The latest outbreak of the Ebola virus in Africa is the deadliest in recorded history. It has killed at least 729 people since March and infected more than 1,000, including several Americans.
The grave situation prompted the Centers for Disease Control and Prevention to issue travel warnings on Thursday to Guinea, Liberia and Sierra Leone. They urged travelers to forgo all nonessential travel to those countries.
The World Health Organization (WHO) calls Ebola one of the world's most deadly diseases, but what exactly is it? And why is it spreading? Here's 10 things to know:
1. What is Ebola?
The Ebola virus disease is a severe, contagious illness that damages the vascular system, causing bleeding and high fevers. It has a high fatality rate: from 60 to 90 percent.
The virus first appeared in 1976 in two simultaneous outbreaks, one in Sudan and one in the Democratic Republic of Congo. The latter occurred close to the Ebola River, which gave the disease its name.
Ebola is almost entirely confined to Africa. It usually appears in waves of outbreaks, partly because when someone contracts the virus, it spreads from person to person so fast that it's difficult to contain.
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2. Why have we heard so much about this particular outbreak?
In March, Guinea received confirmation that Ebola was the illness responsible for an alarming number of deaths. The disease has since reached Sierra Leone, Liberia and Nigeria, making this the deadliest Ebola outbreak ever.
This outbreak is also worrying because of its geography. The regions affected today are in West Africa, but this strain of the virus is native to the forests of Central Africa. It is not yet known how the disease was carried from one region to the other.
Doctors Without Borders said the disease, which has been raging for months, is "totally out of control," and efforts to stop its spread have proved difficult.
3. Why is the disease reported only in Africa?
There are five strains of Ebola: Four are native to Africa, but one is actually native to the Philippines and China. The only place that the disease has been observed spreading from animals to humans is Africa.
The disease is generally spread to humans from animals native to specific regions of Africa, including primates, rats and bats. Contagion may occur from handling infected animals, ingesting infected meat from these animals, or contact with their bodily secretions.
Ebola spreads especially quickly in some African countries due to misinformation. Some hunters eat infected "bushmeat." Some burial procedures encourage close contact between mourners and infected corpses.
Health professionals have had difficulty convincing people to follow strict isolation procedures that might help contain the spread of the virus.
4. Why is it so deadly?
The Ebola virus causes severe bleeding and organ failure. Initial symptoms include fever, weakness, muscle pain, headache and sore throat. These symptoms are followed by vomiting, diarrhea, rashes, impaired kidney and liver function, and sometimes internal and external bleeding, according to WHO.
In short, the virus finds a way to rob the body of both blood and fluids, a particularly deadly combination. Other research showed that the virus may also suppress immune response. Death rates are also elevated by poor health care in the countries where Ebola has struck.
5. Why does it spread so fast?
Dr. Gary L. Simon of the George Washington University specializes in infectious diseases and tropical medicine. He said that the disease is not actually all that contagious -- but quarantine practices in certain African countries have been difficult to enforce.
When a person comes into contact with an infected person or animal, transmission occurs from direct contact (through broken skin or mucous membranes) with blood or other bodily fluids like stool, urine, saliva, sweat and semen.
The disease is also difficult to detect in the early stages, as it shares symptoms with many other diseases. By the time the virus is detected, the infected person will be very sick and will likely have transmitted Ebola to other people.
6. Is there a cure?
There is no known cure. An experimental serum was provided Thursday to a U.S. charity worker in Liberia who is infected with the disease.
"Supportive therapy" to regulate a person's bodily temperature and blood pressure is the only treatment.
Dr. Jackie Eghari-Sabet, of the Family Allergy and Asthma Care in Maryland, compared the search for an Ebola cure to that of the search for an HIV cure. She said virologists have a lot of experience to work from.
7. When are people contagious?
People are infectious as long as their blood and secretions contain the virus. The incubation period (the time interval from infection with the virus to onset of symptoms) is two to 21 days. In one case, Ebola virus was isolated from semen in a man who was infected in a laboratory 61 days prior.
8. Are there any lasting effects in survivors?
Although fatality rates are high, some people do survive Ebola. Medical experts are still trying to understand why Ebola has such a low survival rate; they say any chance of beating it depends on early access to medical care when the first symptoms show up.
Most people who survive Ebola will likely be able to return to a normal life; however, they may develop certain chronic conditions affecting their joints and eyes. These problems could stick around for the rest of a survivor’s life.
9. Has Ebola ever left Africa?
Yes, but only in primates. Three of these events occurred in America: in 1989, 1990 and 1996.
In 1989 and 1990, quarantine facilities in Reston, Virginia, as well as Pennsylvania and Texas, saw a new strain of the disease in infected monkeys imported from the Philippines. The virus was known as the "Reston virus." The same happened in Texas in 1996. No human got sick in any of those cases.
Emory University Hospital in Atlanta will receive one of the infected American health workers for treatment in an isolation unit, the hospital announced Thursday.
10. Are authorities testing travelers at U.S. airports?
Not currently. GW's Dr. Simon said that, in his opinion, to do so would be "foolish."
"This is not a hugely infectious disease, if only about 1,000 people in a population of millions have contracted it," he said.
The volume of travelers through the airports would make such testing very difficult, slow and expensive. Also, the risk of transmitting the disease from one passenger to another during a flight is low.
At the moment, the risk is contained to certain patches of the Southwest and Central Africa, and the CDC doesn't consider the risk of Ebola infection in the U.S. significant.
Dr. Simon said he thought that if the virus reached the U.S., it would not be as much of an issue as it currently is in Africa.
"I think we could contain it," he said. "We have very good isolation procedures here."