Medical workers with the nonprofit Doctors Without Borders treat a patient for Ebola in Gueckedou, Guinea. Despite their protective gear, the workers try to maintain human contact with patients by talking with them and getting close enough to look into their eyes.

Sylvain Cherkaoui/Cosmos Health workers have called the Ebola outbreak in West Africa unprecedented, overwhelming and even out of control.

With 844 cases so far, it's the largest and deadliest outbreak since the virus was discovered in 1976.

And it doesn't show signs of slowing down. On Tuesday, the World Health Organization reported 50 new cases in Liberia and Sierra Leone. Despite the current crisis, however, the likelihood of the virus's spreading beyond Africa is very low.

Here's what we know about this painful and deadly disease.

What is it? A nasty, often fatal form of hemorrhagic fever that gets its name from a river in the Democratic Republic of Congo. That's where Ebola was first detected, in a nearby village.

There are five different species of Ebola, each named after where it was first found. Sudan, Bundibugyo (named after a Ugandan district) and Zaire viruses have all been linked to outbreaks in Africa.

The Tai Forest virus, found in the Ivory Coast, has only caused one documented case — a scientist who caught it from sick chimpanzees in 1994.

The fifth species is Reston, named after the D.C. suburb of Reston, Va. Yes, that's right: Ebola was found in Virginia, but just in monkeys. They had been shipped from the Philippines to a Reston laboratory.

So far, there have been no documented outbreaks of Ebola Reston in humans.

Symptoms: It can take anywhere from two to 21 days after infection for symptoms to kick in, but once they do, the pain is excruciating.

It starts off with a fever, muscle pains, vomiting and diarrhea. It also makes the victims so weak that it leaves them bedridden. As the virus spreads, it can shut down major organs, such as the kidneys and liver.

And the infection can cause internal and external bleeding from openings in the body, including eyes, ears, nose, rectum and even pores. The peak of the illness is the first seven to 10 days, during which patients are most likely to die.

How often does it kill somebody? Each Ebola species is associated with a specific mortality rate.

Health workers are currently battling the deadliest one, Zaire, which can kill up to 90 percent of people infected.

So far in this outbreak, there have been 518 deaths. That puts the current mortality rate at about 60 percent.

This improvement is most likely because health workers are better at giving supportive care to patients, like nutrition and fluids, which may help their immune systems fight the virus. Health workers also track down those infected, or likely infected, more quickly. So supportive care can start earlier. How does it spread? Through close contact with infected blood, saliva, urine and stool.

In previous outbreaks, researchers have found that the virus initially spread to people from infected monkeys, which are hunted and eaten in parts of rural Central Africa. Some scientists also think that bats are the initial source of the virus.

Health care workers and family members can catch Ebola by caring for the sick. An infected person remains contagious even after death. So family members can also be infected while preparing a body for burial.

Where does it live? The illness mostly crops up in remote villages of Central Africa, with outbreaks in South Sudan, Democratic Republic of Congo and Gabon. There have also been outbreaks in Uganda in 2000, late 2007 and 2012.

This year marks the first Ebola outbreak in West Africa. The WHO reported the first confirmed cases in Guinea back in March, although some officials say people may have been infected in late 2013. The virus then rapidly spread to the neighboring countries of Liberia and Sierra Leone.

What's fueling the current outbreak? A few things. The virus has struck densely populated cities, such as Conakry, Guinea, and Monrovia, Liberia. Cases have cropped up in 60 hot spots across a large swath of land.

Since the disease is new to the region, many people aren't aware of how Ebola is transmitted.

And the resources devoted to stopping the outbreak have been limited. Last week, the WHO said more money, people and attention were needed to keep the virus from spreading to more countries.

Vaccine and cure: None. But some small companies have already started looking. They have come up with a few treatments that show promise in animals and are looking to test them in people as early as next year.

Infected patients are quarantined in isolation wards to prevent spreading the virus.

Doctors closely monitor to see if symptoms fade and whether the body has produced antibodies to fight off the infection — usually a hopeful sign for a full recovery.

Patients are declared Ebola-free if they don't show any symptoms for several days and if repeated tests for the virus in their bloodstreams come back negative. (The virus can still linger in semen for months and for a shorter time in breast milk, as the antibodies don't reach those areas. Men who recover are given condoms; mothers are told to wean their children.)

In many cases, the virus weakens the body so much that patients have to stay in the clinic days after they're declared virus-free.

What happens to Ebola survivors? Suffering through Ebola is a traumatic experience in itself. Returning home from an isolation ward can also be a challenge.

Ebola survivors are likely to be shunned and isolated by their communities.

Many people still think survivors are contagious. This is where education and grand gestures from health care workers — a big kiss on the patient's cheek — can help to mitigate the stigma.