Looking for a short story.
Background was there were a ship of alien viruses(vampires) intended for a night planet that had crashed on Earth long ago and were accidentally activated by radio transmissions of the developing human race.
Plot is a vampire hunter (also alien but humanoid) is sent to exterminate the vampires. The story takes place in a building that is surrounded and force-fielded off where the hunter exterminated the vampires.
This is "Infestation" by Garth Nix, first published in The Starry Rift, edited by Jonathan Strahan, 2008. I read it in To Hold the Bridge.
Starts with a group of vampire hunters gathering to clean out a newly found infestation of vampires. There is a secure perimeter guarded by soldiers, and only licensed vampire hunters are allowed to enter. Most of the hunters are amateurs, but the narrator is a professional.
Over the course of the story we learn some of the history of the vampires and the narrator. In short, in an alien war, a team of vampires was landed on the wrong planet (Earth). The narrator is an alien whose mission (punishment) is to eradicate the infestation from Earth.
THere is a copy online at https://talesofmytery.blogspot.com/2013/02/garth-nix-infestation.html
