Ague (A-gyoo) is a severe fever that's marked by recurring chills, shivering, and sweating. Sometimes, ague refers just to the chills and shivering, topped off by joint and bone pain. Up until the nineteenth century, however, ague was the English word for malaria — a mosquito-borne disease that causes fever and chills. Malaria is usually associated with the tropics, so it sounds weird that the disease was a major cause of sickness and death in England from 1564 to the 1730s. Chalk it up to a bad combination of climate change, brackish water in rivers and marshes, and, of course, mosquitoes.
Ague was prevalent enough that Shakespeare mentioned it in nine of his plays. You'll also see ague surface in Robinson Crusoe, Treasure Island, and Gulliver's Travels. In Great Expectations, Pip takes some food to an escaped convict. As the convict stops eating to take a drink, Pip notes the illness:
[The convict] shivered all the while, so violently, that it was quite as much as he could do to keep the neck of the bottle between his teeth, without biting it off.
"I think you have got the ague," said I. . . ."It's bad about here," I told him. "You've been lying out on the [marshes], and they're dreadful aguish. Rheumatic too."