Fruit bats are a reservoir for many nasty little diseases--Ebola being one of them. Bush creatures (monkeys, animals, whatever) come in contact with or eat infected bats, humans eat bushmeat and get infected. Rinse and repeat, that's caused every outbreak since the discovery of the Ebolavirus family (yes, there's different ones) in the summer of 1976. It probably was around before then, but that's the first time it was officially discovered and named.
In this outbreak, patient zero is assessed to be a 2 year old child in Guinea who died at the end of December 2013. (
http://who.int/csr/disease/ebola/ebo...t-big.png?ua=1)