West Africa is struggling with the worst Ebola outbreak on record that has killed at least 4,950 people. Two nurses in the United States and one nurse in Spain have contracted Ebola outside of Africa but survived. 

The following are some facts about the outbreak:

Ebola has killed 4,950 people out of 13,241 confirmed, probable and suspected cases, almost all in Liberia, Sierra Leone and Guinea, according to the U.N.'s World Health Organization. It says the true death toll may be three times as much or 15,000 people, while the death rate is thought to be about 70 percent of all cases.

Ebola emerged in a remote forest region of Guinea in March and has also turned up in Nigeria, Senegal and Mali. Health officials declared Nigeria and Senegal Ebola-free in October.

There is no vaccine or cure for Ebola, a hemorrhagic fever. In past outbreaks, fatality rates have reached up to 90 percent. Ebola causes fever, flu-like pains, bleeding, vomiting and diarrhea.

Pharmaceutical companies are working on experimental Ebola vaccines and antiviral drugs, but a significant number of doses will not be available until at least the first quarter of 2015.

Ebola is not airborne. It is transmitted through blood, vomit, diarrhea and other bodily fluids. Healthcare workers in West Africa have been among the hardest hit by the outbreak.

Ebola symptoms generally appear between two and 21 days after infection, meaning there is a significant window during which an infected person can escape detection, allowing them to travel. However, they are not considered contagious until they start showing symptoms.

Recovery from Ebola depends on the patient’s immune response. People who recover from Ebola infection develop antibodies that last for at least 10 years.

Ebola patients have been treated in the United States, Spain, Germany, France, Norway and the United Kingdom.

The U.S. Centers for Disease Control and Prevention (CDC) has estimated that the number of infections could rise to up to 1.4 million people by early next year without a massive global intervention to contain the virus.

The United States, Britain, France, China, Cuba and international organizations are pouring funds, supplies and personnel into the affected parts of West Africa.

Ebola's suspected origin is forest bats. The virus was first identified in 1976 in what is now known as Democratic Republic of the Congo.