Ebola
Health workers take blood samples for Ebola virus testing at a screening tent in the local government hospital in Kenema, Sierra Leone, June 30, 2014. Photo by Reuters
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Ebola has captivated the world's attention because it's a terrifying disease – and the deadly haemorrhagic fever is caused by a virus, meaning there's no cure. Yet although West Africa is suffering its worst-known outbreak and just today the Emirates airline suspended flights to Guinea indefinitely because of the disease – the danger of a global pandemic remains small, say scientists.

One problem with containing its spread is that Ebola symptoms may appear as late as three weeks after infection. Meanwhile the victim may have traveled anywhere in the world, taking the virus with him. At least one case in today's outbreak is known – Lagos, Nigeria went into crisis mode after a sick Liberian-American, Patrick Sawyer, landed there from Liberia on July 20 and promptly collapsed. He was taken to hospital and died five days later.

On Saturday, Dr. Kent Brantly, an American healthcare specialist working in Liberia, was taken to the Emory University Hospital in Atlanta for treatment. Throughout his trip, special precautions to prevent infection were taken.

Yes, there is a risk of the disease spreading as unwitting carriers travel. But, as Scientific American reports, the number of people known to be infected right now remains small, and Ebola is not highly contagious and by the time symptoms develop to the point of infectivity, the carrier is probably too sick to travel anyway.

What happens as the virus gains hold is that it breaks down the body's internal organs by increasing the permeability of blood vessels. Not only do the vessels start to leak blood: coagulation is impaired. The virus can also infect white blood cells. While the initial symptoms are rather like flu, the tell-tale sign that it's something else come  later in the form of hemorrhagic signs, including bleeding from the gums, eyes and nose. Also, as the disease progresses, patients also suffer diarrhea, vomiting, low blood pressure, pain and exhaustion.

Death, if it does result, comes from multiple organ failure and shock, and all modern medicine can do about any of this is treat the symptoms and hope the patient's immune system overcomes.

Everybody in the taxi died

Meanwhile the West Africa outbreak, which began in Guinea in February, has reached the neighboring countries of Liberia and Sierra Leone. More than 1,300 cases have been reported so far, of whom 729 have died.

The disease is believed to have spread from Guinea to Liberia in March, carried by a woman who since died – as did her sister who cared for her. Before dying, the sister traveled by shared taxi to visit her husband on the other side of Liberia. The other passengers caught the disease and died.

Yet unlike the flu, for instance, Ebola can only spread through physical contact, not the air. To catch it, a person's mucous membranes (or any cut in the skin) must come into direct contact with infected fluids - blood, urine, saliva, semen or feces, reports Scientific American. Direct contact with clothing or bed linen contaminated with these fluids can also lead to infection.

You can't catch it from a door-knob, they elaborate. And crucially, a pre-symptomatic carrier isn't infectious.

The sheer deadliness of Ebola – the present disease's mortality rate has been calculated at 56%- is another reason it's unlikely to become a global threat, say infectious disease specialists.

Too sick to travel

Patients are at the most infectious when the haemorrhagic fever is in its terminal stages, inducing both internal and external bleeding, and profuse vomiting and diarrhea - all of which contain high concentrations of infectious virus.

Anyone at this stage of the illness is close to death – and is probably also too ill to travel, explains Bruce Hirsch, an infectious diseases expert at North Shore University Hospital in the United States.

"It is possible, of course, for a person to think he might just be coming down with the flu, and to get onto transport and then develop more critical illness. That's one of the things we are concerned about," he said in a telephone interview. He added, however: "The risk (of Ebola spreading to Europe or the United States) is not zero, but it is very small."

Heymann noted that the only case in which an Ebola case was known to have left Africa and made it to Europe via air travel was in 1994 when a Swiss zoologist became infected with the virus after dissecting a chimpanzee in Ivory Coast. The woman was isolated in a Swiss hospital and discharged after two weeks without infecting anyone else.

"Outbreaks can be stopped with good infection control and with understanding by people who have been in contact with infected cases that they have to be responsible," Heymann said.