Materials And Methods

Field samples were collected by night shooting and trapping from four pastoral localities where possums were of moderate to high population density. Following bleeding, sex and age-group were determined and the animal tagged for identification. Animals were divided into juvenile, transitional-stage adult and mature adult groupings. Differentiation was made on sexual maturity parameters: juveniles had testes lengths < 18 mm (males) or had undeveloped pouches (females); transitional-stage adults were sexually mature but weighed less than 2.4 kg and lacked the conformation of fully grown adults; mature adults weighed 2.4 kg or more and had fully mature head and body conformation.

Sera were tested by the microscopic agglutination test (M.A.T.) against reference antigens ballum, pomona, copenhageni, tarassovi, hardjo and balcanica. The reciprocal of the final dilution of serum that agglutinated 50% of the test antigen was taken as the titre of that serum.

Kidneys were aseptically removed within 3 hours of death and cultured. A 'Coleworth Stomacher¹' was used to homogenate whole kidneys and three serial ten fold dilutions were inoculated into EMJH² semisolid media.