Swamps are particularly dangerous areas. Here is how they work; picture swamp rooms as rooms with real and fake directions. Also, they are rooms where you lose your orientation, just like some caves (this might not be initially apparent). So, each room has real and fake exits and the directions are shuffled.
Whenever you type an exit, if you were lost and didn't 'guess' a real direction, you *will* fall into a swamphole. There is no skill check involved. Now, if you were not lost (because you have *high* swamp lore and location sense or you used a compass or did a 'guess direction' with good astronomy) and type a fake direction, you will *also* fall into a swamp hole.
Basically, whenever you end up going into a fake direction, that's a swamp hole.
My advice when going into swamps is to:
1) Bring a compass and use it in every room.
2) If you don't have a compass. Guess direction in every room.
3) Make a map. This will be a long and tedious process, but you will then forever be ok inside the swamp
(Or you could ask people for a map, i.e., the Scribes)
4) Bring a knife and cut leeches off as soon as they appear.
5) Don't wear any boots. Specially if you have stuff in them!
As for what to do with Marika right now, I don't know what this mosquito bite is or does. I guess it's tetanus. I'd recommend grabbing a piece of grid paper and starting to map. Don't lose hope, because as long as you're typing *real* exits, you will be OK. The exit of the swamp will mostly always be north-ish, though it depends if it's the west or the east side of the swamp. Also, look out for the river, I believe you can enter the river from the swamp in some spots, and that's a free way out if you're good at swimming.
Hope this helped!