How it began
Charles Nicolle, a French physician, directed the Institut Pasteur in Tunis from 1903 until his death in 1936. He studied epidemic typhus there for seven years. At the Sadiki Hospital he noticed that typhus patients infected others, including those who handled their clothing, up to the moment they reached the waiting room, but stopped being infectious once they were bathed and dressed in hospital uniforms. He reasoned that lice in their clothes carried the disease.
Before it existed
Typhus had long been a highly communicable and often fatal disease of armies, prisons, famine and poverty, and how it passed between people was unknown. In Tunis it struck in the cooler months and spread through prisons, asylums and tent villages. Most doctors in the Tunisian health system had caught it, and about a third of them died. In 1903 two of Nicolle's colleagues died after a prison visit he had canceled at the last moment.
How it works
Nicolle injected a chimpanzee with blood from a typhus patient, and it fell ill within a day. He passed the infection to a macaque, fed 29 lice on the sick animal, then moved the lice to healthy macaques, which also became ill. He reproduced typhus in the chimpanzee in June 1909, showed lice were the carriers in August and reported to the French Academy of Sciences in September. Later research showed the main route is louse excrement rubbed into the skin or eyes.
What changed first
The experiments were confirmed quickly. In the following year Howard Ricketts and Russell Wilder, working in Mexico, confirmed louse transmission. In 1916 Henrique da Rocha-Lima identified the causative organism and named it Rickettsia prowazeki. Nicolle received the 1928 Nobel Prize in Physiology or Medicine for the discovery. His typhus work also led him to describe inapparent infection, in which hosts carry and pass on a disease without symptoms.
What lasted
Knowing the vector made control possible. After the insecticide DDT was found in the late 1930s to kill lice, several potentially severe typhus epidemics during World War II, notably in Naples in 1943 and 1944, were averted by dusting people at risk. A review in Emerging Infectious Diseases calls the discovery the beginning of the end of epidemic typhus, which is now uncommon.
