A serious epidemic has swept the land. Fox fever, caused by the vulpine virus, is highly contagious condition which causes non-vulpine furs to start to exhibit foxy characteristics and behaviours. At best, it can cause a sudden streak of mischievousness and a craving for poultry, and at worst, it causes the afflicted to actually become a fox!
The virus works by entering the bloodstream and injecting cunning compounds into host cells, which then become foxified. Unfortunately, because this virus is so sly, it has been able to outwit every vaccine tried on it. But, the furmune system does have one final trick up its sleave. Behold, the skunkocyte, which is able to spray antibodies which both deter and mark the virus out for miles!

This was inspired by some fun shenanigans on the forums! Special thanks to Simo-the-Skunk for giving me this idea! :D