OK, well, you need to have someone find the nest, and get rid of it; and you will have to make sure there are no other places other than the vent where they can get in, and close those up.
I am here as well; I have merely been keeping a low profile. Wishing you well with your diagnosis @Charlet. Knowing for certain what it is that ails you is the first step toward effective management of it.
Did you know....the horns on the viking's helmets are a myth? The popular image of the "horned Viking" can be traced back to the 1870s. Costume designer Carl Emil Doepler created horned helmets for Richard Wagner’s opera cycle Der Ring des Nibelungen to enhance the characters' theatrical presence. (I BELIEVE in the Where in Time game, they tell us this too....)