Epidemic typhus

Epidemic typhus is caused by the bacillus Rickettsia prowazekii, carried by the human body louse Pediculus humanus. Feeding on a human who carries the bacillus infects the louse. R. prowazekii grows in the louse's gut and is excreted in the feces. The disease is transmitted to an uninfected human who scratches the bite and rubs the feces into the wound. Incubation period is one to two weeks. R. prowazekii can remain viable and virulent in the dried feces for many days. The disease will kill the louse and it will remain viable for many weeks in the dead louse.

Before World War II, epidemic typhus was a devastating disease for humans. Epidemics occurred throughout Europe from the 17th to the 19th centuries. It was common in prisons, where it was known as Gaol Fever. Before then there is little historical literature available. Widespread epidemics occurred during the Napoleonic Wars and the Irish potato famine of 1846 to 1849. During World War I the disease caused three million deaths in Russia and more in Poland and Romania. Even larger epidemics in the post-war chaos of Europe were only averted by the widespread use of the newly discovered DDT to kill the lice on millions of refugees and displaced persons. A vaccine was also developed in World War II, and today epidemics only occur in Eastern Europe, the Middle East and parts of Africa where living conditions and hygiene are poor.L_ _ _ _ _

Further reading: Rats, Lice and History (1934), by Hans Zinsser, a rather idiosyncratic history of the disease and its epidemiology. ISBN 1884822479