During a widespread famine that immediately followed the end of the Napoleonic Wars, a million and a half people fell ill from typhus in Ireland, of whom some 65,000 died.
As impoverished and desperate Irish migrants fled famine and disease, they became the vehicle of widespread prejudice in the 19th century as Typhus became known as "Irish Fever".
The Irish were caricatured in racist cartoons as savages, barely human, the northern equivalent of the 'negro' in the South, on a lower stage of civilization than the rest of society.
In the mid-nineteenth century a third wave of the bubonic plague began in China. Merchants and Traders quickly spread the disease across the globe with outbreaks occurring Glasgow, Paris and San Francisco.
Not surprisingly, the threat of bubonic plague led to a major outbreak of nativist anti-Chinese sentiment in the USA. In 1899, the Chinese quarter in Honolulu was isolated, disinfected and eventually burned to the ground when the destruction of infected buildings got out of hand;
Unlike earlier outbreaks of the bubonic plague, by now the causes of the disease were known. A bacteria, Yersinia Pestis was discovered in 1894 and a few years later the hypothesis of its spread by rats and fleas was accepted. In 1907, when the second outbreak of plague hit San Francisco, the authorities offered a reward for each dead rat brought in.
From the beginning Nazis used the language of disease and bacteria to dehumanise the Jews. German authorities justified forcing Jews into ghettos as a 'sanitary measure' then created the unhygienic, insanitary and overcrowded conditions in the ghettos that provided the ideal breeding-grounds for the diseases like typhus. By the autumn of 1941, the hospitals in the Warsaw ghetto were treating around 900 typhus cases a day.
Typhus became the justification, not just for medical intervention but for genocide.