There is no cure for Ebola haemorrhagic fever.

More than half of people infected in this outbreak have died. Death rates in some past outbreaks reached 90 per cent.

It's a cruel end that comes within days. Patients grow feverish and weak, suffering through body aches, vomiting, diarrhoea and internal bleeding, sometimes bleeding from the nose and ears.

Because it's spread through direct contact with the body fluids of sick patients, Ebola takes an especially harsh toll on doctors and nurses, already in short supply in areas of Africa hit by the disease.

Watch: What do Hongkongers think about Ebola?

Health workers and clinics have come under attack from residents, who sometimes blame foreign doctors for the deaths. People with Ebola or other illnesses may fear going to a hospital or may be shunned by friends and neighbours.

Two of the worst-hit countries - Liberia and Sierra Leone - sent troops to quarantine areas with Ebola cases. The aim was to stop the disease's spread, but the action also created hardship for many residents.

The outbreak began in Guinea in March before spreading to neighbouring Sierra Leone and Liberia. A traveller recently carried it farther, to Nigeria, leading to a few cases in the giant city of Lagos, which has a population of more than 20 million.

Ebola emerged in 1976. It has been confirmed in 10 African nations, but never before in the region of West Africa.

Lack of experience with the disease there has contributed to its spread. So has a shortage of medical personnel and supplies, widespread poverty and political instability.

Sierra Leone is recovering from a decade of civil war in which children were forced into fighting. Liberia also endured civil war in the 1990s.

Guinea is trying to establish a young and fragile democracy. Nigeria, Africa's most populous country, boasts great oil wealth, but most of its people are poor. The government is battling Islamic militants in the north who have killed thousands of people and kidnapped more than 200 schoolgirls in April.

This outbreak has proved more difficult to control than previous ones because the disease is crossing national borders and is spreading in more urban areas.

Tom Frieden (inset), director of the US Centres for Disease Control (CDC) and Prevention, predicts that within a few weeks, Ebola will sicken more people than all previous occurrences combined. Already almost 1,800 cases have been reported.

Global health officials say it will take months to fully contain the outbreak.

But most people don't need to fear Ebola. The virus doesn't spread easily, the way a cold does. Ebola spreads only by direct contact with bodily fluids such as blood, saliva, sweat and urine. Family members have contracted it by caring for their relatives or handling an infected body at burial. People aren't contagious until they show symptoms, Frieden said. Symptoms may not appear until 21 days after exposure.

"People should not be afraid of casual exposure on a subway or an airplane," said Dr Robert Black, a professor of international health at Johns Hopkins University in the US.

Health officials around the developed world know how to stop Ebola. Frieden described tried-and-true measures: find and isolate all possible patients, track down people they may have exposed and ensure strict infection-control procedures while caring for patients. Every past outbreak of Ebola has been brought under control.

China will send disease control experts to West Africa and the US CDC is sending at least 50 staff members to to help fight the disease. More than 200 experts will also work on the problem from CDC's headquarters in Atlanta.

Ebola's toll is minuscule compared with other diseases that kill millions of people.

"The difference is the diseases that do kill a lot of people - malaria, diarrhoea, pneumonia - they cause their problems over time," Black said.