The reason we have human mitigated global warming is, in the end, too many people. The reason we have so many wars is too many people. Most diseases require a minimum population density to spread. Some diseases are relatively benign, such as chicken pox or influenza (and really, they are not big killers), but others can be incredibly deadly like bubonic plague or Ebola.
Right now the saving grace about Ebola is that it really is, despite all the hysteria, relatively difficult to contract. But it's quite deadly, especially if you lack good treatment. I have to say, that I'm somewhat surprised that this current outbreak has less than a 50% mortality, pretty astonishing when you know just how terrible it is. Even the worst case scenario won't have it causing significant deaths in this country, but if parts of Africa? If it truly got out of hand an awful lot of people could die. Right now a total of about 5,000 people have died in three countries with a combined population of around 22 million people. So in reality, a very tiny percentage of people have died from this disease. The potential for many millions more to succumb is very real.
From what I've read about diseases and population, it seems as if the Black Death in the 14th century was the only event that actually reduced population significantly. There were places in Europe that more than 400 years later had not recovered, although by then the total number of people in Europe had far exceeded the number before the Plague. Humans are remarkably good at reproducing. For all that certain specific countries have actually reached zero population growth, they don't make a dent in the world total.
I can have ideas and hypotheses about what might happen, but I don't have a crystal ball, and I'm not about to suggest any sort of time line. But the more people there are, the more misery there will be.
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