Discovery of The Vector
Nicolle's discovery came about first from his observation that, while epidemic typhus patients were able to infect other patients inside and outside the hospital, and their very clothes seemed to spread the disease, they were no longer infectious when they had had a hot bath and a change of clothes. Once he realized this, he reasoned that it was most likely that lice were the vector for epidemic typhus.
In June 1909 Nicolle tested his theory by infecting a chimpanzee with typhus, retrieving the lice from it, and placing it on a healthy chimpanzee. Within 10 days the second chimpanzee had typhus as well. After repeating his experiment he was sure of it: lice were the carriers.
Further research showed that the major transmission method was not louse bites but excrement: lice infected with typhus turn red and die after a couple of weeks, but in the meantime they excrete a large number of microbes. When a small quantity of this is rubbed on the skin or eye, an infection occurs.
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