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More than 1.4million people are expected to be infected by the Ebola virus by January as it spreads exponentially across Africa.
Over 3,000 people have been killed by the virus so far, and at a major conference in London yesterday there were calls for international military forces to get involved to help stop its spread.
Here's what you need to know:
Ebola first identified in village in northern Zaire in 1976. It is named after nearby Ebola River. Several sporadic outbreaks occur in east and west Africa in next four decades.
Guinea confirms that unidentified fever that killed more than 50 is Ebola. Liberia reports two cases.
WHO confirms first Ebola deaths in Sierra Leone.
International death toll exceeds 350, making it worst Ebola outbreak in history.
Nigeria confirms first case. Liberia deploys troops to enforce quarantine areas.
WHO declares international public health emergency. Death toll reaches 1,550. Senegal reports first case.
US promises to send 3,000 military personnel to region. Ebola largely contained in Nigeria and Senegal but death toll in three worst-hit countries rises to more than 3,000.
Official death toll is 3,330 but experts believe true figure is higher due to underreporting. They say that 1.4 million could be infected by January if more is not done.
Sources: World Health Organisation, Centers for Disease Control and Prevention
More: Why it's not time to panic about Ebola in Britain