Is non-manmade pandemic a realistic threat to modern first world?

Inspired by this question, and my own answer to it: Avoiding galactic pandemics. World ending pandemics are a common disaster/after-the-end story trope, I'm trying to determine if plausible, and how one could occur.

What is the threat of a pandemic occurring in a modern first world nation, and if one is plausible then what conditions are required to make it occur? Keep in mind I'm talking about trying to stay to the realm of realistic science, in particular only diseases that plausibly could evolve in the first place.

I define a pandemic for this question as:

1. Naturally evolved, or at least not intentionally man-made. I'm willing to accept diseases that evolved due to accident's or mistakes made by man, such as breeding antibiotic resistant bacteria via overuse of antibiotics, but no weapons-grade engineered diseases.

2. Disease must spread for at least half a year without being contained

3. Has a mortality of at least 10% (ie kills 10% of total population)

4. Is a threat to modern-day first-world countries that aren't willfully ignoring the threat (like some African countries are doing with AIDS).

How plausible and what is the threat of such a pandemic?

Edit: Just to clarify, my interest is not in what sort of virus could be a threat, but how realistic such a virus existing would be! I am particularly looking for information about the likelihood of any suggested virus actually occurring.

Most relevant, the 'ideal' virus is one with a long incubation period and one that is not obviously lethal until long after symptoms are seen. However, I believe the more lethal the virus the shorter the incubation and quicker the time between symptoms and death would be. So if a virus must have a long incubation to be dangerous, I would appreciate at least addressing the likelihood of a long-incubation virus evolving.

posted over 9 years ago

dsollen‭

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