If you ever catch it.
...
The kids of South Park are exposed to Chicken Pox via the parents via a chicken pox party for the same reason. The kids find out about the "harm" intended by their parents to intentionally give their own children a virus. So, to exact revenge, they hire a local whore who has all sorts of nasty stuff living inside her to use the parents' tooth brushes and other repulsive contact transmission methods.
It's pretty funny. If you have Tivo and do a keyword on 'south park chicken pox', you'll only get that episode when it eventually comes on without having to wade through the other episodes.