Ague

Ague is a term that refers to an illness (such as malaria) characterized by alternating fits of fever, chills, and sweating.

Treatment
Eating whole ashwinder eggs was a known magical cure for ague. There was also a potion that was used for curing ague. However, if it was brewed incorrectly, it could be fatal. Quintia McQuoid died in the early 15th century after consuming an improperly-brewed batch of this potion.

In the 12th century, Muggles in the village of Stinchcombe, Gloucestershire, regularly went to their neighbor Linfred seeking remedies for their ailments that afflicted them, not knowing that he was a wizard. He readily brewed potions for them, including cures for pox and ague.