Like Bizzylizzy, lots of ticks and high prevalence of boreliose (sp?)also known as Lymes Disease here too. We're taught that the bullseye pattern and / or radiating lines of discoloration of skin are the bad signs.
All of our cats and dogs are affected at the moment. I've been known get one or two as well:-( So far no bad infections though.
Its really only worthwhile disinfecting where a tick has been removed. If the've already dropped off any infection will have already occurred. I guess the swelling we see is something to do with the anaesthetising spit the ticks inject to hide their presence.
Re Op question about what works as a deterrent, we use Fronline plus on the cats, and Barnaby the Cocker has a Bayer Seresto collar.