The Neutralization Technique in Tsutsugamushi Disease: (Scrub Typhus) and the Antigenic Differentiation of Rickettsial Strains

Abstract

Neutralization of R. orientalis by homologous antiserum was most effectively demonstrated when mice were inoculated by the intraperitoneal route with mixtures of undiluted antiserum and serial dilutions of infective material. Satisfactory results could not be obtained by employing a constant infective dose and serial dilutions of antiserum or by using the subcutaneous or intracerebral routes of inoculation. Furthermore, neutralization was independent of complement. Evidence was obtained to suggest that neutralization depends principally upon a union of antigen and antibody in vitro; however, passive immunity may best explain the zone phenomenon often observed. The satisfactory expression of the neutralizing capacity of an antiserum was rendered difficult by the above-mentioned zone phenomenon and by the otherwise frequently irregular pattern of mouse survival observed in neutralization tests. In spite of this difficulty, it was possible on the basis of a large series of crossneutralization tests to distinguish 4 clearly differentiated antigenic types and a possible fifth type among the 8 strains of R. orientalis included in the study. These types differed not only qualitatively but also in point of quantitative antigenic capacity.