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I'm interested in coming up with a plausible agent of destruction, virus or fungus or engineered weapon or what have you, that could conceivably wipe out a majority of the human race. What physical attributes should it have in order to do maximum damage without being stopped by the authorities? The survivors would be those immune to it.

Based on some research I've done, the agent would need to have the following:

  • Be airborne, to make it easier to spread
  • Extremely contagious - very easily passed on from person to person
  • Longer incubation period - if the agent kills too quickly, it'll be contained easier
  • Symptoms which are not too extreme and could be confused with the signs of a lesser, more benign illness
  • Resistance to antiobiotics - maybe biofilms?

I'm basically looking to flesh out the above, with some plausibly concrete numbers. i.e. how long would the incubation period be ideally, what kind of defense it would have against antibiotics etc.

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  • $\begingroup$ What level of technology, disease spreads differently with modern air travel available. $\endgroup$ – John Oct 28 '19 at 17:51
  • $\begingroup$ en.wikipedia.org/wiki/Plague_Inc. $\endgroup$ – Halfthawed Oct 28 '19 at 18:25
  • $\begingroup$ @John About 20 years from current-day, so not too much of a difference - just larger, denser world population $\endgroup$ – Space_Cadet Oct 29 '19 at 13:21
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The best examples of far reaching global pandemics are the Black Plague and the 1918 influenza epidemic. Apart from not having the kind of lethality rate you're looking for, both examples were able to spread widely due both to a lack of any effective means of controlling travel, and a widespread lack of effective medical care.

If you're envisioning a modern pandemic then, your disease needs to spread faster than it can be quarantined, and be widespread before alarmed governments can shut down international travel and quarantine impacted communities.

As far as your first two criteria are concerned, you can just look at influenza. It's airborne and incredibly contagious. For the third and fourth criteria, you have a couple options.

Option 1 is that the disease has a moderate incubation period, say 4-8 days, and a gradual decline during which the person thinks they just have a normal flu that hangs around for a week or two, during which they're still actively moving around and infecting people, before they start getting REALLY sick and eventually die.

Option 2 is a unusually long incubation period of more like 10-20 days, after which the infected individual becomes increasingly symptomatic over days and dies very quickly.

Option 1 has the greatest potential for distribution in that by the time anybody realizes there's an epidemic occuring, the infected percentage of the population is VERY high. However, it also allows the most time for response and treatment once the global medical community becomes aware of what's going on.

Option 2 allows less overall time for distribution, but when people started getting sick, there would be millions and millions of dead all at once, and with a spread pattern like this, medical professionals would be most at risk of infection and death before any countermeasures could be devised, which also addresses your fifth item. If it's not susceptible to standard antibiotics/antivirals/antifungals, then under these conditions by the time someone figured out (or developed) something that DOES work, it would be too late.

I'll also point out that the actual disease doesn't have to be what kills EVERYBODY. Throughout the developed world at least, the way most people live relies on a complex and rather fragile economic system that ensures that food and clean water and electricity and so forth get to everybody. If you had enough people die quickly enough from the virus (say 30-40% of the population), that would conceivably disrupt things so badly as to cause catastrophic collapse of industrialized society almost overnight, which means that the people who didn't die immediately from your superflu or whatever would still die anyway from violence, starvation, and the more normal diseases associated with having a few million dead bodies lying around with nobody to handle it.

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Model Your Virus After HIV-2

There are two varieties of HIV. HIV-1 is the one epidemic to sub-Saharan Africa. It is substantially faster-acting, in order to be more infectious. HIV-2 is the one more common to Europe and North America, which is less infectious, but can take as long as ten years before turning (barring antiviral therapy) into AIDS.

AIDS is already a pretty nasty payload, but if you borrow from something like hemorrhagic fever for its eventual amplification, you gain the benefit of a society-disrupting, terrifying final stage. Ebola manifests as flu-like unpleasantness before it goes terminal, which would likely keep people from noticing what is happening until the death toll really starts to mount.

So your characteristics need only be twofold: long, long infectious incubation period, on the order of years, and a truly horrific amplification step. It needn't be airborne - look at cholera as an example of an extremely successful non-airborne virus.

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  • $\begingroup$ The problem with it not being airborn is things like cholera have largely been eliminate via simple sanitation. $\endgroup$ – John Oct 28 '19 at 17:52
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    $\begingroup$ @John - there were four million cases of cholera last year. I don't think that's "largely eliminated". HIV is sexually transmitted, and there are 40 million active cases of that. You don't need airborne communication with a long enough incubation period. $\endgroup$ – jdunlop Oct 28 '19 at 18:03
  • $\begingroup$ @John see: Norovirus. Not airborne, requires a lot more than just 'simple' sanitation to defeat. $\endgroup$ – Morris The Cat Oct 28 '19 at 18:17
  • $\begingroup$ @jdunlop all in places without modern sanitation. $\endgroup$ – John Oct 28 '19 at 18:36
  • $\begingroup$ @MorrisTheCat norovirus can go airborne. Recent research has shown norovirus induced vomit can actually aerolize the virus, it is not as good at spreading through the air as other viruses that can spread via dry particles, but it is still airborne. $\endgroup$ – John Oct 28 '19 at 18:53
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Have you considered a modified prion (modified to be more contagious)? The interesting thing about prions is they are not alive and are therefore impossible to 'kill.' If you've ever played the game plague then you know the key to destroying the world is to keep your pathogen dormant long enough that the authorities don't notice it until everyone is already infected. Your ten percent survivors would then just harbor natural immunity.

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Something truly terrifying would be a genetically designed Cordyceps fungus that targets humans.

In insects Cordyceps specifically act on one species, some selectively destroy parts of the brain and force the Host to climb to a high point and latch on. Then they grow inside the body and erupt in fungal towers that spread spores.

https://www.livescience.com/20099-ant-zombie-mind-controlling-fungus.html

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