Liberia declared free of Ebola, WHO warns of possible 'flare-ups'

Liberia has been declared Ebola-free by the World Health Organization (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.

WHO chief Margaret Chan said the end of the outbreak was a "monumental achievement".

"This date marks the first time since the start of the epidemic two years ago that all three of the hardest-hit countries - Guinea, Liberia and Sierra Leone - have reported zero cases for at least 42 days," she said in a statement.

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

WHO said it anticipated "more flare-ups", and the risk of additional small outbreaks in the three West African states remained "high".

"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.