Originally Posted by The Heron

I think it's more probable now than ever that we could get wiped out by a disease. Consider modern travel allows for very quick spread worldwide.
Humans are less diversified than ever before.
Modern medicine has weakened our natural immunities, provides false security and worst actually breeds super bugs.
Humans are overpopulated (disease is major population control).

I'm surprised we haven't all died from some crazy african disease yet but it will happen soon enough and there's not much you can do to prevent it.