I think a lot of germs like Ebola are manmade experiments that got away from clandestine government operations. Having them in Africa was perfect. Make up some story about some pervert having sex with monkeys, or africans eating bushmeat, or hiking in some exotic cave somewhere and there's the excuse. SARS will one day be outed for a biological weapon experiment gone bad.
Cy, that's sort of what I suspect.SARS,for example, is related to the common cold virus.