Serological studies and isolations of serotype hardjo and Leptospira biflexa strains from horses of Argentina.

Three pathogenic leptosipras and 12 saprophytic Leptospira biflexa strains were isolated from 72 apparently normal horse kidneys collected at an abattoir in Argentina. Cross-agglutination reaction patterns of the pathogens showed that they were antigenically homologous with members of the Hebdomadis group. When one of the strains was compared to Hebdomadis serotypes in reciprocal agglutination-absorption tests, it was found to be serologically homologous to serotype hardjo. This is the first known report of an isolation of this serotype from horses. Serological tests were also carried out on randomly collected abattoir sera from 245 horses to determine the prevalence of equine leptospirosis. Significant antibody titers (1:100 or greater) were found in 74.6% of the sera. Predominant reactions occurred with the antigens pomona, hebdomadis group, pyrogenes, tarassovi, and canicola. Agglutination tests performed with antigen prepared with one of the saprophytic biflexa isolates showed seropositive reactions in 99.1% of the equine sera, with agglutination titers ranging from 1:100 to 1:3,200. Absorption of selected horse sera with the saprophytic strain removed the agglutinins to Leptospira interrogans serotypes. This suggests the possibility that L. biflexa strains may act as an antigenic stimulus and account for some of the persistent multiple cross-reaction patterns of equine sera with pathogenic serotypes.