Seroepidemiology of Leptospira interrogans serovar hardjo in Colorado antelope and cattle

A seroepidemiologic study was conducted to determine the prevalence of Leptospira interrogans serovar hardjo infection in Colorado cattle and antelope. Sera were tested by the microscopic agglutination test, using a standard battery of 12 antigens as well as 4 additional serovars of the Hebdomadis serogroup: hardjo, szwajizak, sejroe, and balcanica. Sera from 1,856 cattle and 544 antelope were tested. In both populations, the predominant serovar detected was hardjo; hardjo titers greater than or equal to 1:400 were found in 3.2% of the cattle and 3.6% of antelope. A positive correlation was found to exist between serologic evidence of infection in cattle and the presence of antelope. In counties with presumably infected antelope, 5.6% of cattle sera reacted to hardjo; in counties with uninfected antelope, 2.6% of cattle tested were seropositive for hardjo; where no antelope existed, titers of greater than or equal to 1:400 were not detected.