Abstract

After the louse transmission of epidemic typhus had been established (1909), a small microorganism (thought to belong to a new genus, Rickettsia) was shown in enormous numbers in the guts of lice that had fed on human typhus victims. Attempts at cultivating this organism on inert media failed; tansfer from louse to louse without loss of virulence for the vertebrate host was successful. Some scientists were not convinced of the etiologic role of Rickettsiae, because the presence of this microbe in blood and organs of victims or of experimentally infected animals was difficult to demonstrate. This uncertainty was dispelled in 1928, when in guinea pigs infected with material from the closely related disease Tabardillo (murine typhus) abundant Rickettsiae were revealed in the tunica vaginalis. Live vaccines, derived from strains of murine typhus and deployed in French North Africa, were considered by outside observers as unsafe. Killed vaccines were derived from the masses of Rickettsiae present in louse guts, in chick embryo yolk sacs or in vertebrate lungs. These developments were not spurned by any 'upswing of virology' but by the threat of typhus in endemic areas and, after 1938, in a war-torn world. Their basis was firmly anchored in bacteriological thought styles and techniques