ABSTRACT
There are two distinct types of true typhus virus. The diseases they cause in man are identical and both are transmitted from one individual to another by human body and head lice. Typhus fever was born when the first infected rat flea fed upon a man. This accident probably took place — most likely somewhere in the East — centuries before the disease reached the crowded centres and the armies of mediaeval Europe. The murine virus was the original typhus. In the course of time the disease was carried, perhaps repeatedly, to Western countries — chiefly by armies, at first causing limited outbreaks that perhaps ended with the virus still remaining largely or entirely murine. In approaching the problem, investigators began to pass both types of virus through a variety of insects, through guinea pigs, rats, and mice, and to collect for study all the strains they could get hold of from rats and from human patients.
