The World Health Organization deployed specialists to southeast Guinea on Friday after two new Ebola cases were confirmed.
The cases were announced just hours after Sierra Leone heralded the end of its recent Ebola flare-up, again dashing hopes that the deadly disease was gone from West Africa.
The new cases occurred in Koropara, in the remote N'Zerekore prefecture in southeast Guinea, 1,000 kilometers (620 miles) from the capital, said Ibrahima Sylla, a spokesman for the national coordination for the fight against Ebola.
Guinea officials on Wednesday alerted WHO to three unexplained deaths in Koropara and said members of the same family were showing Ebola symptoms, according to a statement from WHO issued Friday. Samples were taken from four people.
"A mother and her 5-year-old son, relatives of the deceased, confirmed positive for Ebola virus disease in lab tests," WHO said. The two have been taken to a treatment facility, WHO said.
WHO sent specialists including surveillance experts and contact tracers to N'Zerekore, and more specialists should arrive "in the coming days," according to the statement.
The deadliest Ebola outbreak in history has killed more than 11,300 people, mostly in Sierra Leone, Liberia and Guinea.
Guinea, where the first cases were confirmed in early 2014, was declared free of Ebola transmission on Dec. 29. It was on track to celebrate the end of its 90-day heightened surveillance period at the end of March.
Experts have long warned that more flare-ups are likely and have urged health officials to remain ready to respond to new cases.