I've read one report suggesting fruit bats might be a vector. The bats,it was guessed,might be spreading the disease by means of their droppings-some of which got onto fruit,which young children were apt to eat without washing.
No evidence was offered,but there was a parallel situation,in which fruit bats were found to be spreading another filovirus by this means.
Another (remote ? ) possibility was deliberate use of biowarfare agents by someone in the Congolese government.
The "Democratic Peoples' Republic" was pretty close to the Russians at one time,and might have "inherited" some of their nasties.
Africa, as a continent, is almost totally ravaged. There are a billion people there, and probably 900 million are less than a month from starvation. The tribal wars have been devastating, the fall of European colonialism in Africa doomed them.
There is little doubt that Ebola and Marburg started there. The congo and central africa is still the place that has the highest genetic diversity on earth.
Only the Amazon basin might compare. And there's alot of nastys there too.