Seven people have died in north-western Congo after 11 died earlier this month, say health officials.
The latest outbreak of Ebola is believed to have started when a family ate a wild boar they had found dead.
Health workers have blamed the rapid spread of the disease on traditional practices, such as washing and kissing the body of the dead.
The same region was quarantined last year, after an outbreak of the highly contagious disease killed 100 people.
The new deaths were recorded in Mbomo and Mbanza in Cuvette Ouest province.
Thirty-three more cases have been reported in the area but heavy rains are hampering efforts to fight the outbreak.
Burial training
Aid agency Medecins Sans Frontieres says it took their team four days to travel the 728km from Brazzaville to the affected area.
MSF is training burial teams using culturally sensitive yet safe techniques for preparing and burying the dead.
"It is most distressing that five trained health workers have now died of Ebola in Cuvette Ouest since 2002, and yet we see very little effort to improve access to healthcare, train new staff or care for the victims of this and other sickness in the Republic of Congo," said MSF head of mission Paul Foreman.
Ebola passes quickly from person to person, through bodily fluids such as mucus, saliva and blood.
It causes massive internal haemorrhaging and leads to death in as many as 90% of those who become infected.
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