What is Ebola? A breakdown of the outbreak

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(PIX11) -- At least one American aid worker is battling Ebola -- a severe, often fatal disease -- as West Africa grapples with an unprecedented outbreak.

Little threat is posted to the U.S. by the virus, which was first discovered in 1976 and can infect humans, monkeys, gorillas and chimpanzees, federal health officials say.

Below is a breakdown of Ebola, according to the Centers for Disease Control and Prevention:

What is Ebola?

It is one of several viral hemorrhagic fevers. There are five known subspecies of Ebolavirus, four of which cause illness in humans: Ebola virus (Zaire ebolavirus); Sudan virus (Sudan ebolavirus); Taï Forest virus (Taï Forest ebolavirus, formerly Côte d’Ivoire ebolavirus); and Bundibugyo virus (Bundibugyo ebolavirus). The fifth, Reston virus (Reston ebolavirus), has caused disease in nonhuman primates, but not in humans.

It’s still unclear from where the virus originates, but health officials think it’s likely animal-borne, with bats being the most likely host.

How is Ebola transmitted?

The virus spreads through direct contact with the blood, saliva or other bodily secretions of an infected person who is exhibiting symptoms. It is not transmitted through the air, food or water.

What are the symptoms?

Symptoms of Ebola may appear between 2 and 21 days after exposure to the virus, with a common incubation period of 8 to 10 days. Symptoms include fever, headache, joint and muscle aches, weakness, diarrhea, vomiting, stomach pain, lack of appetite, and abnormal bleeding.

How it Ebola treated?

Experimental treatments have been successfully tested in animals, but not yet on humans, so treatment of Ebola is still limited to “supportive therapy.” That means, patients who have or are believed to have contracted the virus are first isolated, then their fluids and electrolytes are balanced, their oxygen and blood pressure maintained and they are treated for any infections that would complicate their battle against the virus.

How many cases are there in this outbreak?

About 1,323 confirmed cases of Ebola has been found in Guinea, Liberia and Sierra Leone since March 2014. Of those patients, 729 have died -- about a 55 percent fatality rate, according to the World Health Organization.

Can I visit the affected region during the outbreak?

Issuing a Level 3 travel alert, the CDC is encouraging U.S. citizens against unnecessary travel to Guinea, Liberia and Sierra Leone. The agency says it is concerned travelers may not have access to health care facilities in those countries should they need them.

For the latest updates and travel notices related to the outbreak, visit the CDC’s website, here.