Following are the main developments since the worst-ever epidemic of the hermorrhagic fever Ebola emerged in west Africa earlier this year.

The global death toll for the virus has reached 1,229, the World Health Organization said Tuesday, including 466 in Liberia, 394 in Guinea, 365 in Sierra Leone and four in Nigeria.

MARCH 2014

- 22: Guinea identifies the Ebola virus as the source of a highly contagious epidemic raging through its southern forests, as the death toll rises to 59. Scientists studying samples in the French city of Lyon confirm it is Ebola. On the 27th it spreads to Guinea's capital Conakry.

- 31: Liberia confirms two cases of the virus.

APRIL

- 5: West African countries mobilise. Medical teams are deployed at Conakry airport.

- 8: The WHO says the outbreak is among the "most challenging" for health workers since the deadly disease first emerged four decades ago in Zaire, now the Democratic Republic of Congo.

MAY

- 26: Sierra Leone confirms its first fatality.

JUNE

- 21: The WHO says the rapid spread of Ebola in the countries concerned has occurred in part because containment efforts have been too relaxed.

JULY

- 3: The WHO says it expects the Ebola outbreak to continue for at least "several months".

- 25: The virus spreads to Africa's most populous country Nigeria, as a Liberian national dies in quarantine in Lagos. The country places its ports and airports on alert.

- 30: Doctors Without Borders warns that Ebola is out of control and there is a risk of it spreading to other countries.

Liberia announces it is shutting all schools.

AUGUST

- 1: Guinea, Liberia and Sierra Leone announce a cross-border isolation zone around the epicentre of the outbreak.

- 5: The World Bank earmarks up to $200 million (150 million euros) to help contain Ebola.

- 8: The WHO declares the Ebola epidemic a "public health emergency of international concern".

Nigeria follows Liberia and Sierra Leone in declaring a national emergency.

- 12: The WHO authorises the use of experimental drugs in the fight against Ebola, after an ethical debate.

- 13: Liberia receives doses of an experimental Ebola vaccine ZMapp, which has shown positive early results.

Guinea declares a "health emergency", announcing a series of nine measures including strict controls at border points, travel restrictions and a ban on moving bodies.

- 15: The WHO says the magnitude of the Ebola epidemic in West Africa has been "vastly" underestimated. Medical charity MSF says the outbreak is moving faster than medics can handle.

The UN's World Food Programme says will fly in food aid for up to one million people affected by Ebola.

- 18: Cameroon, which has so far been spared Ebola cases, closes all its land, sea and air borders with Nigeria.

- 19: Liberia says it has found 17 Ebola patients who had fled an attack on their clinic and says eight medical workers including two doctors who have been given experimental US-made drug ZMapp are responding to the treatment.