Everything You Need to Know About Ebola
PHOTO: In this 2014 photo provided by the Samaritans Purse aid organization, Dr. Kent Brantly, left, treats an Ebola patient at the Samaritans Purse Ebola Case Management Center in Monrovia, Liberia.

Two Americans, including a doctor, are infected with the Ebola virus and Liberia's lead Ebola doctor recently died from the virus.

That news came amid a heavy toll -- 1,323 infected in the current outbreak as of July 31, according to the World Health Organization. Of those infected, 729 had died, meaning this outbreak has had a fatality rate of approximately 60 percent.

What Is Ebola?

The Ebola virus is described as a group of viruses that cause a deadly kind of hemorrhagic fever. The term "hemorrhagic fever" means it causes bleeding inside and outside the body.

The virus has a long incubation period of approximately eight to 21 days. Early symptoms include fever, muscle weakness, sore throat and headaches.

As the disease progresses, the virus can impair kidney and liver function and lead to external and internal bleeding. It’s one of the most deadly viruses on Earth with a fatality rate that can reach between approximately 50 to 90 percent. There is no cure.

How Is It Transmitted?

The virus is transmitted through contact with blood or secretions from an infected person, either directly or through contaminated surfaces, needles or medical equipment. A patient is not contagious until he or she starts showing signs of the disease.

Thankfully, the virus is not airborne, which means a person cannot get the disease simply by breathing the same air as an infected patient.

Where Are the Infected?

In this current outbreak, which started in March, people in three countries -- Sierra Leone, Liberia and Guinea -- have been infected after the outbreak began along a shared border.

This week officials reported an infected man may have put others at risk after flying on a commercial airliner from Liberia to Nigeria. The man later died in Nigeria, but the WHO has not yet reported any cases of people becoming infected in Nigeria.

Two Americans infected with the disease are scheduled to be evacuated to the U.S. by early next week.

Ebola-Stricken Doctor Takes 'Turn for the Worse'

What Would Happen if the Ebola Virus Landed in the US

Ebola Alert: 2 More Americans Quarantined During Outbreak

Where Did the Virus Come From?

The dangerous virus gets its name from the Ebola River in the Democratic Republic of Congo, which was near the site of one of the first outbreaks. The virus was first reported in 1976 in two almost simultaneous outbreaks in the Sudan and the Democratic Republic of Congo. They killed 151 and 280 people, respectively.

Certain bats living in tropical African forests are thought to be the natural hosts of the disease. The initial transmission of an outbreak usually results from a wild animal infecting a human, according to the WHO. Once the disease infects a person, it is easily transmissible between people in close contact.

Until this outbreak, approximately 2,361 people had been infected since the disease was identified in 1976. More than 1,548 of those infected died from it.

Who Is At Risk?

The virus is not airborne, which means those in close contact can be infected and are most at risk. A person sitting next to an infected person, even if they are contagious, is not extremely likely to be infected.

Health workers and caregivers of the sick are particularly at risk for the disease because they work in close contact with infected patients during the final stages of the disease when the virus can cause internal and external bleeding.

In this outbreak alone, more than 100 health workers have been infected and at least 50 of them have died, according to the WHO.

More ABC News