Rich countries must act swiftly to repair battered health systems and get cash to millions of families in the three countries hit hardest by the world's worst Ebola outbreak, the international development agency Oxfam said Tuesday.

Though the economies of Sierra Leone, Guinea and Liberia were recording strong growth prior to the outbreak, the countries remain some of the world's poorest and incomes have shrunk dramatically since the first Ebola cases were confirmed in Guinea last March.

New cases now appear to be on the wane, but Oxfam said donor countries should commit to a post-Ebola "Marshall Plan" that would address urgent cash shortages and crippling damage to social services like health, education and water and sanitation.

Families in the three countries have "gone through hell," Oxfam GB Chief Executive Mark Goldring said, in no small part because the international community reacted slowly during the early stages of the outbreak.

"The world cannot walk away now that, thankfully, cases of this deadly disease are dropping. Failure to help these countries after surviving Ebola will condemn them to a double-disaster," Goldring said.

Oxfam research from three counties in Liberia, the country with the most Ebola deaths, shows that 73 per cent of families are facing income declines averaging 39 per cent.

The lack of money combined with high food prices mean 60 per cent of people have not had enough to eat in the last seven days, Oxfam said.

Ebola has killed more than 8,600 people in Liberia, Sierra Leone and Guinea, according to the World Health Organization -- a total that includes confirmed, suspected and probable deaths.

On Sunday, several dozen of WHO's member countries approved a resolution aimed at strengthening the U.N. health agency's ability to respond to emergencies after a sluggish performance that experts say cost thousands of lives.

Even as aid agencies look to the recovery effort, Doctors Without Borders warned this week that "critical gaps" in countries' efforts to trace Ebola contacts could lead to new surges in cases.