Ebola: How did it get there?

Understanding Ebola

Fighting the fever

Aug 8th 2014, 16:22 by C.B. | BAMAKO

WITH around 1,700 suspected cases and more than 900 deaths, the outbreak of Ebola haemorrhagic fever in four West African countries is the biggest ever recorded. On August 8th the World Health Organisation (WHO) declared the epidemic an "international emergency".

One reason for Ebola's frightening reputation (after all, quotidian diseases such as  tuberculosis and malaria kill far more people than it does) is that comparatively little is known about it. Funding to study rare diseases that afflict the very poor is notoriously hard to come by (what little there is tends to come from armies). But a few scientists are nonetheless trying to piece together the story. Understanding the preconditions for an Ebola outbreak, after all, is the first step in preventing future epidemics from happening.

The most striking thing about the present outbreak, says Andrew Townsend Peterson, an evolutionary biologist at the University of Kansas who is interested in modelling the spread of Ebola, is that it seems to involve the Zaire strain of the disease, the deadliest of the five subtypes of Ebola known to medicine. But Zaire—the name for the country now known as the Democratic Republic of the Congo—is a long way from Guinea, where the first cases seem to have arisen in December 2013. How did the virus cross that distance?

One possibility, according to a paper published on July 31st in PLOS Neglected Tropical Diseases, by Dr Daniel Bausch and Lara Scwarz, of McGill University, is that it didn't. The present strain may be a sixth version of the virus, hitherto unknown to medicine. But although the limited genetic data gathered thus far do not refute that idea completely, they do cast doubt. The virus's genome is not exactly the same as the sort found in Central Africa. But it is 97% similar. 

If it is indeed the Zaire strain, though, then someone, or something, must have brought the bug to Guinea. Human transmission seems unlikely, write the researchers. The centre of the outbreak is isolated and little-visited by outsiders. Besides, this particular strain of the disease seems to kill its victims within a week of symptoms appearing. That does not seem like enough time to get from Central Africa to the backwoods of Guinea.

The other possibility is that the virus was brought by an animal, probably a bat. Scientists have long suspected that certain species of fruit bat harbour the disease naturally. These bats are common throughout sub-Saharan Africa, and are thought by zoologists to be capable of migrating great distances. An outbreak of Ebola in Gabon in 2002 is thought to have started when an infected bat was eaten.

The researchers also point out that, contrary to what is often believed, Ebola outbreaks do not seem to happen at random. Human factors play a big part. Ebola, like many other diseases, mainly menaces those countries that are already poor and struggling. Guinea is ranked by the UN as one of the poorest countries in the world. In recent years Ebola has also struck in DRC, Sudan, Uganda, Sierra Leone and Liberia, all countries where civil wars have left deep scars. Urgent need drives people to cut down forests, hunt bushmeat and plunder caves, bringing them into contact with the wild animals thought to harbour the disease, and providing the virus with opportunities to jump to humans.

Run-down health facilities are the second link in the chain. Contrary to popular belief, Ebola is not particularly easy to catch, spreading only via close contact with the bodily fluids of the very sick. "If you come to a hospital in New York with vomiting or bleeding, healthcare workers use gloves," says Dr Bausch. "[But] if you go to a hospital in Guinea, they might say 'we just don't have any gloves'". Doctors and nurses contract the virus, spread it to other patients and then bring it home to their families. In this epidemic, more than 160 health care workers have been infected, and around 80 have died.

Unprepared or ineffective governments make things worse again. Lack of communication speeds the disease's spread. Fear, rumour, and suspicion of government workers and foreign doctors can make the infected reluctant to come forward, increasing the chance that they will pass on the sickness, often to members of their families who are caring for them.

Billy Fischer, an American doctor from the University of North Carolina, who went to Guinea in June, described Ebola's horrible intimacy in letters home: "Part of what makes Ebola so devastating in addition to the manner in which people die, is that this virus wipes out families. It penalises those families who are close and transforms tradition into transmission."

Originally this post suggested 100 health care workers had been infected. By Friday that number was 160, about half of whom have died.

Source: http://www.economist.com/blogs/babbage/2014/08/understanding-ebola