BENI, Congo (AP) — A 5-year-old boy vomiting blood has become the first cross-border case of Ebola in the current deadly outbreak. Now authorities in Congo are trying to determine how his family, exposed to the virus, managed to cross into neighboring Uganda.

The World Health Organization late Tuesday confirmed the first Ebola case outside Congo since the outbreak began in August. Nearly 1,400 people have died.

Congo's health ministry says a dozen members of the boy's family had showed symptoms of Ebola and were put in isolation.

But six managed to leave while awaiting transfer to an Ebola treatment center. Authorities say they entered Uganda, where the boy is receiving treatment and relatives are isolated.

Experts have long feared Ebola could spread to neighboring countries because of unrest hampering response work in Congo.