The World Health Organization says the outbreak of Ebola virus in the Democratic Republic of Congo is now the second-worst in history, after the devastating 2014-2016 West African epidemic.

While the threat is high locally, the WHO says the threat of international spread outside the region remains low. Here are some answers to common questions about Ebola:

What is Ebola virus?

Ebola is a virus that causes a hemorrhagic fever. It’s named after a river in the Democratic Republic of Congo, where it was first discovered in 1976, when the country was known as Zaire. It’s usually seen in remote areas but Ebola caused an epidemic in the west African countries of Sierra Leone, Guinea and Liberia in 2014-2016, infecting at least 28,000 people and killing 11,000 of them.

Where did Ebola come from?

Ebola crops up regularly across the tropical zones of Africa, so it’s clear that it survives in reservoirs of forest animals. Bats are the No. 1 suspect, but it’s unlikely bats cause every outbreak. Bush meat is one possibility — Ebola can infect apes and monkeys, and people in affected areas often hunt these animals for food. Antelope and porcupines also can spread Ebola when slaughtered. One thing is clear — once there is an outbreak, it’s spread from person to person.

Is Ebola deadly?

Ebola virus is very deadly. It kills anywhere from 50 to 90 percent of patients, depending on the strain and where the outbreak is. Doctors say patients die from the effects of high fever, vomiting and diarrhea, but early treatment can often save lives. If patients are treated soon enough, electrolyte solution can help stabilize them while their body fights the infection.

Is Ebola contagious?

Ebola is contagious, but it’s not as easily transmitted as influenza or the measles. It is spread by bodily fluids such as blood, diarrhea, sweat and vomit. Ebola makes patients very sick and causes extreme diarrhea, so people caring for Ebola patients are at risk, as are people preparing the bodies of victims for burial. Fictionalized accounts paint lurid pictures of people bleeding to death from Ebola, and the bleeding is perhaps the most horrific aspect of the infection. But Ebola doesn’t always cause bleeding and it’s hardly ever profuse bleeding on the outside.

How does Ebola spread?

The virus often spreads when people wash the bodies of the dead for burial. It can also be spread sexually and can stay in a man’s sperm, for instance, for months after he recovers. It does not spread in the air. People are most contagious when they are very sick or dying from Ebola, so health care workers are often at the highest risk of infection.

Is there a cure for Ebola?

There’s not a proven specific cure for Ebola. Supportive care can help a lot. People who get treated in modern facilities often recover from the virus. Simply replacing the body fluids lost as people suffer severe diarrhea can help keep them alive, doctors say. There are some experimental drugs for Ebola but they have not been tested in enough people to tell whether they work. ZMapp, a combination of three immune system antibodies, is one experimental treatment, but it must be kept frozen and is not easy to distribute in the remote tropical areas that are usually hit by the virus. Other experimental drugs include favipiravir and GS-5734, but they have not been tested in enough people to show whether they work.

Is there a vaccine against Ebola?

There are several experimental vaccines and one is being made by Merck and is being used in the Democratic Republic of Congo outbreak. Tests in Guinea at the tail end of the 2014-2016 Ebola epidemic in West Africa indicated it did save some people from infection. Health workers are trying to use it in a technique called ring vaccination, in which cases of the disease are tracked down and all the people they have been in direct contact with are vaccinated. Then the contacts of those vaccinated people are tracked down and vaccinated. This method eradicated smallpox at the end of the 1970s.