Reconstruction of outbreak, which has killed more that 11,000 people, found virus might have been contained had Ebola been diagnosed one month earlier
Ian Sample Science editor
Scientists have analysed the genetic code of Ebola viruses from patients across west Africa and pieced together the evolution of the worst ever outbreak of the killer disease.
Experts from the Health Protection Agency at Porton Down in Britain, the World Health Organisation (WHO), and other leading labs, used DNA from 179 Ebola samples to reconstruct the spread of the virus from Guinea into surrounding countries last year.
The study found that the initial outbreak had been dying out in Guinea in early 2014 and might have been contained had the international community diagnosed Ebola just one month earlier than it did. The outbreak has so far recorded 27,000 cases and killed more than 11,000 people.
The analysis shows that the original circulating strain in Guinea died out in July 2014, but not before it was taken to Sierra Leone in May, perhaps by someone who became infected when they visited Guinea for a funeral. In Freetown, Sierra Leone, the virus mutated as it spread, before being re-imported back into Guinea as a new strain that tore across the country.
“The initial containment was nearly successful. If we’d been out there not at the end of March, but in February, maybe this would never have happened,” said Miles Carroll, head of microbiology research at Public Health England. “We could have stopped a lot of health workers and patients from becoming infected.”
Many researchers trace the origins of the Ebola outbreak back to a two-year-old boy called Emile, who died from the infection a few days after Christmas, in 2013. The boy may have contracted the virus from fruit bats that were roosting in trees near Meliandou, a village in southern Guinea.
The latest analysis, reported in Nature, supports that account, but does not prove it. The virus leapt from an infected animal into a human some time between December 2013 and February 2014, the study found.
Doctors at Médecins Sans Frontières in Guéckédou, a town in southern Guinea near the borders of Sierra Leone and Liberia, sent the first samples of what turned out to be Ebola to labs in Hamburg and Lyon in March 2014. The labs confirmed the identity of the virus and alerted the WHO, which dispatched a rapid response unit called the European Mobile Laboratory to the scene. Tens of scientists travelled with diagnostic equipment to Guinea’s capital, Conakry, and onwards in four-by-fours to Guéckédou. The unit they set up ensured patients with Ebola were not sent to the main hospital, where the infection would easily spread to health workers and patients.
For the latest study, the scientists analysed about 15 Ebola samples taken each month of the outbreak from March 2014 to January 2015. Because the virus mutates over time, the DNA can reveal how the infection spread from one place to another.
According to the study in Nature, the initial outbreak grew around Guéckédou, Macenta and Kissidougou in Guinea in March 2014. By the end of May a new strain of the virus had been carried to Sierra Leone, and also into Liberia. The virus spread rapidly in those countries, before being carried back into Guinea from June 2014 onwards. This second wave was far worse than the first outbreak. In the autumn, the virus crossed twice from Guinea into Mali, from Beyla district in October and from the Siguiri district one month later.
Beyond the light it casts on the way Ebola spread, Carroll said the study shows how, with present technology, we cannot predict where the next outbreak will occur. “What we need is an early warning system that uses real time genetic sequencing, and an effective and rapid response plan,” he said.