Nicolle's discovery of louse-borne typhus

Typhus came to Tunis in waves each cool season. Charles Nicolle, a bacteriologist from Rouen, became director of the Pasteur Institute of Tunis in 1903. Most doctors in the Tunisian service, especially in the countryside, caught typhus, and about a third of them died of it. Early on, Nicolle arranged to join a colleague on a visit to a prison 80 kilometres south of Tunis. The evening before, he coughed up blood and stayed behind. His colleague Motheau and a servant went, caught typhus and died.

At the native hospital in Tunis, Nicolle often had to step over typhus patients who had collapsed at the door. Before admission, he noticed, patients infected their families, visiting doctors, the clerks who admitted them and the staff who took their clothes and washed their linen. Once in the general wards they infected no one. Between the door and the ward, each patient was stripped, shaved and washed. The agent, Nicolle reasoned, was something on the skin and clothing that soap and water removed: the body louse.

Proof needed an animal that could catch the disease. Small monkeys had resisted infection, so Nicolle asked his teacher Émile Roux in Paris for a chimpanzee. In June 1909 he gave it typhus with a patient's blood and passed the infection by blood to a macaque. On 6 September 1909 Roux presented to the Academy of Sciences a note by Nicolle, Charles Comte and Ernest Conseil. They had placed 29 lice, taken from people that morning, on the infected macaque after its rash appeared, then moved them day after day to two healthy macaques. Both developed fever; one died on the 44th day. Measures against typhus, the note concluded, must aim at destroying the parasites on patients' bodies, linen, clothing and bedding.

In 1910 Howard Ricketts and Russell Wilder confirmed louse transmission in Mexico, and Nicolle found that louse faeces became infective at the same time as the bite. Later work showed that the main route was louse excrement rubbed into the skin or eyes. Nicolle's discovery that guinea pigs could be infected let the agent be kept in the laboratory all year, and in guinea pigs with no symptoms he recognised inapparent infection. The Nobel presentation speech credited Nicolle and his colleagues with ridding Tunis of typhus within two years. Ricketts and Stanislaus von Prowazek both died of typhus caught in their research, and in 1916 Henrique da Rocha-Lima named the organism Rickettsia prowazeki after them.