Health workers have called the Ebola outbreak in West Africa unprecedented, overwhelming and even out of control.
With 1,711 cases so far, it's the largest and deadliest outbreak since the virus was discovered in 1976. And it's gathering strength: Just under 20 percent of all cases were reported over the last week, from July 28 through August 4. Nearly all cases are still in the three countries at the epicenter of the crisis: Guinea, Sierra Leone and Liberia. But the virus has also spread to Nigeria, where the government is reporting two deaths and more than a half-dozen cases.
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 932 deaths. That puts the current mortality rate at about 55 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, stool and vomit.
In one outbreak, researchers found evidence that people caught the virus from infected fruit bats, which were sold at a market for food. Nonhuman primates, such as monkeys, chimpanzees and gorillas, also likely spread Ebola when people hunt and eat these animals.
People infected with Ebola are contagious only after they start showing symptoms. For that reason, health care workers and family members caring for the sick are at the greatest risk for catching the virus.
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; Monrovia, Liberia; and Lagos, Nigeria. Cases have cropped up in more than 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.
Treatment: 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.
There are no drugs or vaccines approved for Ebola. But several companies and labs are working on experimental treatments, such as serums that contain antibodies to the virus. In July, two American aid workers were given an experimental medicine, called ZMapp. So far, they are the only people to have been treated with the medication. And it's too soon to know if the drug works.
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.