What type of viral/bacterial/fungal infection causes the fastest symptom response?
Too many sci-fi movies make it seem like you've got minutes before catastrophic symptoms appear after being exposed, but what's the most realistic timeframe for an infection to cause a severe response?
Honestly, pretty fast. You could look at cases of bowel rupture, where a large amount of bacteria quickly gains access to the bloodstream, causing sepsis and rapid death without immediate intervention. Can go from infection to death in half a day.
If we're just asking for a severe response instead of death, it just depends on how severe it needs to be. The bacteria is throughout your body within minutes, flowing at the speed your blood circulates, and almost immediately triggering a massive immune response. This immune response leads to shock, which is what kills you.
So, something like botulism (according to Health Canada) can take 12 - 72 after ingestion for symptoms to appear. But even that seems pretty damn slow. Anthrax is even slower.
Are there any which cause symptoms in minutes?
Again, my context is that movies make it seem like if you're scratched by something infectious, you've got minutes before you're a zombie. LOL
Theoretical zombifying pathogens have a few additional hurdles to pass. One, they can't destroy your tissue, because it's still necessary to operate the body. Two, they need access to your brain, which your body has a natural barrier protecting. Pathogens have a hard time getting in unless they start very nearby. Third, it'd have to alter your brain in such a way that a lot of behavior was left intact without destroying basic motor function and some simple logic.
This just isn't easy to do. Probably would require some kind of super spiffy sci fi nanotechnology to actually pull off. Like, if Tony injected his fanciest suit's nanites into your body and controlled them remotely, he might be able to ask Jarvis (or whoever it was, I forget) to zombify you.