LONDON (AP) — The World Health Organization has declared that Nigeria is now free of Ebola.

A teacher checks body temperature of pupils for the Ebola virus at a school in Lagos on October 8, 2014. The World Health Organization declared Nigeria to be free of Ebola on October 20, a rare instance of authorities turning the tide on the highly contagious disease that has killed more than 4,000 in West Africa. (Pius Utomi Ekpei/AFP/Getty Images)

In an update issued Monday, the U.N. health agency said the country's containment of the lethal disease was a "spectacular success story."

The West African nations at the center of the Ebola outbreak, including Guinea and Liberia, are in red, while Senegal, left, and Nigeria, right, both in green, have recently been declared free of the disease by the WHO. (Image via TheBlaze/Wikimedia Commons)

The announcement comes after 42 days have passed — twice the disease's maximum incubation period — since the last case in Nigeria tested negative.

WHO said Nigeria had traced nearly every contact of Ebola patients in the country, all of whom were linked to the country's first patient, a Liberian man who arrived with symptoms in Lagos and later died. Nigeria reported 20 cases of Ebola, including eight deaths.

For an outbreak to be declared officially over, WHO convenes a committee on surveillance, epidemiology and lab testing to determine that all conditions have been met.

This story has been updated.

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