SERO-EPIDEMIOLOGICAL STUDY OF LEPTOSPIRA-INTERROGANS SEROVAR BALCANICA IN 4 BRUSH-TAILED POSSUM POPULATIONS IN VICTORIA, AUSTRALIA

The microscopic agglutination (MA) test was used to study the prevalence of antibodies [Ab] to L. interrogans serovar hardjo in 4 populations of brush-tailed possums (Trichosurus vulpecula). The overall Ab prevalence varied from 14-66%; the age distribution of MA test titers was remarkably similar in all 4 populations. Ab prevalence was similar in males and females and demonstrable Ab were limited to sexually mature animals. The greater prevalence of high titers (.gtoreq. 1:128) in the 18-24 mo. age group suggested that primary infections were acquired at this age. Infection was apparently maintained in possum populations by direct transmission, probably associated with breeding. Focal interstitial nephritis was observed in kidneys of possums greater than 18 mo. old and was associated with MA titers to L. interrogans serovar hardjo (P < 0.001). L. interrogans serovar balcanica was isolated from possum kidneys from 2 of these populations, suggesting that L. interrogans serovar balcanica infections were responsible for most of the L. interrogans hardjo titers. Agglutinin-absorption tests indicated that some possums may be infected with a leptospire more closely related to L. interrogans serovar hardjo than to L. interrogans serovar balcanica.