- "We're going to put out the story that I'm seriously ill with spattergroit, which is why I can’t go back to school. If anyone comes calling to investigate, Mum or Dad can show them the ghoul in my bed, covered in pustules. Spattergroit’s really contagious, so they’re not going to want to go near him."
- —Ron Weasley[src]
Spattergroit is a highly contagious wizarding disease. It may be a type of fungus, as Ron Weasley mentions that being unable to talk is a common effect of spattergroit “once the fungus has spread to your uvula”. A person sick with spattergroit will also get purple pustules over his or her skin and be bedridden, suggesting that fatigue is another symptom. It is potentially fatal.
Harry first learned of the disease in 1995 when he visited Mr. Weasley in St Mungo's Hospital for Magical Maladies and Injuries. While heading for the hospital's tea room, a Healer in a magical portrait diagnosed Ron with the disease, given the "unsightly blemishes" on his skin that would leave him uglier than he already is. The portrait suggested that Ron "take the liver of a toad, bind it tight about his throat and stand naked by the full moon in a barrel of eels' eyes". Ron took this diagnosis as a great offence, and countered that they were only freckles. It is unknown if this treatment actually works.
Ironically, the family ghoul was later transfigured and given purple pustules by Arthur, Fred and George Weasley to resemble Ron with the affliction. This ruse was spread in order to explain his absence from school. Hence, when he did not appear at Hogwarts for his seventh year, his family could claim that he was too ill to attend, due to the fact that attendance at school was mandatory for that year.