An unknown magical bug
Scrofungulus is a wizarding illness. It is a contagious disease and is provoked by an unknown magical bug. The "Magical Bugs" section of St Mungo's Hospital for Magical Maladies and Injuries treats this disease.
Scrofungulus could possibly be a mix between "scrofula" (the former name of tuberculous cervical lymphadenitis, a type of tuberculous that normally infects the neck), and "fungus". If so, then it is possible this disease is caused by a fungus that infects the neck region.
- Harry Potter and the Order of the Phoenix (Mentioned only)