A factfile on the Ebola virus that has plunged Guinea into an "epidemic situation" according to a senior health official, and which has killed more than 15,000 people since 1976.
Ebola was first identified in central Africa in 1976. The tropical virus was named after a river in the Democratic Republic of Congo -- then known as Zaire.
Five of the virus species are known to cause disease in humans -- Zaire, Sudan, Bundibugyo, Reston and Tai Forest.
The first three species have resulted in serious African outbreaks.
The virus' natural reservoir animal is probably the bat, which does not itself fall ill, but can pass the germ on to humans who hunt it for "bushmeat".
Other dinnertime favorites in parts of Africa -- chimpanzees, gorillas, monkeys, forest antelope and porcupines -- are also suspected of transmitting Ebola.
Among humans, the virus is passed on by contact with the blood, body fluids, secretions or organs of an infected or recently deceased person. This can include touching a sick or dead person, and likely also sexual intercourse.
Those infected do not become contagious until symptoms appear. They become more and more contagious until just after their death, which poses great risks during funerals.
Death rates are high, at around 50% on average of those infected, and up to 90% for some epidemics, World Health Organization (WHO) data shows.
Following an incubation period of between two and 21 days, Ebola develops into a high fever, weakness, intense muscle and joint pain, headaches and a sore throat.
The initial symptoms are often followed by vomiting and diarrhea, skin eruptions, kidney and liver failure, and internal and external bleeding.
After effects have often been observed in survivors, including arthritis, problems with vision, eye inflammation and hearing difficulties.
A vaccine developed by the U.S. group Merck Shape and Dohme was found to be very effective in a major study carried out in Guinea in 2015.
It was pre-qualified by the WHO and more than 300,000 doses have been used during a vaccination program in the Democratic Republic of Congo (DR Congo).
A second experimental vaccine developed by the U.S. group Johnson & Johnson was introduced preventively in October 2019 in areas that had not been affected by the virus, and more than 20,000 people were inoculated.
Worst epidemic (2013-2016)
The worst-ever Ebola outbreak began in December 2013 in southern Guinea before spreading to two neighboring west African countries, Liberia and Sierra Leone.
That outbreak killed more than 11,300 people out of nearly 29,000 registered cases, according to WHO estimates.
10th and 11th DR Congo epidemics
The 10th epidemic began on August 1, 2018 in the North Kivu province of DR Congo, and was declared a global health threat in July 2019 by the WHO.
It was declared over in June 2020 by DR Congo authorities after around 2,280 people had died, making it Africa's second worst Ebola outbreak ever.
An 11th Ebola epidemic began that month in the Equator province and was declared over on November 18, with 55 deaths.
'Resurgence' in DR Congo and "epidemic situation in Guinea
On Feb. 7, the DR Congo said a resurgence of the virus had been identified in an eastern part of the country.
A week later, a senior health official in Guinea said that country was in an "epidemic situation" after seven cases were confirmed in the southeast, three of which had resulted in deaths.
They were the first Ebola fatalities in Guinea since 2016.
A local WHO official said the organisation would send vaccines quickly to help keep the virus from spreading.