The Ebola outbreak in West Africa is now the deadliest ever

Editor's Note: This story has been updated to reflect the most current information about the outbreak. It was originally published in April. 

The deadliest Ebola outbreak in history has now killed at least 660 people in West Africa.

More than 1,000 cases have been reported in Guinea, Sierra Leone and Liberia since symptoms were first detected in the region four months ago.

The death of a Liberian man hospitalized in Lagos with the virus is raising fears that the latest outbreak could spread into Nigeria, Africa's most populous country. One of Liberia's most prominent doctors has also died from the virus, and an American doctor and aid worker are now infected.

Doctors Without Borders said the way the virus has spread is unlike any previous Ebola outbreaks, raising alarm among health workers.

"Ebola is usually a localized, rural disease, but this outbreak has a broad geographic spread and is reaching cities too," wrote GlobalPost Senior Correspondent Tristan McConnell, who is based in Nairobi, Kenya.

More from GlobalPost: Why we should all be very afraid of the unprecedented Ebola outbreak in Guinea

First detected in 1976, the Ebola virus has killed an estimated 1,900 people in the years since. Here are the seven deadliest Ebola outbreaks in history, according to figures from the World Health Organization and the Centers for Disease Control and Prevention.

1. Guinea, Sierra Leone and Liberia, 2014 (660 deaths)

(ZOOM DOSSO AFP/Getty Images)

2. Democratic Republic of the Congo (then Zaire), 1976 (280 deaths)

(CDC/Dr. Lyle Conrad)

3. Democratic Republic of the Congo, 1995 (250 deaths)

(CHRISTOPHE SIMON AFP/Getty Images)

4. Uganda, 2000 (224 deaths)

(CARLOS PALMA AFP/Getty Images)

5. Democratic Republic of the Congo, 2007 (187 deaths)

(AFP/Getty Images)

6. Sudan, 1976 (151 deaths)

(CDC/Dr. Lyle Conrad)

7. Republic of Congo, 2003 (128 deaths)

(DESIREY MINKOH AFP/Getty Images)