The virus that has caused a deadly Ebola epidemic in West Africa is a new strain that emerged locally, possibly transmitted by fruit bats, virologists have said.
The spread of Ebola from a remote corner of Guinea to the capital and into neighbouring Liberia, the first deadly outbreak reported in West Africa, has caused panic across a region struggling with weak healthcare systems and porous borders. The World Health Organisation (WHO) warned this week that Ebola could continue to spread in West Africa for months.
Scientists have unravelled the genome of the virus and found it to be distinct from strains in countries where Ebola was already known to circulate. Ebola is endemic to the Democratic Republic of Congo, Uganda, South Sudan and Gabon, and scientists initially believed that Central Africa’s Democratic Republic of Congo strain of the virus was responsible for the outbreak.
Using analysis of blood from infected patients, researchers determined that while the Guinean form of the Ebola virus showed a 97 percent similarity to the Democratic Republic of Congo strain, the disease was not introduced from Central Africa.
The virus is of the EBOV type, one of three species that have caused outbreaks in sub-Saharan Africa, said the preliminary study published on the website of the New England Journal of Medicine on Wednesday.
“This study demonstrates the emergence of EBOV in Guinea,” the authors wrote.
Data from the analysis “suggest a single introduction of the virus into the human population,” probably in early December 2013 “or even before,” according to the study.
“It is suspected that the virus was transmitted for months before the outbreak became apparent,” it added.
“This length of exposure appears to have allowed many transmission chains and thus increased the number of cases of Ebola virus disease.”
‘Potential reservoirs’ of the virus
The study said fruit bats found throughout West Africa were “potential reservoirs” of the virus.
“It is possible that EBOV has circulated undetected in this region for some time,” said the authors.
Of the 197 clinical cases of Ebola in Guinea, 122 have died including several health workers, according to a World Health Organisation update released on Thursday, which cited Guinean health ministry figures. Sixteen of those died in the capital Conakry. Liberia’s health ministry has recorded at least 13 deaths from 26 confirmed and suspected cases of Ebola.
The fatality rate was between 71 and 86 percent in the cases they studied, the researchers wrote.
Guinea’s health ministry said on Tuesday that the number of new cases had fallen rapidly and the outbreak was nearly under control.
On Tuesday, Dr. Keiji Fukuda of the WHO warned that it’s too early to say whether the rate of transmission is slowing. He said that while other outbreaks have seen more cases, the current one is remarkable for the wide area over which it has spread.
“We fully expect to be engaged in this outbreak for another two, three, four months,” Fukuda, who is the assistant director-general of the health security and environment cluster at the UN health agency, told reporters in a conference call from Geneva.
On Thursday, a senior health ministry official in Guinea told Reuters that the government planned to stop releasing the death toll to avoid causing panic.
Last week an angry crowd attacked a treatment centre in Guinea last week, accusing Doctors Without Borders of bringing the virus to the country.
There is no known vaccine or cure for Ebola, a haemorrhagic fever that causes symptoms ranging from flu-like pains to internal and external bleeding caused by kidney and liver failure.
People can contract the disease from handling the blood or other bodily fluids of sick or dead forest animals.