A Doctors Without Borders health worker stands in an Ebola virus treatment center in Conakry, Guinea, November 17, 2015. To match HEALTH-EBOLA/GUINEA REUTERS/Saliou Samb

CONAKRY (Reuters) - Guinea’s Ebola coordination unit has traced an estimated 816 people who may have come into contact with victims of the disease or their corpses during a recent flare-up in a village in the country’s southeast, a health official said on Monday.

Guinea said on Thursday that it had discovered new cases of Ebola just hours after the World Health Organization (WHO) declared neighbouring Sierra Leone’s latest outbreak over. Four people have died in the flare-up in Porokpara.

“Since the start of the tracing on Saturday, we have traced 816 contacts in 107 families,” Fode Tass Sylla, spokesman for the coordination unit, said on state television. “We are optimistic because everyone is motivated and cooperating.”

The villagers will be quarantined in their homes for 21 days, after which time, if they have not developed symptoms, they will be released, Sylla said.

The world’s worst Ebola outbreak on record is believed to have started in Guinea and killed about 2,500 people there by December last year when the WHO announced an end to active transmission in the country.

More than 28,600 people have been infected and 11,300 have died, nearly all of them in Guinea, Liberia and Sierra Leone, since the epidemic began in December 2013.