Plague!

It's horrible having a fever feeling sick and getting spots and rashes isn't it But look inside this book and you'll witness the true horrors people faced in the past - rotting skin dissolving lungs and sinister pustules and swellings all over the body.
The Black Death wiped out whole towns and villages
Tuberculosis consumed young people like a blood-sucking vampire
Smallpox left its victims scarred for life - if they survived.
No one knew where these killer diseases came from or how to treat them. Frightening See how people tried to ward them off and made vital discoveries. The Egyptians chewed garlic to keep malaria at bay an English physician found a source of cholera and a Cuban doctor showed that mosquitoes spread yellow fever - all pieces in the giant jigsaw puzzle of modern medicine.