The economic impact of Ebola on African economies in 2015 will be less severe than previously thought, the World Bank said in a report on Tuesday, causing just a fraction of the more than $25 billion in losses first expected.

The GDP impact on countries beyond the three directly affected -- Guinea, Liberia and Sierra Leone -- is now estimated at $500 million as governments make progress in fighting the disease.

The first Ebola outbreak in West Africa began 13 months ago when a Guinean toddler became infected with the hemorrhagic fever.

It has spread within the region, killing more than 8,000 people, although countries like Nigeria, Mali and Senegal have succeeded in eradicating it and there are signs other affected countries are making progress.

"I am very encouraged to see Ebola transmission rates slowing markedly in Guinea, Liberia, and Sierra Leone, and that other potential outbreaks have been averted because of swift action by other West African governments," Jim Yong Kim, President of the World Bank Group, said in the report.

Still, the virus will have a major impact on countries directly affected, resulting in at least $1.6 billion in lost economic growth this year or over 12 percent of their combined GDP's.

If Ebola spreads to more countries, the cost for African economies could be as high as $6 billion, the report said.

Sub-Saharan Africa will grow by 4.6 percent in 2015, down slightly from the 5 percent the bank originally forecast due to Ebola as well as falling oil and commodity prices.

(Reporting by Emma Farge; Editing by Matthew Mpoke Bigg and Raissa Kasolowsky)