I’m keen on this one, think Arachnaphobia….
It is a zombie movie x the plague. Little bugs (as an analog for fleas) spread the virus. But it is represented as them latching onto to you and controlling you. Like parasites controlling insects, perhaps include that in the story as a science video…
The bugs are almost too small to see until too late. They crawl up your legs, they enter your mouth while you sleep. They are seemingly unstoppable.
A team of scientists, already working in a very remote place, get a chance to prepare. They work out how to detect the bugs, and how to kill them (fire). At the end they are on a mountain, blasting bugs, and we see an infinite number of bugs on their way. Insurmountable.