Vaccination Against Spotted Fever with Agar-Tissue Cultures

Abstract

The making of vaccines against the Rickettsial diseases with the contents of infected insects offers many technical difficulties to say nothing of the danger to those involved. There is no doubt that vaccines prepared in this manner by Weigl for European typhus, and by Parker for spotted fever, give considerable immunity. 1 , 2 To eliminate the danger and expense of manufacture, culture vaccines of rickettsiae are the ideal, but until recently it has not been possible to obtain cultures that were sufficiently rich to permit vaccination on a large scale. By means of the agar slant method previously reported, we have been able to make vaccine which protects guinea pigs 3 and monkeys 4 against large doses of European typhus. It was hoped that spotted fever vaccine made in the same manner would be equally efficient.

Culture strains of spotted fever (Eastern type) are easily initiated with spleens of infected guinea pigs. 5 After the first generation, mouse embryo tissue is used. For the preparation of vaccine, the infected material from slants is ground in a mortar, and 3 cc of formol-saline is added for each slant. In vaccinating guinea pigs, a total of 4 cc of vaccine is administered subcutaneously in doses of one, one, and 2 cc at 5-day intervals. Animals so treated are found to be solidly immune when tested a month later with blood virus (Chart 1). Serum from 2 vaccinated pigs taken 3 weeks after vaccination agglutinated spotted fever rickettsiae (chick tissue slants) in dilution of 1/20+++, 1/40++, 1/80+. These 2 sera also protected normal guinea pigs when 1 cc was mixed with passage blood and injected after standing 40-60 minutes at room temperature.