A fourth person has likely died from Ebola in remote northeastern Democratic Republic of Congo, the World Health Organization said on Sunday, as the overall number of cases rose to 37 from 29.

Of the 37 cases of hemorrhagic fever discovered since early May, two have been confirmed as Ebola, three, including the latest death, are considered probable and 32 are suspected, WHO's Congo spokesman Eugene Kabambi told Reuters.

Health authorities are monitoring 416 people who came into contact with sufferers and have dispatched mobile laboratories to the zone to more quickly test people who display symptoms, Kabambi said.

The affected zone's extreme isolation has helped contain the highly contagious virus' spread, though a lack of telecommunications, few paved roads and a shortage of thermometers have hindered the response.