Detection of leptospiral antibodies in animal sera by means of fractionated antigenic extracts.

Sodium dodecyl sulphate extracts of the reference strains Mus 127, Castellón 3 and Arborea of the Ballum agglutinogenic serogroup of Leptospira interrogans (the species of pathogenic leptospira), of strain Patoc 1 of the saprophytic species of L. biflexa, and of strain 3055 of illini serotype, the sole representative of L. illini, were each fractionated by ultracentrifugation in a sucrose density gradient into 10 fractions. The fractions were tested by complement fixation and immunodiffusion against the sera of animals during the process of immunisation and during the course of naturally occurring infections. The fractions could be divided into three main pools of serological activity: pool I (fractions 1, 2 and 3), pool II (fractions 4, 5 and 6), pool III (fractions 7, 8 and 9). Pool I was species/genus specific; fraction 1 tended to be species specific while fraction 2 reacted with antisera to all strains whether pathogenic or saprophytic. Pool II was serogroup specific and reacted only with antisera to members of the same serogroup. Pool III was serotype (serovar) specific and revealed the identity of the infecting strain at an early stage of infection.