‘Gingervitis’ was made popular by South Park‘s ‘Ginger Kids’ episode. They say that having red hair, pale skin and freckles is something that is a contagious disease, and that you must avoid being bitten by a redhead, otherwise you’ll turn ginger too.
They also throw in that not having a soul is another symptom of ‘gingervitis’.
Oh, and in case you hadn’t noticed, ‘gingervitis’ is a play on the gum disease ‘gingivitis. Oh, how clever.