A sero-epidemiological study of Leptospira interrogans serovar Balcanica in four brush-tailed possum populations in Victoria, Australia.

The microscopic agglutination (MA) test was utilised to study the prevalence of antibodies to Leptospira interrogans serovar hardjo in 4 populations of brush-tailed possums (Trichosurus vulpecula). The overall antibody prevalence varied from 14% to 66%; however, the age distribution of MA test titres was remarkably similar in all 4 populations. Antibody prevalence was similar in both males and females and demonstrable antibodies were limited to sexually mature animals. The greater prevalence of high titres (greater than or equal to 1:128) in the 18- to 24-month age group suggested that primary infections were acquired at this age. The findings suggested that infection was maintained in possum populations by direct transmission, probably associated with breeding. Focal interstitial nephritis was observed in kidneys of possums greater than 18 months of age and was associated with MA titres to hardjo (P less than 0.001). Serovar balcanica was isolated from possum kidneys from 2 of these populations, suggesting that balcanica infections were responsible for most of the hardjo titres. However, agglutinin-absorption tests indicated that some possums may be infected with a leptospire more closely related to hardjo than to balcanica.