédou with suspected disease" traveled to nearby Macenta, Nzérékoré, and Kissidougou, which appeared to have triggered outbreaks there.
March 2014: 122 cases.
In early March, Guinea's Ministry of Health notifies its local Doctors Without Borders that the country is experiencing clusters of Ebola.
By the end of March, health officials in Guinea, Sierra Leone, and Liberia reported 122 cases of the virus.
Unlike past outbreaks, officials say this outbreak has been able to "jump" and evade health workers' containment efforts because travel within African countries has become easier. The virus would infect an entire village and then suddenly appear in a handful of people in a metropolitan city hundreds of miles away.
Moreover, the outbreak's epicenter is in West Africa, unlike past outbreaks, which largely occurred in Central Africa. West African governments are not as well-equipped to identify and respond to an Ebola outbreak as their Central African neighbors, officials say.
June 2014: 759 cases.
By the end of June, 759 cases had been reported in Guinea, Liberia, and Sierra Leone, including 467 deaths.
July 2014: 1,323 cases.
Despite increased efforts to stop it, the virus began spreading from locals to the men and women caring for them, claiming the life of one of Liberia's top doctors and infecting a U.S. physician and a medical missionary with Samaritan's Purse.
August 2014: 1,603 cases.
As of Aug. 1, there were 1,603 confirmed cases of Ebola and 887 confirmed deaths in four West African nations.
In August, two Ebola-stricken medical volunteers were airlifted to Emory University Hospital. They both recovered and were released on Aug. 21.
By Aug. 16, there were 2,252 confirmed cases in West Africa and 1,244 deaths.
During August, U.S. hospitals began reporting Ebola scares, beginning with a patient at Carolinas Medical Center in North Carolina. Before the end of the month, more than 60 hospitals reported some type of scare to the CDC, but none of the tests sent to agency returned positive for the virus.
September 2014: 3,685 cases.
On Aug. 31, WHO reported at least 3,685 confirmed cases of Ebola and 1,841 deaths.
By Sept. 14, at least 5,347 people had been infected with the deadly virus and 2,630 people had died.
In early September, the United Nations and Doctors Without Borders made an appeal for international aid saying that the "overwhelming" nature of the outbreak requires an overwhelming response.
President Obama on Sept. 16 announced that 3,000 U.S. military personnel will be deployed to West Africa with the intent to coordinate U.S. and international aid efforts through one command center, build treatment facilities, and provide training to local health workers and communities. The effort is called "Operation United Assistance."
October 2014: 7,470 cases.
As of Oct. 1, there were 7,470 cases of Ebola and 3,431 deaths.
On Tuesday, Sept. 30, a Dallas hospital announced that a Liberian man, Thomas Eric Duncan, tested positive for Ebola at the facility. This made his the first case diagnosed outside of West Africa. He died from the virus on Oct. 8.
On Oct. 13, the Dallas hospital announced that a nurse who cared for Duncan, Nina Pham, tested positive for Ebola—making her the first U.S. Ebola transmission. On Oct. 15, the hospital announced that a second nurse, Amber Vinson, also tested positive.
According to an Oct. 15 report, 8,997 people in seven countries have been infected and 4,493 have died as a result.