"It is typhus fever"

US World War II advert
Public DomainUS World War II advert - Credit: US National Archives and Records Administration
Typhus is any of several similar diseases caused by Rickettsia bacteria. The name comes from the Greek typhos, meaning smoky or hazy, describing the state of mind of those affected with typhus.  Symptoms include chills, a bad cough, delirium, high fever, joint and muscle pain, headaches, low blood pressure, rashes and sensitivity to light.

A major epidemic occurred in Ireland between 1816 and 1819, in which an estimated 100,000 people died. Another epidemic hit Ireland during the Great Famine, between 1846 and 1849. The epidemic spread to England, where it was sometimes called "Irish fever".  It killed people of all social classes, as lice were endemic and inescapable, but it hit particularly hard in the lower classes of society.