Active Immunization Against Tunisian Typhus Fever with Mexican Typhus Vaccine. 20

Abstract

Several attempts have been made to vaccinate human beings against typhus fever, both with living virus 1 and with killed rickettsia. Immunization with living virus is always dangerous, since it is extremely difficult to make accurate titrations of the virulent material, so any method yielding a rich suspension of killed rickettsia, safe to handle and at the same time producing an effective immunity would be a great help in typhus fever epidemics.

Weigl 2 obtained encouraging active immunizations by means of an emulsion of the triturated intestinal canals of infected lice, suspended in 0.5% phenolized salt solution. His vaccine corresponds to 100 lice per cc. and is administered in 3 weekly doses. In our experience this vaccine produces in man a rather severe reaction similar to that of typhoid vaccine. Although there is no doubt as to the effectiveness of the Weigl suspension, its manufacture on a large scale is not practical.

Following the discovery of Mooser, 3 who found, in the tunica vaginalis of guinea pigs infected with Mexican typhus, a small intracellular organism that by its characteristics has been identified with the rickettsia of the louse, Zinsser and Castaneda have attempted 4 to produce large amounts of these organisms which, killed in a convenient manner, would give suitable material for active typhus immunization. They succeeded in this by infecting rats previously treated with benzol or exposed to X-ray radiation. These rats present a massive infection of the peritoneal cavity, smears from which show an enormous number of intra- and extracellular rickettsia, giving the appearance of a culture. The peritoneal washings made with formalinized salt solution give a fairly strong vaccine.

In the following experiments we used a vaccine prepared by means of the benzol method, though actually we now prepare the vaccine by the recent X-ray technique published by Zinsser and Castaneda 5 which results in a suspension of rickettsia bodies as free as possible from rat serum and cells.