Considering what Mad Cow disease did to the cows, any human form could certainly be just as terrible.
Orgeeeeeee! There is a human form; nvCJD. However it's so rare you have more chance of being struck by lightning twice as contracting it. There's no denying the people who get it die in as distressing a way as anyone with dementia but a pandemic? Not a chance.
I'd guess you would need a lot less than 700 000 to build a stable civilization. A few thousands should suffice.
Probably even a few hundred. I'm sure there's probably some information somewhere about how few people you'd need to survive for humanity to flourish. Obviously the smaller the pool the greater the chance of genetic anomolies being passed along. Even if 700,000 survived I guess the difficulty would be that they won't all be in one place, in fact it's likely you'd never be able to draw them all together, either because of the problems in trying to contact everyone, or the logistics of getting together. How would survivors in Brazil link up with those in the UK for example. And actually you may not want them too, scattered settlements might be better than one big city of humans. It's too easy for one settlement to be destroyed I guess. But yeah it'd have to be one hell of a virulent inefection to kill every single human. And forget Madagascar , Greenland's the place to be. Those gits have thwarted my plans on Plague inc (great game) more times that any other country!
Actually it seems society might recover if there were just 70 people left! It might just take 20,000 years for them to reach our levels of civillisation again.
I wonder what the minimum population size needs to be in order for humanity to repopulate itself. Meaning, sufficient genetic diversity. Could it be as little as a thousand?
Ever read Tom Clancy? Executive Orders is about an air born strain of Ebola released on an airliner, infecting the passengers who pass it along. Don't know if it's possible, but the whole idea is pretty scary.
More likely if a truly horrific outbreak occurred in a city and measures could be taken before it spread to the countryside, there would be a military nuclear 'accident' and a very bright white flash.... Read Michael Criton's book The Andromeda Strain. Even back then nuking a town was a viable military contagion option.
^ And also Outbreak, although in that case they didn't use nukes, just a very powerful bomb. (In the novelization, anyway. The film has the town spared.)
According to the link I posted, Polynesia was colonised by just 70 people. I guess it may come down to what kind of genetic ticking time bombs were evident in the group's DNA though.