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Liberia’s Ebola epidemic is over, says the World Health Organisation (WHO), effectively putting an end to the world's worst outbreak of the disease.

The "end of active transmission" was declared, after 42 days without a new case in Liberia.

It joins Guinea and Sierra Leone, which earned the status last year.

However, the WHO warned that West Africa may see flare-ups of the virus. It has killed more than 11,000 people since December 2013.

A country is considered free of human-to-human transmission once two 21-day incubation periods have passed since the last known case tested negative for a second time.

The WHO said in a statement that "all known chains of transmission have been stopped in West Africa", with no cases reported for at least 42 days in Liberia, Guinea and Sierra Leone, the three states hardest-hit by the outbreak.

"So much was needed and so much was accomplished by national authorities, heroic health workers, civil society, local and international organisations and generous partners," said WHO chief Margaret Chan.

However, the end of active transmission of Ebola has been declared twice before in Liberia - only for the infection to re-emerge.

This is why the declaration will be marked with caution, says BBC Africa.

The WHO said it anticipated "more flare-ups", and Liberia, Sierra Leone and Guinea "remain at high risk of additional small outbreaks" of Ebola.

"Evidence shows that the virus disappears relatively quickly from survivors, but can remain in the semen of a small number of male survivors for as long as one year, and in rare instances, be transmitted to intimate partners," it added.

"By the end of this year, we expect that all survivors will have cleared the virus from their bodies," Dr Chan was quoted as saying by the AFP news agency.

Medical charity Medecins Sans Frontieres (MSF) said in a statement that the end of the "devastating and unprecedented epidemic" was a day of celebration and relief.