In what is no doubt a planned release in correlation with J.K. Rowling and Harry Potter's birthdays, the final chapters of Goblet of Fire have been revealed on Pottermore.
Rowling addresses disability and illness within the Wizarding World and how it differentiates from Muggles.
I decided that, broadly speaking, wizards would have the power to correct or override 'mundane' nature, but not 'magical' nature. Therefore, a wizard could catch anything a Muggle might catch, but he could cure all of it; he would also comfortably survive a scorpion sting that might kill a Muggle, whereas he might die if bitten by a Venomous Tentacula. Similarly, bones broken in non-magical accidents such as falls or fist fights can be mended by magic, but the consequences of curses or backfiring magic could be serious, permanent or life-threatening. This is the reason Gilderoy Lockhart, victim of his own mangled Memory Charm, has permanent amnesia, why the poor Longbottoms remain permanently damaged by magical torture, and why Mad-Eye Moody had to resort to a wooden leg and a magical eye when the originals were irreparably damaged in a wizards' battle; Luna Lovegood's mother, Pandora, died when one of her own experimental spells went wrong, and Bill Weasley is irreversibly scarred after meeting with Fenrir Greyback.