Here's What You Need to Know About the Largest Ebola Outbreak in History

The deadly Ebola virus continues to spread in West Africa, claiming a Liberian doctor among its more than 660 victims thus far and infecting two Americans in the country.

Here are some of the latest things you should know about the outbreak, which the World Health Organization says is largest in recorded history.

• The numbers, according to WHO: As of July 20, 1,093 people were infected with the Ebola virus in three countries, resulting in 660 deaths.

A breakdown of Ebola infections and deaths as of July 20, 2014. (Image source: WHO)

• Dr. Samuel Brisbane, a senior doctor at Liberia's largest hospital, died Saturday at an Ebola treatment center on the outskirts of the capital, Monrovia. He is the first Liberian doctor to die in the outbreak, the WHO said. Sierra Leone's top Ebola doctor fell ill with the disease last week, and the aid group Samaritan's Purse said Saturday that an American doctor in Liberia was also sick.

A picture taken on July 24, 2014 shows a staff member of the Christian charity Samaritan's Purse spraying product as he treats the premises outside the ELWA hospital in the Liberian capital Monrovia. An American doctor battling West Africa's Ebola epidemic has himself fallen sick with the disease in Liberia, Samaritan's Purse said on July 27. (AFP/ZOOM DOSSO)

• The first case and death in Nigeria from the virus occurred Friday in a Lagos hospital. The deceased man was identified as a Liberian government official with the finance ministry who arrived in the country Tuesday. He was isolated after displaying Ebola-like symptoms, which included fever, vomiting and diarrhea. After his death, Nigerian Health Minister Onyebuchi Chukwu said all ports of entry in the country are now on "red alert" and health officials are investigating all people who had contact with the deceased. This case is especially concerning because Lagos is considered a megacity with many living in cramped conditions, making the spread of a viral disease particularly concerning.

A man reads a newspaper with a headline announcing government efforts to screen for Ebola at a newsstand in Lagos on July 27, 2014. Nigeria was on alert against the possible spread of Ebola on July 27, a day after the first confirmed death from the virus in Lagos, Africa's biggest city and the country's financial capital. The health ministry said on July 25 that a 40-year-old Liberian man died at a private hospital in Lagos from the disease, which has now killed more than 650 people in four west African countries since January. (PIUS UTOMI EKPEI/AFP/Getty Images)

• Concern over air travel and the spread of Ebola was reignited after the Liberian official died in Nigeria, but also because he had a layover in the country of Togo, making it possible that the disease could have spread to a fifth country. This case shows that screening people as they enter the country could slow the spread of the disease it's not a guarantee that Ebola won't travel by air, according to Dr. Lance Plyler, who heads Ebola medical efforts in Liberia for aid organization Samaritan's Purse.

• An Ebola patient in Sierra Leon was taken from a treatment center by her family and died in an ambulance, according to Reuters. Distrust of modern medicine and a preference for traditional healing methods, health officials told the news source, is slowing the effort to stop the virus' spread. The New York Times also reported that some, fearing health workers are spreading the disease, are preventing aid from coming into or passing through their villages.

In a further effort to contain the disease going forward, Liberia's President Ellen Johnson Sirleaf closed some border crossings and ordered strict quarantines of communities affected by the outbreak. Last week, the president formed a new taskforce charged with containing the disease.

WHO also established the Sub-regional Outbreak Coordination Center in Conakry, Guinea, last week.

"The Center will allow monitoring in real-time of the activities to fight the epidemic, in collaboration with the national committees and the teams deployed on the ground," Dr. Luis Gomes Sambo, WHO regional director for Africa, said in a statement to the organization.

“The Center will act as a platform to consolidate and harmonize the technical support being provided to West African countries affected by the outbreak. It will also help to mobilize resources for the response,” Dr. Francis Kasolo, director for disease prevention and control for the WHO African Region, added.

The Ebola virus has a 90 percent fatality rate, according to WHO, and is spread from animals to humans and from humans to humans. There is no specific cure or vaccine for the disease.

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The Associated Press contributed to this report.