Vector Insects

A vector insect is one used by another insect as a vector to infect a human host. The vector insect is trapped and eggs are laid on it. When the vector insect bites, stings or in any way does whatever it does to a human, an egg is laid on the human host. The human's body heat activates the egg which uses the vector insect's injury to get under the skin (literally). Once inside the egg grows to a full and rather disgusting larvae.

The potential use for this in a monster manual is huge, albeit a bit appalling and it does scream GM fiat all over. Imagine all those little critters you once found in a dungeon now laying eggs on mosquitoes that fly into town. Remember the dreaded rot grubs? Now you don't have to journey deep into the forest or a dungeon. They're delivered fresh to your home by your friendly mosquito.

Or maybe the villages honey bees are now infected with some terrible bug using them as vector insects. 

Why stop with insects. Curses and even zombification can be airborne on mosquitoes and other vector insects. Maybe even the G'ould evolved to be airborne that way. Chilling thought.

Source

http://www.iflscience.com/health-and-medicine/nsfl-botfly-removal-5-year-old%E2%80%99s-eye

http://forum.rpg.net/showthread.php?680134-Why-did-D-amp-D-amp-Pathfinder-art-become-so-stylized/page6